Published Date: 2002-12-12 23:50:00
Subject: PRO/EDR> Norwalk-like virus, cruise ship - USA (FL) (15)
Archive Number: 20021212.6049
NORWALK-LIKE VIRUS, CRUISE SHIP - USA (FL) (15)
A ProMED-mail post
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International Society for Infectious Diseases
Date: Thu 12 Dec 2002
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Source: Morbidity and Mortality Weekly Report, 51(49): 1112-1115, Fri
13 Dec 2002 [edited]
Outbreaks of Gastroenteritis Associated with Noroviruses on Cruise
Ships - United States, 2002
During the period 1 Jan to 2 Dec 2002, CDC's Vessel Sanitation
Program (VSP), which conducts surveillance for acute gastroenteritis
(AGE) on cruise ships with foreign itineraries sailing into U.S.
ports (1), received reports of 21 outbreaks of AGE on 17 cruise
ships. Of the 21 outbreaks, nine were confirmed by laboratory
analysis of stool specimens from affected persons to be associated
with noroviruses [previously called "Norwalk-like viruses"], 3 were
attributable to bacterial agents, and 9 were of unknown etiology; 7
outbreaks were reported in 2001, and of these, 4 were confirmed to be
associated with norovirus (CDC, unpublished data, 2002). This report
describes 5 of the norovirus outbreaks that occurred during the
period 1 Jul to 2 Dec 2002, on cruise ships.
Cruise Ship A. On 18 Jul 2002, cruise ship A, owned by cruise line A,
embarked 1318 passengers and 564 crew members for a 7-day cruise from
Vancouver to Alaska. On 19 Jul 2002, 5 passengers reported to the
ship's infirmary with symptoms of AGE. By 25 Jul 2002, a total of 167
(13 percent) passengers and nine (2 percent) crew members had
reported illness. Among the 176 patients, the predominant symptoms
were vomiting (76 percent) and diarrhea (73 percent).
5 of 10 stool specimens from ill passengers were positive for
norovirus by reverse transcriptase polymerase chain reaction
(RT-PCR). On 25 Jul 2002, when passengers disembarked, the ship was
disinfected in accordance with CDC recommendations, and the same day,
a new group of passengers embarked for another 7-day cruise. During
the cruise, 189 (14 percent) of 1336 passengers and 30 (5.3 percent)
of 571 crew members had AGE with diarrhea (91 percent) and vomiting
(85 percent). An environmental health inspection conducted by CDC
revealed no sanitary deficiencies. Cruise line A cancelled a
subsequent cruise and voluntarily took the ship out of service for 1
week for aggressive cleaning and sanitizing. No outbreaks were
reported on subsequent cruises.
Cruise Ship B. On 1 Oct 2002, cruise ship B, also owned by cruise
line A, embarked 1281 passengers and 598 crew members for a 21-day
cruise from Washington to Florida. By 16 Oct 2002, a total of 101 (8
percent) passengers and 14 (2 percent) crew members reported to the
infirmary with AGE symptoms. On 118 Oct 2002, CDC investigators
boarded the ship to conduct an epidemiologic and environmental
investigation. Of 972 surveyed passengers, 399 (41 percent) met the
case definition for AGE. Investigators found no association between
illness and water, specific meals served on the ship, or with
offshore excursions. Stool specimens from 12 of 13 patients tested
positive for norovirus.
Characterization of the strain by sequence analysis of RT-PCR
products matched those from cruise ship A. Despite implementation of
control measures that included disinfection of the vessel and
quarantine of ill passengers and crew members, a total of 264
passengers and 41 crew members reported illness on three subsequent
10-day cruises. Cruise line A voluntarily withdrew cruise ship B from
service for 10 days for aggressive cleaning and sanitizing. No
outbreaks were reported on subsequent voyages.
Cruise Ship C. On 28 Sep 2002, cruise ship C, owned by cruise line B,
embarked 1984 passengers and 941 crew members for a 7-day round-trip
cruise from Florida to the Caribbean. Several passengers had AGE
within 24 hours of embarkation, and by 1 Oct 2002, a total of 70 (4
percent) passengers and two (0.2 percent) crew members reported
illness. On 3 Oct 2002, CDC investigators boarded the ship to conduct
an epidemiologic and environmental investigation.
