[You can find Informational links on the Norovirus along the right side-bar of the blog]
January 25, 2013 / 62(03);55-55
Noroviruses are the leading cause of epidemic gastroenteritis, including foodborne outbreaks, in the United States (
1).
Hospitalization and mortality associated with norovirus infection occur
most frequently among elderly persons, young children, and
immunocompromised patients. Noroviruses belong to the family
Caliciviridae
and can be grouped into five genogroups (GI through GV), which are
further divided into at least 34 genotypes. Human disease primarily is
caused by GI and GII noroviruses, with most outbreaks caused by GII.4
strains (
1).
During the past decade, new GII.4 strains have emerged every 2–3 years,
replacing previously predominant GII.4 strains. Emergence of these new
norovirus strains has often, but not always, led to increased outbreak
activity. For example, the previously dominant GII.4 New Orleans strain
was not associated with increased norovirus outbreak activity in the
United States (
2). CDC collects information on norovirus strains
associated with outbreaks in the United States through an electronic
laboratory surveillance network called CaliciNet (
3). This report
documents the recent emergence of a new GII.4 strain, GII.4 Sydney,
which caused most (53%) of the norovirus outbreaks reported through
CaliciNet during September–December 2012. Continued surveillance will
enable further assessment of the public health implications and
significance of this new strain.
In March 2012, a new GII.4 norovirus strain was identified in
Australia. Named GII.4 Sydney, this emergent strain has since caused
acute gastroenteritis outbreaks in multiple countries (
4). In the
United Kingdom, an early onset of the 2012 winter norovirus season was
reported in association with emergence of GII.4 Sydney as the dominant
strain implicated in
outbreaks.* In
the United States, GII.4 Sydney has spread rapidly nationwide, causing
an increasing number of outbreaks. During September–December 2012, a
total of 141 (53%) of the 266 norovirus outbreaks reported to CaliciNet
were caused by GII.4 Sydney. The other outbreaks were caused by 10
different GI and GII genotypes, including GII.4 New Orleans. A
statistically significant increase in the proportion of outbreaks caused
by GII.4 Sydney was noted: four (19%) of 21 outbreaks in September
2012; 22 (46%) of 48 in October 2012; 70 (58%) of 120 in November 2012;
and 45 (58%) of 77 in
December 2012†
(chi-square test for trend; p<0.01). Most (72 [51%]) of these GII.4
Sydney outbreaks resulted from direct person-to-person transmission; 29
(20%) were foodborne, one (1%) was waterborne, and the transmission mode
was unknown in 39 (28%) of the outbreaks. Long-term–care facilities and
restaurants were the most frequently reported settings, accounting for
91 (65%) and 18 (13%) of the GII.4 Sydney outbreaks, respectively.
During the three previous winters, the peak in reported norovirus
outbreaks occurred in January; therefore, at present, it is too early to
make an assessment of the relative magnitude of the current season.
GII.4 noroviruses remain the predominant cause of norovirus
outbreaks, and the GII.4 Sydney strain appears to have replaced the
previously predominant strain, GII.4 New Orleans. Compared with other
norovirus genotypes, GII.4 noroviruses have been associated with
increased rates of hospitalizations and deaths during outbreaks (
5).
Health-care providers and public health practitioners should remain
vigilant to the potential for increased norovirus activity in the
ongoing season related to the emergent GII.4 Sydney strain. Continued
surveillance for norovirus outbreaks through CaliciNet and additional
data on clinical and epidemiologic features of outbreaks collected
through the National Outbreak Reporting System
(NORS)§
will enable further assessment of the public health implications of the
new GII.4 Sydney strain, including any association with increased
severity or level of activity in the ongoing 2012–13 winter norovirus
season. Proper hand hygiene, environmental disinfection, and isolation
of ill persons remain the mainstays of norovirus prevention and control (
1).
Reported by
Leslie Barclay, Mary Wikswo, MPH, Nicole Gregoricus, MSPH, Jan
Vinjé, PhD, Ben Lopman, PhD, Umesh Parashar, MBBS, Aron Hall, DVM, Div
of Viral Diseases, National Center for Immunization and Respiratory
Diseases; Eyal Leshem, MD, EIS officer, CDC. Corresponding contributor: Eyal Leshem, eleshem@cdc.gov, 404-639-7251.
References
- CDC. Updated norovirus outbreak management and disease prevention guidelines. MMWR 2011;60(No. RR-3).
- Yen C, Wikswo ME, Lopman BA, Vinje J, Parashar UD, Hall AJ.
Impact of an emergent norovirus variant in 2009 on norovirus outbreak
activity in the United States. Clin Infect Dis 2011;53:568–71.
- Vega E, Barclay L, Gregoricus N, Williams K, Lee D, Vinje J.
Novel surveillance network for norovirus gastroenteritis outbreaks,
United States. Emerg Infect Dis 2011;17:1389–95.
- van Beek J, Ambert-Balay K, Botteldoorn N, et al. Indications
for worldwide increased norovirus activity associated with emergence of a
new variant of genotype II.4, late 2012. Euro Surveill 2013;18(1).
- Desai R, Hembree CD, Handel A, et al. Severe outcomes are
associated with genogroup 2 genotype 4 norovirus outbreaks: a systematic
literature review. Clin Infect Dis 2012;55:189–93.