Relationships Between Secondhand Smoke Incursion and Wheeze, Rhinitis, and Eczema Symptoms in Children Living in Homes Without Smokers in Multi-Unit Housing

Relationships Between Secondhand Smoke Incursion and Wheeze, Rhinitis, and Eczema Symptoms in... Abstract Introduction Secondhand smoke (SHS) incursion can occur in units of multi-unit housing (MUH). The purpose of this study was to determine the relationship between SHS incursion and allergic symptoms in children living in MUH without smokers. Methods We conducted a cross-sectional study from May to September 2015 in Seoul, Korea. Children were recruited from elementary schools, kindergartens, and daycare centers. In total, 16676 children between 1 and 13 years of age living in MUH without smokers were included in the analysis. Allergic symptoms during the previous 12 months (current wheeze, rhinitis, and eczema) and home environmental factors, including the frequency of SHS incursion during the previous 12 months, were examined using a questionnaire filled out by the parents or guardians of the children. Results The prevalence of current allergic symptoms in children was 4.9% for wheeze, 42.0% for rhinitis, and 28.1% for eczema. The prevalence of SHS incursion into the children’s homes was 61.6%. In a multivariable logistic regression analysis adjusted for demographic and home environmental factors, children living in homes with SHS incursion (either no more than once a month or more than once a month) were more likely to have current wheeze, rhinitis, and eczema than those with no SHS incursion. Conclusions More than half of the children’s homes in MUH without smokers had SHS incursion. SHS incursion into homes was associated with wheeze, rhinitis, and eczema symptoms in children. Implications Children living in multi-unit housing (MUH) can be exposed to secondhand smoke (SHS) from smoke transferred from neighboring units with smokers. This study found that more than half of the children’s homes without smokers in MUH had SHS incursion. Children living in homes with SHS incursion (either no more than once a month or more than once a month) were more likely to have current wheeze, rhinitis, and eczema than those with no SHS incursion. We confirmed that SHS incursion was associated with allergic symptoms in children. Introduction Secondhand smoke (SHS), also known as passive smoking and environmental tobacco smoke, contains a complex mixture of over 7000 chemicals, including 69 known carcinogens.1 It was estimated that more than 41000 adult and approximately 900 infant deaths were attributed to SHS in the United States in 2006.2 In the same year, the US Surgeon General concluded that there are no risk-free levels of SHS exposure and that complete elimination of indoor smoking is the only way to protect nonsmokers from SHS exposure.3 Many countries have implemented smoke-free regulations in enclosed public places to reduce SHS exposure. However, implementation of smoke-free regulations has not been applied to personal living spaces. Children are particularly at risk of SHS exposure at home because they spend a large proportion of their time in the home environment. A previous study reported that nearly half of children (42.5%) worldwide were exposed to SHS in their homes.4 The two main factors for SHS exposure in children at home were smoking by parents or caregivers and smoking inside the home.5 SHS exposure in children has been associated with allergic diseases. Epidemiological studies showed that SHS exposure during pregnancy and early childhood was associated with increased risk of asthma and other respiratory symptoms including wheeze, cough, and respiratory infections.6 Data from phase three of the International Study of Asthma and Allergies in Childhood (ISAAC) showed an association between parental smoking and asthma symptoms in children.7 SHS was also associated with rhinitis8,9 and eczema symptoms.7,10,11 A recent systematic review showed that allergic rhinitis (pooled relative risk [RR] = 1.40, 95% confidence interval [CI] = 1.24 to 1.59) and eczema (pooled RR = 1.06, 95% CI = 1.01 to 1.11) were associated with SHS exposure in children and adolescents.12 Even in smoke-free homes, children living in multi-unit housing (MUH) could be exposed to SHS from smoke transferred from neighboring units with smokers,13 known as “SHS incursion.” A total of 44.0%–46.2% of American14 and 28.2% of Danish adults15 living in nonsmoking homes of MUH experienced SHS incursion into their home from another unit. In Seoul, Korea, 74.7% of MUH residents living in smoke-free homes experienced SHS incursion.16 Blood serum cotinine concentrations measured in American children living in homes in which no one smoked were higher in children living in apartments than in those living in detached houses.17 The relationship between SHS exposure from SHS incursion into homes and health effects in children has not been well established. Only one study in Hong Kong has reported that SHS incursion into homes without smokers was significantly associated with respiratory symptoms in adolescents.18 The present study investigated the relationship between SHS incursion and allergic symptoms in children living in MUH homes without smokers. Methods Study Design and Participants The results were based on the Atopy Free School in collaboration with the Seoul Atopy Asthma Information Center in Korean Center for Disease Control and Prevention and in Seoul Metropolitan Government. The cross-sectional study was conducted from May to September 2015 in Seoul, Korea. The target population consisted of children who were attending elementary schools, kindergartens, and daycare centers. The total number of eligible participants was 56336 children in 492 facilities. A newsletter containing a written consent form and questionnaires was delivered by the children to their parents or guardians asking if they wished to voluntarily participate in the study. Among these participants, filled-out questionnaires from 38150 children in 430 facilities were submitted (response rate of 67.7%). The study was approved by Seoul Medical Center’s institutional review board (IRB no. 2015-052). The study included children living in MUH, including attached housing and apartments. Attached housing was defined as multi-family housing including multi-household housing or row/multiplex housing of fewer than five stories. Apartments were defined as high-rise, multi-family