Published Date: 2002-01-26 23:50:00
Subject: PRO> Norwalk-like virus, hospital outbreak - UK (Scotland) (04)
Archive Number: 20020126.3409
NORWALK-LIKE VIRUS, HOSPITAL OUTBREAK - UK (SCOTLAND) (04)
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See Also
Norwalk-like virus, hosp. outbreak - UK (Scot.) (03) 20020123.3365Norwalk-like virus, hospital outbreak - UK (Scot.) (02) 20020120.3333
Norwalk-like virus, hospital outbreak - UK (Scotland) 20020119.3323
Norwalk-like virus, outbreaks - UK 20020122.3353
Norwalk-like virus, outbreaks - UK (02) 20020123.3367
[1
Date: Thu 24 Jan 2002
From: Kellogg Schwab < 20020123.3365" contained the following statement:
"Medical experts have stressed that the viral outbreak is not related
to hygiene.The infection is an airborne illness, which is highly
contagious."
I have a difficult time believing that these outbreaks are not related
to hygiene. There are very few cases of "Norwalk-like viruses" having
airborne transmission. And those few reports have not been linked to
large numbers of individuals. Almost all of the outbreaks have
occurred from contaminated food, water, or fomites, with ill food
handlers causing many of the outbreaks.
--
Kellogg J. Schwab Ph.D.
Assistant Professor
Johns Hopkins Bloomberg School of Public Health
Department of Environmental Health Sciences
Division of Environmental Health Engineering
615 N. Wolfe St. Room W6001A
Baltimore, MD 21205-2103
<kschwab@jhsph.edu>
******
[2
Date: Thu,24 Jan 2002
From: John P. Maher <jmaher@chesco.org>
Our experience with Norwalk-like illness episodes has been primarily
linked to (most likely) contaminated water, and especially ice. In
addition, Chin's "Control of Communicable Disease Manual (17th Ed.,
2000)", indicates that outbreaks in the USA are usually associated
with consumption of raw shellfish and that "transmission is probably
by the fecal-oral route, although contact or airborne transmission
from fomites has been suggested to explain the rapid spread in
hospital settings. Several recent outbreaks have strongly suggested
primary community foodborne, waterborne and shellfish transmission,
with secondary transmission to family members."
I'd like to know if that information is out of date or subject to
revision as a result of newer knowledge.
--
Maher, John P.
<jmaher@chesco.org>
[These comments were received after the thread was closed, but they
deserve a response. The Norwalk-like virus outbreaks in individual
hospitals and schools could be accounted for by spread from a
contaminated food source or water supply. However, it is difficult to
account for the nationwide prevalence of Norwalk-like virus infection
in the UK at the present time on this basis alone. The following 2
publications originating in recent years from the CDC, Atlanta,
perhaps shed some light on this phenomenon.
In a paper entitled "Cold weather seasonality of gastroenteritis
associated with Norwalk-like vuses", Mount et al. came to the
following conclusions:
"Norwalk-like viruses (NLVs) are the most common cause of acute
non-bacterial gastroenteritis in adults, but little is known about
their seasonality. The lack of specific diagnostic tools impeded study
of these viruses in the past, and surveys using electron microscopy
often grouped NLVs with other unrelated viruses. A search of the
scientific literature found 8 surveys of gastroenteritis, which were
conducted for at least one year, that specifically identified NLVs.
Unpublished data from laboratories of 4 NLV researchers were also
used. These surveys, which were conducted in 8 countries, reported
sporadic cases and outbreaks of NLV-associated gastroenteritis among
all age groups. The monthly occurrence of these cases and outbreaks
was plotted, and while transmission occurred year-round in most
surveys, a cold weather peak was demonstrated in 11 of the 12 studies.
This key epidemiologic feature of the viruses has important
implications concerning their mode of transmission and for
understanding the etiology of acute gastroenteritis in adults." ( J
Infect Dis 2000 May;181 Suppl 2:S284-7).
These data imply that there are other modes of transmission in
addition to local person-to-person transmission from a common source.
In a paper entitled " Identification of a distinct common strain of
Norwalk-like viruses having a global distribution", Noel et al. stated
the following:
"Norwalk-like viruses (NLVs) are the most common cause of outbreaks of
non-bacterial gastroenteritis. During molecular surveillance of NLV
strains from 152 outbreaks of gastroenteritis that occurred in the US
between August 1993 and July 1997, we identified an NLV strain that
predominated during the 1995-1996 season. The "95/96-US" strain caused
60 outbreaks in geographically distant locations within the US and was
identified, by sequence comparisons, in an additional 7 countries on 5
continents during the same period. This is the first demonstration
linking a single NLV strain globally and suggests that the circulation
of these strains might involve patterns of transmission not previously
considered. The diagnostic techniques are now available to establish a
global network for surveillance of NLV strains that would highlight
the importance of NLVs worldwide and allow molecular identification of
common strains having a global distribution so as to consider
interventions for their control." ( J Infect Dis 2000 May;181 Suppl
2:S284-7).
These papers indicate that there are other modes of transmission of
these viruses in addition to those described for specific outbreaks of
limited extent in Norwalk and at other sites in the USA. The
Norwalk-like viruses are a heterogeneous group, and there may be
distinct predominant modes of transmission. Perhaps "Winter vomiting"
should be regarded as an emergent disease. - Mod.CP
...............................................cp/pg/jw
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