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Published Date: 2004-09-15 23:50:00
Subject: PRO/EDR> Viral gastroenteritis update 2004 (29)
Archive Number: 20040915.2569

VIRAL GASTROENTERITIS UPDATE 2004 (29)
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In this update:
[1] Gastroenteritis, cruise ship - UK (Scotland) - salmonellosis
implicated: not norovirus
[2] Norovirus, swimming club - USA (Vermont)
[3] Norovirus, hospital - Ireland (Cork)
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[1] Gastroenteritis, cruise ship - UK (Scotland) - salmonellosis
implicated: not norovirus
Date: Thu 9 Sep 2004
From: ProMED-mail <promed@promedmail.org>
Source: Eurosurveillance Weekly, Thu 9 Sep 2004 [edited]
<http://www.eurosurveillance.org/ew/2004/040909.asp#1>

Cruise ship outbreak attributed to salmonellosis: not norovirus infection
-----------------------------------------------
In "Viral gastroenteritis update 2004 (28)," it was suggested that an
outbreak of undiagnosed gastroenteritis on the cruise ship "Mona
Lisa" might have been caused by norovirus infection, since
noroviruses have been responsible for several outbreaks of
gastroenteritis on board cruise ships, particularly in the Caribbean
region and on the West coast of the USA.
A number of the initial cases in the outbreak have been
microbiologically confirmed as salmonellosis. The Scottish Salmonella
Reference Laboratory has confirmed that a number of the isolates are
_Salmonella enteritidis_ phage type 4. A 2nd wave of cases, however,
raises the possibility of a continuing common source of infection, or
secondary spread of _Salmonella_, or, of a concurrent outbreak
involving another pathogen (such as norovirus).
A fuller account of this investigation can be read by accessing the
ProMED-mail post "Salmonellosis, cruise ship - UK (Scotland)
20040913.2546. Any further information on the progress of this
investigation will be posted in the Salmonellosis, cruise ship - UK
(Scotland) thread.
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ProMED-mail
<promed@promedmail.org>
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[2] Norovirus, swimming club - USA (Vermont)
Date: Fri 3 Sep 2004
From: ProMED-mail <promed@promedmail.org>
Source: Morbidity and Mortality Weekly, Fri 3 Sep 2004 [edited]
<http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5334a5.htm>