buildings of five or more stories. Children living in detached housing and nonresidential buildings were not included because of logistical reasons as well as small sample size. Among 38150 children, those who answered questions related to individual factors such as sex, age, parental history of allergic diseases, breastfeeding, duration of residency, housing type, and allergic symptoms and those related to home environmental factors including SHS incursion were included for further analysis (n = 35831). The children were categorized using the following criteria: those living in (1) attached housing or apartments (n = 33174); (2) homes without smokers (n = 20481); and (3) homes for longer than 1 year (n = 16676). Children living in homes without smokers were identified by the response “no” to the following question: “Are there any current smokers in your home, including yourself?” Data from 16676 children between 1 and 13 years of age living in homes without smokers in MUH were included in the final analysis. Measurements The ISAAC core module was used to assess allergic symptoms in the children.19 Similar questions have been used in previous studies.20 Prevalence of wheeze, rhinitis, and eczema during the previous 12 months (current wheeze, rhinitis, and eczema) was determined by the official Korean version of the ISAAC questionnaires. A child with current wheeze was identified by the response “yes” to the question “Has your child had wheezing or whistling in the chest in the last 12 months?” A child with current rhinitis was identified by the response “yes” to the question “Has your child had a problem with sneezing or a runny or blocked nose when he/she did not have a cold or the flu in the past 12 months?” A child with current eczema was identified by the response “yes” to the question “Has your child had an itchy rash at any time in the last 12 months?” To examine the prevalence of SHS incursion into the children’s homes, respondents were asked how often they could smell tobacco smoke that had entered their living space from somewhere else in or around their building during the previous 12-month period. This question was based on a similar one used in a previous study.21 Respondents chose one of the following answer: “Never,” “Once a month or less,” “Twice a month,” “Four times a month,” “Two to four times a week,” or “Every day.” We also asked questions, obtained from previous studies, regarding several associated factors for allergic disease.11,22,23 We obtained information on the children’s demographic factors, including age, sex, parental history of allergic disease (any diagnoses of allergic disease by a doctor in either vs neither parent), breastfeeding, duration of residency, and housing type, and on the children’s home environmental factors, including whether any remodeling or purchase of new furniture had taken place in the previous 12 months in the home, presence of any mold spots inside the home, and traffic density near the home. Statistical Analysis The frequency of SHS incursion into homes was classified into three categories (none, SHS incursion no more than once a month, and SHS incursion more than once a month) with similar proportions before statistical analysis. A chi-square test was used to compare the prevalence of current wheeze, rhinitis, or eczema in the children with demographic and home environmental factors and to compare the frequency of SHS incursion with the housing type. Multivariable logistic regression models were used to determine the relationships between SHS incursion and current wheeze, rhinitis, and eczema in children after controlling for independent variables identified in the chi-square test. We included sex in the multivariable model because sex was important potential factors that affect the observed associations. Linear trend tests were performed by including frequency of SHS incursion as continuous variables in the multivariable model. The relationships between current wheeze, rhinitis, or eczema and the demographic and home variables were presented as adjusted odds ratios (aORs) with 95% CIs. A p value of <.05 was deemed as significant in all analyses. SAS software (ver. 9.2; SAS Institute, Inc, Cary, NC) was used for all statistical analyses. Results The average age of all 16676 children residing in homes without smokers in MUH was 5.6 ± 2.8 years. The prevalence of current allergic symptoms in the children was 4.9% for wheeze, 42.0% for rhinitis, and 28.1% for current eczema. The prevalence of current wheeze, rhinitis, and eczema significantly differed according to SHS incursion (p < .001) (Table 1). Table 1. Prevalence of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers According to Demographic and Home Environmental Factors   Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)      Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)    SHS = secondhand smoke. View Large Table 1. Prevalence of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers According to Demographic and Home Environmental Factors   Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)      Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)    SHS = secondhand smoke. View Large Overall, 61.6% of the parents or guardians of the children living in homes without smokers reported that they had experienced SHS incursion more than once in the past 12 months. SHS incursion was higher among children living in attached housing (62.4%) than among those in apartments (61.3%). The prevalence of SHS incursion differed significantly depending on the housing type (p < .001). Table 2 shows the results of multivariable logistic regression analyses of current wheeze, rhinitis, and eczema in children according to demographic and home environmental factors. Several demographic and home environmental factors were significantly associated with current wheeze, rhinitis, and eczema. In particular, children living in homes with SHS incursion (either no more than once a month or more than once a month) were more likely to have current wheeze (aOR = 1.21, 95% CI = 1.01 to 1.46; aOR = 1.46, 95% CI = 1.24 to 1.74, p for trend <.001), rhinitis (aOR = 1.22, 95% CI = 1.12 to 1.32; aOR = 1.38, 95% CI = 1.28 to 1.49, p for trend <.001), and eczema (aOR = 1.25, 95% CI = 1.15 to 1.37; aOR = 1.41, 95% CI = 1.30 to 1.53, p for trend <.001) than those with no SHS incursion. Table 2. Multivariable Logistic Regression Analysis