Questionnaires completed by 1879 (95 percent) passengers and 860 (91
percent) crew members identified 356 (19 percent) passengers and 13
(1.5 percent) crew members who met the AGE case definition. The
epidemiologic investigation suggested a point source of infection,
followed by cases associated with person-to-person transmission. The
investigation identified an association between illness among
passengers and lunch served at embarkation (odds ratio=2.4; 95
percent confidence interval=1.1 to 5.2; p value=0.02). 4 of 11 stool
specimens from patients were positive for norovirus by RT-PCR.
Characterization of the strain by sequence analysis of RT-PCR
products matched those from an outbreak on the same ship that
occurred 3 weeks previously but was not identical to the outbreak
strain on cruise ships A and B. CDC recommended reinforcing
sanitation practices and excluding ill food-handlers from the work
place. Cruise ship C continued service, and no new cases were
reported on subsequent cruises.
Cruise Ship D. On 25 Oct 2002, cruise ship D, owned by cruise line C,
embarked 2882 passengers and 944 crew members in Spain for a 14-day
cruise to Florida. On 28 Oct 2002, a total of 70 (2.5 percent)
passengers reported to the infirmary with AGE; the number of ill
passengers declined rapidly during the following days. By 2 Nob 2002,
a total of 106 (5 percent) passengers and 25 (3 percent) crew members
had reported illness. Stool specimens from 4 of 6 patients tested
positive for norovirus by RT-PCR. Characterization of the strain by
sequence analysis of RT-PCR products identified a strain distinct
from the other cruise-ship outbreaks. With passengers aboard, control
measures included quarantine of ill crew members until symptom-free
for 72 hours, disinfection of the ship, and reinforcement of
sanitation practices. No new outbreaks were reported on subsequent
Cruise Ship E. On 16 Nov 2002, cruise ship E, owned by cruise line D,
embarked 2318 passengers and 988 crew members for a 7-day cruise from
Florida to the Caribbean. By 20 Nov 2002, a total of 28 (1 percent)
passengers and 7 (1 percent) crew members had reported to the ship's
infirmary with AGE. By disembarkation on 23 Nov 2002, a total of 260
(12 percent) passengers and 17 (2 percent) crew members had reported
illness. On 23 Nov 2002, CDC investigators boarded the ship and
collected questionnaires that had been distributed to all passengers
before disembarkation. A total of 1280 (55 percent) passengers
returned a questionnaire; of these, 492 (21 percent) met the case
definition for AGE. 7 of 12 specimens from patients were positive for
norovirus by RT-PCR. Characterization of the strain by sequence
analysis of RT-PCR products identified a perfect match with those
products from the outbreaks on cruise ships A and B. Despite
implementation of disinfection and sanitation measures, the outbreak
continued on the subsequent cruise. On 30 nov 2002, cruise line D
removed the ship from service for 1 week for aggressive cleaning and
Reported by: EH Cramer, MD, D Forney, Vessel Sanitation Program; AL
Dannenberg, MD, Div of Emergency and Environmental Health Svcs,
National Center for Environmental Health; MA Widdowson, VetMB, JS
Bresee, MD, Monroe, PhD, RS Beard, H White, MS, S Bulens, MPH, Div of
Viral and Rickettsial Diseases; E Mintz, MD, C Stover, MPH, Div of
Bacterial Diseases, National Center of Infectious Diseases; E
Isakbaeva, MD, J Mullins, DVM, J Wright, DVM, V Hsu, MD, W Chege, MD,
J Varma, MD, EIS officers, CDC.
MMWR Editorial Note:
Cruise-ship outbreaks demonstrate how easily noroviruses can be
transmitted from person to person in a closed environment, resulting
in large outbreaks (2, 3, 4). The continuation of these outbreaks on
consecutive cruises with new passengers and the resurgence of
outbreaks caused by the same virus strains during previous cruises on
the same ship, or even on different ships of the same company,
suggests that environmental contamination and infected crew members
can serve as reservoirs of infection for passengers.