An outbreak of norovirus gastroenteritis at a swimming club in Vermont
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John Snow's historic investigation of a severe epidemic of cholera
traced the cause of infection to a common water source (1). Today,
150 years later, waterborne diseases remain a public health problem,
and similar investigations are used to identify the source of
infection. On 3 Feb 2004, the Vermont Department of Health (VDH) was
notified of an outbreak of acute gastroenteritis among children,
whose only common exposure was attendance at a swimming club the
previous weekend (31 Jan to 1 Feb 2004). This report summarizes the
results of an investigation conducted by the VDH and the CDC, which
determined the cause of the outbreak to be a combination of stool
contamination, a blocked chlorine feed tube, and multiple lapses of
pool-maintenance procedures. The findings underscore the importance
of correct pool maintenance for rapid identification of water-quality
problems to prevent outbreaks of swimming pool-associated illness.
Pool attendance records were available for review for the period from
Friday evening, 30 Jan 2004, to Monday noon, 2 Feb 2004. During this
time, 7 private groups used the pool, including 3 mother-infant
swimming classes, 2 groups from a local girls' organization, a
birthday party of children aged 5 to 10 years, and a preschool class.
In addition, members of the club used the pool during 2 defined
open-swim sessions. The 7 private groups ranged in size from 4 to 31
persons. The group leader for each event provided a roster of
attendees. An adult in each household was contacted by telephone and
asked to identify family members who attended events at the swimming
club and to question them about recent gastrointestinal illness by
using a standardized questionnaire. Family members who reported
recent gastrointestinal illness were asked to submit stool specimens
for laboratory testing. Respondents also were asked to describe the
appearance of the pool water at the time of their visit. A case was
defined as vomiting or diarrhea (i.e., >3 loose stools within a
24-hour period) that occurred in a person within 72 hours of visiting
the swimming club.
Of the 189 persons for whom information was collected, and who
visited the pool during the outbreak period, median age was 13 years
(range: 5 months to 73 years); 53 (28 percent) reported an illness
consistent with the case definition. Among these 53 persons, onset of
symptoms began a median of 30 hours (range: 8 to 62 hours) after
attending an event at the club and included vomiting (89 percent),
diarrhea (50 percent), nausea (77 percent), stomach cramps (68
percent), chills (58 percent), and a fever of >100.4 F. (>38 C.) (53
percent). The median age of patients was 7 years (range: 5 months to
61 years); 31 (58 percent) were female. 6 persons (5 children and one
adult) sought medical care from their physicians, and one adult was
hospitalized with severe vomiting. Of the 10 stool specimens tested,
5 were positive for norovirus by reverse transcription-polymerase
chain reaction (RT-PCR). 3 strains [i.e. isolates - Mod.CP] were
characterized further and determined to share identical nucleotide
sequences. The highest attack rates were observed among persons who
visited the pool on Saturday [31 Jan 2004] or Sunday [1 Feb 2004]. No
one who attended Friday's event became ill, and by Sunday afternoon,
the attack rates had declined sharply. No obvious source of
contamination was identified: all infants were reported to have worn
swim diapers while in the pool, no vomiting or fecal incidents were
reported, and no persons, when questioned, reported gastrointestinal
illness in the 2 weeks before visiting the pool. Attending an event
at the club on Saturday or Sunday (versus Friday or Monday, relative
risk [RR] = 7.7; 95 percent confidence interval [CI] = 2.0 to 30.0; p
= 0.003) and going into the pool (RR = 6.0; 95 percent CI = 1.6 to
23.0; p = 0.009) increased risk for illness.
Interviews with swimmers and staff indicated that the water was
visibly cloudy throughout Saturday and on Sunday morning, when the
regular maintenance person was not on duty and pool usage was the
highest. No action was taken until Sunday afternoon, when the pool
was hyperchlorinated (i.e., "shocked") twice. Analysis of a water
sample collected on Monday morning demonstrated low free residual
chlorine (0.5 parts per million [ppm]; normal range: 1 to 4 ppm) and
low pH (6.8; ideal range: 7.4 to 7.6), indicating suboptimal
disinfection. A kink in the tube that supplies chlorine to the pool
was subsequently identified and repaired by the pool-maintenance
manager. The pool was hyperchlorinated again Monday night, and the pH
was corrected to optimize chlorine efficacy.
The pool was equipped with an automated chlorine feeder and
filtration system and was monitored and maintained by lifeguards and
a maintenance worker. On Tue 3 Feb 2004, a comprehensive
environmental health systems review of the pool equipment,
maintenance, and operations was conducted. At the time of the review,
although disinfection equipment was working properly, and pool
chlorine, pH, and temperature were consistent with recommended
national standards (2), multiple lapses and inadequacies in pool
management were identified. Of these, most remarkable were a lack of
staff training and response policies and the absence of records of
pool-chemistry monitoring results, or pool maintenance.
(Reported by: L Zanardi Blevins, MD, D Itani, MS, A Burns, C Lohff,
MD, S Schoenfeld, MSPH, W Knight, N Thayer, J Oetjen, PhD, N Pugsley,
Vermont Dept of Health. C Otto, Environmental Health Svcs, National
Center for Environmental Health; M Beach, PhD, Div of Parasitic