of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers   Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001      Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001    Variables identified in the chi-square test (p < .05) and sex were included in the multivariable analysis. Bold estimates are statistically significant at p < .05. aOR = adjusted odds ratio; CI = confidence interval; SHS = secondhand smoke. View Large Table 2. Multivariable Logistic Regression Analysis of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers   Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001      Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001    Variables identified in the chi-square test (p < .05) and sex were included in the multivariable analysis. Bold estimates are statistically significant at p < .05. aOR = adjusted odds ratio; CI = confidence interval; SHS = secondhand smoke. View Large Discussion The prevalence of current wheeze, rhinitis, and eczema among children was slightly different compared with that in a previous study conducted in Seoul in 2012.20 The prevalence of current wheeze was slightly lower, but that of current rhinitis and eczema was higher, compared with the earlier study in Seoul,20 which reported prevalence rates of 5.6%, 32.5%, and 17.7% for current wheeze, rhinitis, and eczema, respectively, in children aged 0–13 years. Recent studies of allergic disease based on nationwide populations from 2009 to 2014 in Korea reported a decreasing trend for the prevalence of asthma and eczema but an increasing trend for the prevalence of allergic rhinitis in children aged <10 years.24 Thus, the higher prevalence of current rhinitis in the present study might be because of this increasing trend in allergic rhinitis among Korean children. The higher prevalence of eczema in the present study could be explained by the definition of eczema used in the questionnaires in our study. In the 2012 study in Seoul,20 for the diagnosis of eczema, patients were asked if they ever had an itchy rash intermittently for at least 6 months and then were further asked if they had experienced an itchy rash at any time during the previous 12 months. In the present study, the children were asked only if they had experienced an itchy rash at any time during the previous 12 months. Thus, the prevalence of eczema, as defined by the response to this question, in the present study may be higher than that in the 2012 study. More than half of children’s homes had SHS incursion. The prevalence of SHS incursion was associated with housing type and was higher among children living in attached housing than among those in apartments. This indicates that more than half of the children living in MUH homes without smokers were at risk of SHS exposure due to incursion. The findings suggest that smoking in MUH should be restricted to reduce SHS incursion into homes. Because implementation of smoke-free regulations in MUH might be difficult, providing educational material to building owners and managers on the importance of implementing smoke-free policies may be the first step to smoke-free MUH.25 The prevalence of SHS incursion into homes in the present study was slightly lower than that in a previous study in Seoul among people living in MUH, and higher than that in a previous study in the United States. A population-based study in Seoul in 2015 showed that the prevalence of SHS incursion into homes of MUH with smoke-free rules was 74.7%, and the smoking rate of the respondents was 25.2%.16 In the United States in 2010, 44% of residents in MUH living in homes with personal smoke-free rules experienced SHS incursion, and the smoking rate of the respondents was 21.1%.26 The present study asked whether the children were living with smokers in the home, including the respondents. Thus, we were unable to estimate the smoking rate of the respondents in the study. The higher prevalence of SHS incursion in the present study might be because of the higher smoking rate in Seoul than in the United States; thus, more smokers may live in MUH homes, leading to the higher prevalence of SHS incursion in Seoul. In the multivariable analysis, several demographic and home environmental factors were significantly associated with allergic symptoms in the children. In particular, SHS incursion into homes was strongly associated with allergic symptoms in children. The relationship between SHS incursion and current wheeze, rhinitis, and eczema among children was dose-dependent even after adjustment for demographic and home environmental factors. The aOR of SHS incursion experienced more than once a month was greater for current wheeze than that for current rhinitis and eczema in children. This finding indicates that SHS incursion into homes was associated with current wheeze, rhinitis, and eczema among children living in MUH homes without smokers. SHS incursion into homes was classified into three categories to examine the dose-dependent relationships between allergic symptoms in children and SHS incursion. In previous studies, SHS incursion was used as a dichotomous dependent variable.21,26 When we evaluated SHS incursion as a dichotomized variable (Yes = 1 vs No = 0), we found that children living in homes with SHS incursion were more likely to have current wheeze (aOR = 1.35, 95% CI = 1.16 to 1.57), rhinitis (aOR = 1.30, 95% CI = 1.22 to 1.40), and eczema (aOR = 1.34, 95% CI = 1.24 to 1.44) in the multivariable analysis. Our findings were similar to those obtained using three categories for SHS incursion in the multivariable analysis. SHS exposure has been reported as a risk factor for allergic disease in children.7,8,10–12 Although we found significant associations between allergic symptoms in children and SHS incursion, we were unable to confirm that allergic symptoms were associated only with SHS exposure. Frequent SHS incursion might be associated with the exposure of children to SHS, but could also be associated with exposure to residual tobacco pollutants in homes. Infiltrated SHS pollutants can remain on surfaces and dust particles in homes and can be re-emitted and/or re-suspended into the air, which is referred to as third-hand smoke (THS).27 A previous study showed that indoor surface nicotine concentrations were higher in homes of MUH whose nonsmoking residents reported frequent SHS incursion than in those whose nonsmoking residents reported no or infrequent SHS incursion.28 Frequent