Arch Virol (2007) 152: 1295–1303
Printed in The Netherlands
Inter-seasonal diversity of norovirus genotypes:
Emergence and selection of virus variants
C. I. Gallimore, M. Iturriza-Gomara, J. Xerry, J. Adigwe, and J. J. Gray
Centre for Infections, Health Protection Agency, Enteric Virus Unit, Virus Reference Department,
Colindale, London, U.K.
Received August 9, 2006; accepted February 7, 2007; published online March 15, 2007
# Springer-Verlag 2007
This study describes a method used to determine the
diversity of NoVs co-circulating in the community
that consisted of the analysis of a limited number of
strains collected from outbreaks occurring at differ-
ent times of the NoV season. The diversity of twenty
NoV strains collected from outbreaks occurring
at the beginning of each NoV season (September)
was compared to the diversity found in the middle
(December) and at the end of the season (March).
The method was validated through the characterisa-
tion of greater numbers of strains at times when nov-
el genotypes or variants were detected. A total of
864 strains from outbreaks of gastroenteritis from
the 2003=04, 2004=05 and 2005=06 seasons were
genotyped, with the majority of outbreaks occurring
in the UK.
There was a greater diversity of NoV genotypes at
the beginning of two of the three seasons, 2003=04
and 2005=06, when compared to strains circulat-
ing at the end of the seasons, and GII-4 NoV strains
predominated (>90%) at the end of each season.
Data from this study also identiﬁed the co-circulation
and differentiation of three major GII-4 variants
(v2, v3, and v4). Detailed analysis of a larger num-
ber of strains throughout each season conﬁrmed
that variants emerged, became the predominant cir-
culating strain and were ultimately replaced with
another variant selected from a pool of variants.
By June 2006, GII-4 v4 (Hu=NoV=Rhyl440=2005=
UK) emerged as the predominant GII-4 strain,
usurping the previous GII-4 v3 strain [Hu=NoV=
Hunter284E=040=AU] to become the commonest
co-circulating strain, in the UK in 2006.
Noroviruses (NoVs) are members of the family
Caliciviridae  and are the commonest cause of
outbreaks of acute gastroenteritis world-wide .
NoV outbreaks are frequently associated with semi-
closed or closed institutions such as hospitals 
and homes for the elderly . Outbreaks also occur
in other settings, including eating establishments
, cruise ships , concert halls  and schools
. Transmission of NoVs is usually by person-to-
person spread , although food [1, 7, 20], includ-
ing shellﬁsh , water , and environmental or
airborne contamination have all been implicated in
transmission [8, 11, 25].
Author’s address: Chris I. Gallimore, Centre for Infec-
tions, Enteric Virus Unit, Virus Reference Department,
Health Protection Agency, Colindale, London, NW9 5HT,
U.K. e-mail: firstname.lastname@example.org