Diseases; M-A Widdowson, VetMB, J Bresee, MD, R Glass, MD, S Monroe,
PhD, L Browne, MPH, S Adams, Div of Viral and Rickettsial Diseases,
National Center for Infectious Diseases; M Amundson, DVM, LJ
Podewils, PhD, EIS officers, CDC.)
MMWR Editorial Note:
Whereas classical infectious disease epidemiological methods were
used to identify and characterize this outbreak, and the risk factors
for illness, several failures in the environmental health systems
likely led to the outbreak. 1st, inadequate monitoring of water
quality by the pool staff resulted in critical delays in detecting
the chlorinator-tube malfunction. Secondly, although the pool staff
and patrons noticed cloudy, turbid water in the pool, the maintenance
staff was not notified, which further delayed implementation of
control measures, such as hyperchlorination, for more than 24 hours.
Thirdly, none of the pool staff had formal training in pool
disinfection. Appropriate monitoring, operation, and response
protocols could have prevented this outbreak or reduced the duration
of virus transmission. Only on Monday [2 Feb 2004], when low free
residual chlorine and pH were measured, despite hyperchlorination the
previous day, was the defective chlorinator discovered. Repair of the
defective chlorination system, and the return of the pool water to
recommended disinfection standards, were associated with resolution
of this outbreak. The findings underscore the importance of free
residual chlorine concentration, and proper pH, in the prevention of
illnesses associated with recreational water use.
Although no obvious source of norovirus was determined, the epidemic
curve and laboratory data were consistent with a single contamination
event, such as fecal incontinence, that occurred on either Friday [30
Jan 2004] night or Saturday [31 Jan 2004] morning. Previous outbreaks
of enteric infections associated with recreational water have
occurred with no obvious contamination event (3,4).
Norovirus remains the most common cause of epidemic gastroenteritis
in the United States, causing an estimated 23 million cases each year
(5). Challenges to prevention of norovirus-associated outbreaks
include the low infectious dose, the multiple modes of transmission
(e.g., person-to-person, foodborne, and waterborne), the absence of
long-lasting immunity, and the diversity of strains that do not
confer heterotypic protection. Although waterborne outbreaks of
norovirus gastroenteritis are much less commonly reported than
foodborne outbreaks (6), the recorded incidence of
norovirus-associated waterborne disease is likely an underestimate
because of the lack of simple diagnostic technology. However,
norovirus outbreaks associated with swimming pools rarely are
reported (7).
Pool-care guidelines are available from the National Spa and Pool
Institute (2) and the state of Vermont; however, use of these
guidelines is voluntary. In addition, the CDC provides guidelines on
how to avoid the risk for infectious illness when swimming (8).
Although prevention of norovirus outbreaks is difficult, this
outbreak investigation suggests that staff training, pool-chemistry
monitoring, and maintenance of appropriate disinfectant levels are
important prevention strategies. As with John Snow's Broad Street
cholera outbreak, a series of environmental health failures occurred,
creating conditions that could convey almost any waterborne pathogen.
Findings from this investigation highlight the need for review of
appropriate guidelines and methods to ensure pools are properly
maintained, and, underscore the utility of environmental health
investigations for providing data for development of prevention
guidelines.
References:
(1) Snow J. On the mode of communication of cholera. 2nd ed. In: Snow
on Cholera. (Reprint). New York, New York: The Commonwealth Fund,
1936:11--39.
(2) National Spa and Pool Institute. Standard for Public Swimming
Pools. Alexandria, Virginia: National Spa and Pool Institute, 1991.
(3) Friedman MS, Roels T, Koehler JE, Feldman L, Bibb WF, Blake P.
Escherichia coli 0157:H7 outbreak associated with an improperly
chlorinated swimming pool. Clin Infect Dis 1999;29:298--303.
(4) Hoebe CJ, Vennema H, de Roda Husman AM, van Duynhoven YT.
Norovirus outbreak among primary schoolchildren who had played in a
recreational water fountain. J Infect Dis 2004;189:699--705.
(5) Mead PS, Slutsker L, Dietz V, et al. Food-related illness and
death in the United States. Emerg Infect Dis 1999;5:607--25.
(6) CDC. Norwalk-like viruses: public health consequences and
outbreak management. MMWR 2001;50(No. RR-9).
(7) CDC. Surveillance for waterborne-disease outbreaks---United
States, 1999--2000. In: Surveillance Summaries, November 22, 2002.
MMWR 2002;51(No. SS-8).
(8) CDC. Healthy swimming 2004. Available at
<http://www.cdc.gov/healthyswimming>
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[3] Norovirus, hospital - Ireland (Cork)
Date: Sat 11 Sep 2004
From: Pablo Nart <p.nart@ntlworld.com>
Source: Breaking News Ireland, Sat 11 Sep 2004 [edited]
<http://www.breakingnews.ie/2004/09/11/story166014.html>

Ireland: norovirus infection closes hospital ward in Cork
-----------------------------------------------
[Norovirus Infection] forced the closure of a ward at Cork University
Hospital last night [Fri 10 Sep 2004].
The orthopedic ward was closed to admissions because of the number of
new cases of infection in the previous 24 hours.
The authorities are also appealing to people who have experienced
symptoms of norovirus infection over the previous 72 hours to stay
away from the hospital, as the virus is highly infectious.
--
Pablo Nart
<p.nart@ntlworld.com>

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