SHS incursion may be associated with an increased risk of THS exposure, and this could have resulted in the associations with allergic symptoms observed among the children in our study. Furthermore, children may have been exposed to THS, because they lived in homes with smokers in the past. Further research is needed to evaluate the relationships of SHS and THS with allergic disease among children to distinguish the effects of SHS and THS exposure. This is the first study to examine the relationship between SHS incursion and allergic symptoms among children in MUH. We included several demographic and home environmental factors in the multivariable logistic model. The study included children of a wide range of ages (1–13 years) among a large population in Seoul. This study has several limitations. Because the study design was cross-sectional, we could not infer that SHS incursion were causally associated with allergic symptoms in children. It might not be representative of Seoul’s population, because recruitment of the study subjects did not involve a random sampling process. Because samples size was large, the null hypothesis might be more likely to be rejected. Although ISAAC core module was used to assess the allergic symptoms in children, misclassification may have occurred because it was developed for children 6 years or older. However, epidemiology studies have used ISAAC core questions to assess the risk of allergic disease in infants.29–31 Another limitation was that there might be residual confounding by unknown or unmeasured confounders although we included several demographic and home environmental factors. Data on the children, including demographic and home environmental factors, were obtained from parents or guardians of the children. This reporting may have produced variation and recall bias depending on the sensitivity of the respondents. In particular, we measured SHS incursion based on the detection of SHS odor by the children’s parents or guardians. Thus, we did not confirm or quantify the exposure to tobacco pollutants caused by SHS incursion. Although the use of specific biomarkers for SHS exposure (eg, cotinine) can give objective measurement, it cannot distinguish the sources and locations of exposure. The self-reported SHS incursion by MUH residents in smoke-free homes has been used as objective measurements in other studies.16,21 Before and after study using specific markers for SHS exposure might give a better understanding of the associations between SHS incursion and allergic disease among children. Conclusion We evaluated 16676 children living in MUH homes without smokers. More than half of the children’s homes had experienced SHS incursion in the previous 12 months. The high prevalence of SHS incursion into homes suggests that most children living in MUH may be at risk of pollutant exposure due to SHS incursion. Several demographic and home environmental factors were associated with current wheeze, rhinitis, and eczema among the children. In particular, the frequency of SHS incursion displayed a dose-dependent relationship with current wheeze, rhinitis, and eczema in children even after adjustment for demographic and home environmental factors. Our findings suggest that SHS incursion was associated with these allergic symptoms in children living in MUH homes without smokers. Implementation of smoke-free regulations in MUH is necessary to protect children from harms caused by SHS exposure due to incursion in their homes. Funding This study was supported by the Seoul Medical Center, Korea (15-A01). Declaration of Interests None declared. Acknowledgments The authors appreciate Korean Center for Disease Control and Prevention and Seoul Metropolitan Government for their support. The authors also would like to thank the Seoul Medical Center for supporting this study. References 1. US Department of Health and Human Services. How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General . 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Google Scholar CrossRef Search ADS PubMed  25. David S, Kevin C. Smoke-Free Multiunit Housing in Canada: Report Card on Cancer in Canada, 2011–2012 . Cancer Advocacy Coalition of Canada; 2012. http://www.canceradvocacy.ca/report-card-on-cancer-in-canada.pdf. Accessed October 31, 2017. 26. Licht AS, King BA, Travers MJ, Rivard C, Hyland AJ. Attitudes, experiences, and acceptance of smoke-free policies among US multiunit housing residents. Am J Public Health . 2012; 102( 10): 1868– 1871. doi: 10.2105/ajph.2012.300717. Google Scholar CrossRef Search ADS PubMed  27. Matt GE, Quintana PJ, Destaillats Het al.   Thirdhand tobacco smoke: emerging evidence and arguments for a multidisciplinary research agenda. Environ Health Perspect . 2011; 119( 9): 1218– 1226. doi: 10.1289/ehp.1103500. Google Scholar CrossRef Search ADS PubMed  28. Hood NE, Ferketich AK, Klein EG, Pirie P, Wewers ME. Associations between self-reported in-home smoking behaviours and surface nicotine concentrations in multiunit subsidised housing. Tob Control . 2014; 23( 1): 27– 32. doi: 10.1136/tobaccocontrol-2012-050666. Google Scholar CrossRef Search ADS PubMed  29. Wijga AH, Smit HA, Kerkhof Met al.  ; PIAMA. Association of consumption of products containing milk fat with reduced asthma risk in pre-school children: the PIAMA birth cohort study. Thorax . 2003; 58( 7): 567– 572. doi: 10.1136/thorax.58.7.567. Google Scholar CrossRef Search ADS PubMed  30. Snijders BE, Thijs C, Kummeling I, Penders J, van den Brandt PA. Breastfeeding and infant eczema in the first year of life in the KOALA birth cohort study: a risk period-specific analysis. Pediatrics . 2007; 119( 1): e137– e141. doi: 10.1542/peds.2006-0772. Google Scholar CrossRef Search ADS PubMed  31. Morais-Almeida M, Santos N, Pereira AMet al.   Prevalence and classification of rhinitis in preschool children in Portugal: a nationwide study. Allergy . 2013; 68( 10): 1278– 1288. doi: 10.1111/all.12221. Google Scholar CrossRef Search ADS PubMed  © The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Nicotine and Tobacco Research Oxford University Press

Relationships Between Secondhand Smoke Incursion and Wheeze, Rhinitis, and Eczema Symptoms in Children Living in Homes Without Smokers in Multi-Unit Housing

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Abstract

