Published Date: 2006-06-03 00:00:00
Subject: PRO/EDR> Norovirus - Canada (Calgary)
Archive Number: 20060603.1547
NOROVIRUS - CANADA (CALGARY)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Sat 3 Jun 2006
From: Pablo Nart <email@example.com>
Source: Calgary Herald, Fri 2 Jun 2006 [edited]
Calgary experienced an unprecedented number of norovirus outbreaks
this May, with nearly a dozen identified instances of the stomach bug
that is more common in the winter months.
Calgary Health Region (CHR) officials announced on Friday [2 Jun
2006] that they confirmed 11 outbreaks of Norovirus affecting 192
people in May in settings that range from long-term care homes to
restaurants. Experts say they normally see only a handful of
norovirus -- which causes nausea, vomiting and diarrhea -- during the
spring and summer months.
"This is unusual," said Dr. Judy MacDonald, deputy medical officer of
health for CHR, who wanted to alert the public to the outbreaks,
although they are usually not serious. "We've seen what I would call
unprecedented norovirus activity in May."
Officials say the higher-than-usual number of cases may be linked to
the summer travel season, noting that some cruise ships and trains
have recently had problems with norovirus outbreaks.
The virus is also thought to occur in 2-year cycles, with 2004 being
the last year with a significant number of outbreaks in Calgary.
Indeed, the month with the largest number of outbreaks was November
2004 when Calgary's downtown Drop-In Centre saw 140 clients and staff
infected with the [virus]. Parts of the facility were quarantined for
nearly 3 weeks.
On Friday, CHR officials did not identify any facilities affected by
the most recent outbreaks. Although there were 11 confirmed outbreaks
of norovirus in May 2006, MacDonald says that is likely a fraction of
the number of cases that are actually in Calgary. She noted that the
number of Calgarians calling the CHR's healthlink number complaining
of gastrointestinal illnesses has increased in recent weeks.
[Noroviruses are enteric viruses belonging to the family
_Caliciviridae_. Sudden-onset acute viral gastroenteritis is most
often caused by noroviruses; indeed, they are more frequent causes of
infective gastroenteritis than _Salmonella_ or _Campylobacter_.
Noroviruses are spread mainly by fecal-oral transmission and to some
extent by the aerosols generated during the vomiting which often
accompanies norovirus infection. These features coupled with a low
infective dose explain the rapid spread of norovirus infection in
closed communities. However, norovirus outbreaks may also be
associated with point-source outbreaks such as contaminated drinking
or recreational water supplies. Food-borne outbreaks are also common
and have involved many types of foods, ice-cubes and shellfish being
among the most common. The epidemiology of norovirus outbreaks is
complex. The 2-year periodicity of outbreaks of norovirus infection
described in the above report is not a regular feature. Human
noroviruses can be grouped into 2 genogroups (GI and GII) and at
least 14 GI and 17 GII genotypes. Human noroviruses cannot be
propagated in cell-culture systems which complicates analysis.
However, expression of recombinant VP1 in insect cells results in the
formation of virus-like particles (VLPs). An antibody ELISA using
polyclonal antisera raised against these VLPs has been used to
determine cross-reactivity. Considerable antigenic diversity was
detected. Antisera reacted strongly with homologous VLPs; however, a
number of novel cross-reactivities among different genotypes was
noted. For example, GI/11 antiserum showed a broad-range
cross-reactivity, detecting 2 GI and 10 GII genotypes. Likewise,
GII/1, GII/10 and GII/12 antisera showed a broad-range
cross-reactivity, detecting several other distinct GII genotypes. For
further details see: Genetic and antigenic diversity among
noroviruses. Hansman GS, et al; J Gen Virol. 2006 Apr;87 (Pt
4):909-19). - Mod.CP]