Abstract Introduction Secondhand smoke (SHS) incursion can occur in units of multi-unit housing (MUH). The purpose of this study was to determine the relationship between SHS incursion and allergic symptoms in children living in MUH without smokers. Methods We conducted a cross-sectional study from May to September 2015 in Seoul, Korea. Children were recruited from elementary schools, kindergartens, and daycare centers. In total, 16676 children between 1 and 13 years of age living in MUH without smokers were included in the analysis. Allergic symptoms during the previous 12 months (current wheeze, rhinitis, and eczema) and home environmental factors, including the frequency of SHS incursion during the previous 12 months, were examined using a questionnaire filled out by the parents or guardians of the children. Results The prevalence of current allergic symptoms in children was 4.9% for wheeze, 42.0% for rhinitis, and 28.1% for eczema. The prevalence of SHS incursion into the children’s homes was 61.6%. In a multivariable logistic regression analysis adjusted for demographic and home environmental factors, children living in homes with SHS incursion (either no more than once a month or more than once a month) were more likely to have current wheeze, rhinitis, and eczema than those with no SHS incursion. Conclusions More than half of the children’s homes in MUH without smokers had SHS incursion. SHS incursion into homes was associated with wheeze, rhinitis, and eczema symptoms in children. Implications Children living in multi-unit housing (MUH) can be exposed to secondhand smoke (SHS) from smoke transferred from neighboring units with smokers. This study found that more than half of the children’s homes without smokers in MUH had SHS incursion. Children living in homes with SHS incursion (either no more than once a month or more than once a month) were more likely to have current wheeze, rhinitis, and eczema than those with no SHS incursion. We confirmed that SHS incursion was associated with allergic symptoms in children. Introduction Secondhand smoke (SHS), also known as passive smoking and environmental tobacco smoke, contains a complex mixture of over 7000 chemicals, including 69 known carcinogens.1 It was estimated that more than 41000 adult and approximately 900 infant deaths were attributed to SHS in the United States in 2006.2 In the same year, the US Surgeon General concluded that there are no risk-free levels of SHS exposure and that complete elimination of indoor smoking is the only way to protect nonsmokers from SHS exposure.3 Many countries have implemented smoke-free regulations in enclosed public places to reduce SHS exposure. However, implementation of smoke-free regulations has not been applied to personal living spaces. Children are particularly at risk of SHS exposure at home because they spend a large proportion of their time in the home environment. A previous study reported that nearly half of children (42.5%) worldwide were exposed to SHS in their homes.4 The two main factors for SHS exposure in children at home were smoking by parents or caregivers and smoking inside the home.5 SHS exposure in children has been associated with allergic diseases. Epidemiological studies showed that SHS exposure during pregnancy and early childhood was associated with increased risk of asthma and other respiratory symptoms including wheeze, cough, and respiratory infections.6 Data from phase three of the International Study of Asthma and Allergies in Childhood (ISAAC) showed an association between parental smoking and asthma symptoms in children.7 SHS was also associated with rhinitis8,9 and eczema symptoms.7,10,11 A recent systematic review showed that allergic rhinitis (pooled relative risk [RR] = 1.40, 95% confidence interval [CI] = 1.24 to 1.59) and eczema (pooled RR = 1.06, 95% CI = 1.01 to 1.11) were associated with SHS exposure in children and adolescents.12 Even in smoke-free homes, children living in multi-unit housing (MUH) could be exposed to SHS from smoke transferred from neighboring units with smokers,13 known as “SHS incursion.” A total of 44.0%–46.2% of American14 and 28.2% of Danish adults15 living in nonsmoking homes of MUH experienced SHS incursion into their home from another unit. In Seoul, Korea, 74.7% of MUH residents living in smoke-free homes experienced SHS incursion.16 Blood serum cotinine concentrations measured in American children living in homes in which no one smoked were higher in children living in apartments than in those living in detached houses.17 The relationship between SHS exposure from SHS incursion into homes and health effects in children has not been well established. Only one study in Hong Kong has reported that SHS incursion into homes without smokers was significantly associated with respiratory symptoms in adolescents.18 The present study investigated the relationship between SHS incursion and allergic symptoms in children living in MUH homes without smokers. Methods Study Design and Participants The results were based on the Atopy Free School in collaboration with the Seoul Atopy Asthma Information Center in Korean Center for Disease Control and Prevention and in Seoul Metropolitan Government. The cross-sectional study was conducted from May to September 2015 in Seoul, Korea. The target population consisted of children who were attending elementary schools, kindergartens, and daycare centers. The total number of eligible participants was 56336 children in 492 facilities. A newsletter containing a written consent form and questionnaires was delivered by the children to their parents or guardians asking if they wished to voluntarily participate in the study. Among these participants, filled-out questionnaires from 38150 children in 430 facilities were submitted (response rate of 67.7%). The study was approved by Seoul Medical Center’s institutional review board (IRB no. 2015-052). The study included children living in MUH, including attached housing and apartments. Attached housing was defined as multi-family housing including multi-household housing or row/multiplex housing of fewer than five stories. Apartments were defined as high-rise, multi-family buildings of five or more stories. Children living in detached housing and nonresidential buildings were not included because of logistical reasons as well as small sample size. Among 38150 children, those who answered questions related to individual factors such as sex, age, parental history of allergic diseases, breastfeeding, duration of residency, housing type, and allergic symptoms and those related to home environmental factors including SHS incursion were included for further analysis (n = 35831). The children were categorized using the following criteria: those living in (1) attached housing or apartments (n = 33174); (2) homes without smokers (n = 20481); and (3) homes for longer than 1 year (n = 16676). Children living in homes without smokers were identified by the response “no” to the following question: “Are there any current smokers in your home, including yourself?” Data from 16676 children between 1 and 13 years of age living in homes without smokers in MUH were included in the final analysis. Measurements The ISAAC core module was used to assess allergic symptoms in the children.19 Similar questions have been used in previous studies.20 Prevalence of wheeze, rhinitis, and eczema during the previous 12 months (current wheeze, rhinitis, and eczema) was determined by the official Korean version of the ISAAC questionnaires. A child with current wheeze was identified by the response “yes” to the question “Has your child had wheezing or whistling in the chest in the last 12 months?” A child with current rhinitis was identified by the response “yes” to the question “Has your child had a problem with sneezing or a runny or blocked nose when he/she did not have a cold or the flu in the past 12 months?” A child with current eczema was identified by the response “yes” to the question “Has your child had an itchy rash at any time in the last 12 months?” To examine the prevalence of SHS incursion into the children’s homes, respondents were asked how often they could smell tobacco smoke that had entered their living space from somewhere else in or around their building during the previous 12-month period. This question was based on a similar one used in a previous study.21 Respondents chose one of the following answer: “Never,” “Once a month or less,” “Twice a month,” “Four times a month,” “Two to four times a week,” or “Every day.” We also asked questions, obtained from previous studies, regarding several associated factors for allergic disease.11,22,23 We obtained information on the children’s demographic factors, including age, sex, parental history of allergic disease (any diagnoses of allergic disease by a doctor in either vs neither parent), breastfeeding, duration of residency, and housing type, and on the children’s home environmental factors, including whether any remodeling or purchase of new furniture had taken place in the previous 12 months in the home, presence of any mold spots inside the home, and traffic density near the home. Statistical Analysis The frequency of SHS incursion into homes was classified into three categories (none, SHS incursion no more than once a month, and SHS incursion more than once a month) with similar proportions before statistical analysis. A chi-square test was used to compare the prevalence of current wheeze, rhinitis, or eczema in the children with demographic and home environmental factors and to compare the frequency of SHS incursion with the housing type. Multivariable logistic regression models were used to determine the relationships between SHS incursion and current wheeze, rhinitis, and eczema in children after controlling for independent variables identified in the chi-square test. We included sex in the multivariable model because sex was important potential factors that affect the observed associations. Linear trend tests were performed by including frequency of SHS incursion as continuous variables in the multivariable model. The relationships between current wheeze, rhinitis, or eczema and the demographic and home variables were presented as adjusted odds ratios (aORs) with 95% CIs. A p value of <.05 was deemed as significant in all analyses. SAS software (ver. 9.2; SAS Institute, Inc, Cary, NC) was used for all statistical analyses. Results The average age of all 16676 children residing in homes without smokers in MUH was 5.6 ± 2.8 years. The prevalence of current allergic symptoms in the children was 4.9% for wheeze, 42.0% for rhinitis, and 28.1% for current eczema. The prevalence of current wheeze, rhinitis, and eczema significantly differed according to SHS incursion (p < .001) (Table 1). Table 1. Prevalence of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers According to Demographic and Home Environmental Factors   Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)      Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)    SHS = secondhand smoke. View Large Table 1. Prevalence of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers According to Demographic and Home Environmental Factors   Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)      Total  Current wheeze  Current rhinitis  Current eczema  Yes (%)  p  Yes (%)  p  Yes (%)  p  Age (years)   1–3  4522  388 (8.6)  <.001  1599 (35.4)  <.001  1490 (33.0)  <.001   4–6  6779  281 (4.1)    2965 (43.7)    1976 (29.1)     7–9  3131  101 (3.2)    1427 (45.6)    754 (24.1)     10–13  2244  50 (2.2)    1007 (44.9)    459 (2 .5)    Sex   Female  8179  332 (4.1)  <.001  3079 (37.6)  <.001  2341 (28.6)  .112   Male  8497  488 (5.7)    3919 (46.1)    2338 (27.5)    Parental history of allergic disease   No  8492  289 (3.4)  <.001  2411 (28.4)  <.001  1785 (21.0)  <.001   Yes  8184  531 (6.5)    4587 (56.0)    2894 (35.4)    Breastfeeding   No  3424  165 (4.8)  .765  1448 (42.3)  .665  848 (24.8)  <.001   Yes  13252  655 (4.9)    5550 (41.9)    3831 (28.9)    Duration of residency (years)   <2  3413  198 (5.8)  .002  1429 (41.9)  .467  965 (28.3)  .003   2–4  6337  336 (5.3)    2626 (41.4)    1862 (29.4)     ≥5  6926  286 (4.1)    2943 (42.5)    1852 (26.7)    Housing type   Attached housing  4985  266 (5.3)  .103  1950 (39.1)  <.001  1399 (28.1)  .991   Apartment  11691  554 (4.7)    5048 (43.2)    3280 (28.1)    Remodeling   No  14734  707 (4.8)  .051  6136 (41.6)  .021  4094 (27.8)  .031   Yes  1942  113 (5.8)    862 (44.4)    585 (3 .1)    New furniture   No  12249  595 (4.9)  .553  5028 (41.0)  <.001  3284 (26.8)  <.001   Yes  4427  225 (5.1)    1970 (44.5)    1395 (31.5)    Mold spots   No  8907  361 (4.1)  <.001  3475 (39.0)  <.001  2226 (25.0)  <.001   Yes  7769  459 (5.9)    3523 (45.3)    2453 (31.6)    Traffic density   Light  3143  139 (4.4)  .141  1219 (38.8)  <.001  796 (25.3)  <.001   Moderate  7476  359 (4.8)    3045 (4 .7)    2042 (27.3)     Heavy  6057  322 (5.3)    2734 (45.1)    1841 (3 .4)    SHS incursion (times/month)   None  6401  253 (4.0)  <.001  2328 (36.4)  <.001  1512 (23.6)  <.001   ≤1  4565  229 (5.0)    1979 (43.4)    1336 (29.3)     >1  5710  338 (5.9)    2691 (47.1)    1831 (32.1)    SHS = secondhand smoke. View Large Overall, 61.6% of the parents or guardians of the children living in homes without smokers reported that they had experienced SHS incursion more than once in the past 12 months. SHS incursion was higher among children living in attached housing (62.4%) than among those in apartments (61.3%). The prevalence of SHS incursion differed significantly depending on the housing type (p < .001). Table 2 shows the results of multivariable logistic regression analyses of current wheeze, rhinitis, and eczema in children according to demographic and home environmental factors. Several demographic and home environmental factors were significantly associated with current wheeze, rhinitis, and eczema. In particular, children living in homes with SHS incursion (either no more than once a month or more than once a month) were more likely to have current wheeze (aOR = 1.21, 95% CI = 1.01 to 1.46; aOR = 1.46, 95% CI = 1.24 to 1.74, p for trend <.001), rhinitis (aOR = 1.22, 95% CI = 1.12 to 1.32; aOR = 1.38, 95% CI = 1.28 to 1.49, p for trend <.001), and eczema (aOR = 1.25, 95% CI = 1.15 to 1.37; aOR = 1.41, 95% CI = 1.30 to 1.53, p for trend <.001) than those with no SHS incursion. Table 2. Multivariable Logistic Regression Analysis of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers   Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001      Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001    Variables identified in the chi-square test (p < .05) and sex were included in the multivariable analysis. Bold estimates are statistically significant at p < .05. aOR = adjusted odds ratio; CI = confidence interval; SHS = secondhand smoke. View Large Table 2. Multivariable Logistic Regression Analysis of Current Wheeze, Rhinitis, and Eczema in Children Living in Homes Without Smokers   Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001      Current wheeze  Current rhinitis  Current eczema  aOR (95% CI)  p  aOR (95% CI)  p  aOR (95% CI)  p  Age (years) (continuous)  0.83 (0.81–0.86)  <.001  1.07 (1.05–1.08)  <.001  0.93 (0.92–0.94)  <.001  Sex   Female  1.00    1.00    1.00     Male  1.44 (1.24–1.66)  <.001  1.45 (1.36–1.55)  <.001  0.94 (0.88–1.01)  .073  Parental history of allergic disease   No  1.00    1.00    1.00     Yes  1.81 (1.56–2.10)  <.001  3.17 (2.97–3.38)  <.001  1.93 (1.80–2.07)  <.001  Breastfeeding   No          1.00     Yes          1.14 (1.05–1.25)  .003  Duration of residency (years)   <2  1.00        1.00     2–4  0.87 (0.72–1.04)  .128      1.03 (0.94–1.14)  .509   ≥5  0.79 (0.66–0.96)  .017      0.97 (0.88–1.06)  .466  Housing type   Attached housing      1.00         Apartment      1.17 (1.09–1.26)  <.001      Remodeling               No      1.00    1.00     Yes      1.01 (0.91–1.12)  .832  1.02 (0.92–1.14)  .710  New furniture   No      1.00    1.00     Yes      1.10 (1.02–1.18)  .017  1.19 (1.10–1.28)  <.001  Mold spots   No  1.00    1.00    1.00     Yes  1.32 (1.14–1.53)  <.001  1.23 (1.15–1.31)  <.001  1.26 (1.17–1.35)  <.001  Traffic density   Light      1.00    1.00     Moderate      1.06 (0.97–1.16)  .240  1.09 (0.99–1.20)  .076   Heavy      1.18 (1.07–1.29)  <.001  1.19 (1.08–1.32)  .001  SHS incursion (times/month)   None  1.00    1.00    1.00     ≤1  1.21 (1.01–1.46)  .043  1.22 (1.12–1.32)  <.001  1.25 (1.15–1.37)  <.001   >1  1.46 (1.24–1.74)  <.001  1.38 (1.28–1.49)  <.001  1.41 (1.30–1.53)  <.001   p for trend  <.001    <.001    <.001    Variables identified in the chi-square test (p < .05) and sex were included in the multivariable analysis. Bold estimates are statistically significant at p < .05. aOR = adjusted odds ratio; CI = confidence interval; SHS = secondhand smoke. View Large Discussion The prevalence of current wheeze, rhinitis, and eczema among children was slightly different compared with that in a previous study conducted in Seoul in 2012.20 The prevalence of current wheeze was slightly lower, but that of current rhinitis and eczema was higher, compared with the earlier study in Seoul,20 which reported prevalence rates of 5.6%, 32.5%, and 17.7% for current wheeze, rhinitis, and eczema, respectively, in children aged 0–13 years. Recent studies of allergic disease based on nationwide populations from 2009 to 2014 in Korea reported a decreasing trend for the prevalence of asthma and eczema but an increasing trend for the prevalence of allergic rhinitis in children aged <10 years.24 Thus, the higher prevalence of current rhinitis in the present study might be because of this increasing trend in allergic rhinitis among Korean children. The higher prevalence of eczema in the present study could be explained by the definition of eczema used in the questionnaires in our study. In the 2012 study in Seoul,20 for the diagnosis of eczema, patients were asked if they ever had an itchy rash intermittently for at least 6 months and then were further asked if they had experienced an itchy rash at any time during the previous 12 months. In the present study, the children were asked only if they had experienced an itchy rash at any time during the previous 12 months. Thus, the prevalence of eczema, as defined by the response to this question, in the present study may be higher than that in the 2012 study. More than half of children’s homes had SHS incursion. The prevalence of SHS incursion was associated with housing type and was higher among children living in attached housing than among those in apartments. This indicates that more than half of the children living in MUH homes without smokers were at risk of SHS exposure due to incursion. The findings suggest that smoking in MUH should be restricted to reduce SHS incursion into homes. Because implementation of smoke-free regulations in MUH might be difficult, providing educational material to building owners and managers on the importance of implementing smoke-free policies may be the first step to smoke-free MUH.25 The prevalence of SHS incursion into homes in the present study was slightly lower than that in a previous study in Seoul among people living in MUH, and higher than that in a previous study in the United States. A population-based study in Seoul in 2015 showed that the prevalence of SHS incursion into homes of MUH with smoke-free rules was 74.7%, and the smoking rate of the respondents was 25.2%.16 In the United States in 2010, 44% of residents in MUH living in homes with personal smoke-free rules experienced SHS incursion, and the smoking rate of the respondents was 21.1%.26 The present study asked whether the children were living with smokers in the home, including the respondents. Thus, we were unable to estimate the smoking rate of the respondents in the study. The higher prevalence of SHS incursion in the present study might be because of the higher smoking rate in Seoul than in the United States; thus, more smokers may live in MUH homes, leading to the higher prevalence of SHS incursion in Seoul. In the multivariable analysis, several demographic and home environmental factors were significantly associated with allergic symptoms in the children. In particular, SHS incursion into homes was strongly associated with allergic symptoms in children. The relationship between SHS incursion and current wheeze, rhinitis, and eczema among children was dose-dependent even after adjustment for demographic and home environmental factors. The aOR of SHS incursion experienced more than once a month was greater for current wheeze than that for current rhinitis and eczema in children. This finding indicates that SHS incursion into homes was associated with current wheeze, rhinitis, and eczema among children living in MUH homes without smokers. SHS incursion into homes was classified into three categories to examine the dose-dependent relationships between allergic symptoms in children and SHS incursion. In previous studies, SHS incursion was used as a dichotomous dependent variable.21,26 When we evaluated SHS incursion as a dichotomized variable (Yes = 1 vs No = 0), we found that children living in homes with SHS incursion were more likely to have current wheeze (aOR = 1.35, 95% CI = 1.16 to 1.57), rhinitis (aOR = 1.30, 95% CI = 1.22 to 1.40), and eczema (aOR = 1.34, 95% CI = 1.24 to 1.44) in the multivariable analysis. Our findings were similar to those obtained using three categories for SHS incursion in the multivariable analysis. SHS exposure has been reported as a risk factor for allergic disease in children.7,8,10–12 Although we found significant associations between allergic symptoms in children and SHS incursion, we were unable to confirm that allergic symptoms were associated only with SHS exposure. Frequent SHS incursion might be associated with the exposure of children to SHS, but could also be associated with exposure to residual tobacco pollutants in homes. Infiltrated SHS pollutants can remain on surfaces and dust particles in homes and can be re-emitted and/or re-suspended into the air, which is referred to as third-hand smoke (THS).27 A previous study showed that indoor surface nicotine concentrations were higher in homes of MUH whose nonsmoking residents reported frequent SHS incursion than in those whose nonsmoking residents reported no or infrequent SHS incursion.28 Frequent SHS incursion may be associated with an increased risk of THS exposure, and this could have resulted in the associations with allergic symptoms observed among the children in our study. Furthermore, children may have been exposed to THS, because they lived in homes with smokers in the past. Further research is needed to evaluate the relationships of SHS and THS with allergic disease among children to distinguish the effects of SHS and THS exposure. This is the first study to examine the relationship between SHS incursion and allergic symptoms among children in MUH. We included several demographic and home environmental factors in the multivariable logistic model. The study included children of a wide range of ages (1–13 years) among a large population in Seoul. This study has several limitations. Because the study design was cross-sectional, we could not infer that SHS incursion were causally associated with allergic symptoms in children. It might not be representative of Seoul’s population, because recruitment of the study subjects did not involve a random sampling process. Because samples size was large, the null hypothesis might be more likely to be rejected. Although ISAAC core module was used to assess the allergic symptoms in children, misclassification may have occurred because it was developed for children 6 years or older. However, epidemiology studies have used ISAAC core questions to assess the risk of allergic disease in infants.29–31 Another limitation was that there might be residual confounding by unknown or unmeasured confounders although we included several demographic and home environmental factors. Data on the children, including demographic and home environmental factors, were obtained from parents or guardians of the children. This reporting may have produced variation and recall bias depending on the sensitivity of the respondents. In particular, we measured SHS incursion based on the detection of SHS odor by the children’s parents or guardians. Thus, we did not confirm or quantify the exposure to tobacco pollutants caused by SHS incursion. Although the use of specific biomarkers for SHS exposure (eg, cotinine) can give objective measurement, it cannot distinguish the sources and locations of exposure. The self-reported SHS incursion by MUH residents in smoke-free homes has been used as objective measurements in other studies.16,21 Before and after study using specific markers for SHS exposure might give a better understanding of the associations between SHS incursion and allergic disease among children. Conclusion We evaluated 16676 children living in MUH homes without smokers. More than half of the children’s homes had experienced SHS incursion in the previous 12 months. The high prevalence of SHS incursion into homes suggests that most children living in MUH may be at risk of pollutant exposure due to SHS incursion. Several demographic and home environmental factors were associated with current wheeze, rhinitis, and eczema among the children. In particular, the frequency of SHS incursion displayed a dose-dependent relationship with current wheeze, rhinitis, and eczema in children even after adjustment for demographic and home environmental factors. 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Nicotine and Tobacco ResearchOxford University Press

Published: Mar 6, 2018

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