The increase in reported norovirus outbreaks on cruise ships in 2002
might reflect an actual increase in norovirus outbreaks, or it might
be attributable to improved surveillance with an electronic reporting
format implemented on 1 Jan 2001, and increased application of
sensitive molecular assays. The surveillance system captures cases of
illness reported to the ship's infirmary or to designated staff on
board the ship. Other cases of AGE among passengers and crew members
are not reported. In 2002, CDC has confirmed 26 land-based outbreaks
of AGE attributable to norovirus; 3 were caused by strains closely
related to the strain detected from cruise ships A, B, and E.
Although several land-based outbreaks are linked to norovirus strains
with unique sequence types, strains with identical sequence types are
identified commonly in outbreaks with no obvious epidemiologic link.
Further genetic characterization of common outbreak strains
associated with epidemiologic data might help establish possible
links among these outbreaks.
Noroviruses (i.e., Norwalk-like viruses or NLV) are members of the
family Caliciviridae and are well-recognized etiologic agents of
non-bacterial AGE (5). Noroviruses cause approximately 23 million
cases of AGE each year and are the leading cause of outbreaks of
gastroenteritis (5,6). Illness caused by norovirus infection lasts 12
to 60 hours and is characterized by sudden onset of nausea, vomiting,
and watery diarrhea (7); the incubation period is 12 to 48 hours. The
virus is transmitted by hands contaminated through the fecal-oral
route, directly from person to person, through contaminated food or
water, or by contact with contaminated surfaces or fomites (8).
Aerosolized vomitus also has been implicated as a transmission mode
(9). Because of high infectivity and persistence in the environment,
transmission of noroviruses is difficult to control through routine
sanitary measures (3,4,9).
Although norovirus causes a self-limited AGE, elderly passengers,
children, and those with severe underlying medical conditions might
be at increased risk for complications because of volume depletion
and electrolyte disturbances. Hospitalization of adults with
norovirus who are otherwise healthy is rare. Neither specific
antiviral treatment nor a vaccine has been developed for noroviruses.
In addition to emphasizing basic food and water sanitation measures,
control efforts should include thorough and prompt disinfection of
ships during cruises, and isolation of ill crew members and, if
possible, passengers for 72 hours after clinical recovery. Suitable
disinfectants include freshly prepared chlorine solutions at
concentrations of >1000 ppm, phenol-based compounds, and accelerated
hydrogen peroxide products (10). Cruise ships also should promote
frequent, rigorous hand washing with soap and water by passengers and
Rapid implementation of control measures at the first sign of a
suspected AGE outbreak is critical in preventing additional cases.
When routine disinfection measures are unsuccessful at interrupting
the spread of virus during an outbreak, more extensive disinfection
and a period of time without passengers aboard a ship might
facilitate elimination of the virus.
CDC encourages local and state health departments to test for
noroviruses when investigating outbreaks of suspected viral AGE. For
assistance in testing for noroviruses and for strain
characterization, local and state health departments should contact
CDC's Viral Gastroenteritis Section,telephone 404-639-3577 or by
(1)CDC. Vessel Sanitation Program Operations Manual 2000. Atlanta,
Georgia: U.S. Department of Health and Human Services, CDC, 2000.
(2)Addiss DG, Yashuk JC, Clapp DE, Blake PA. Outbreaks of diarrheal
illness on passenger cruise ships, 1975--85. Epidemiol Infect
(3)Gunn AG, Terranova WA, Greenberg HB, et al. Norwalk virus
gastroenteritis aboard a cruise ship: an outbreak on five consecutive
cruises. Am J Epidemiol 1980;112:820--7.
(4) CDC. Gastroenteritis outbreaks on two Caribbean cruise ships.
(5) Fankhauser RL, Monroe SS, Noel JS, et al. Epidemiologic and
molecular trends of "Norwalk-like viruses" associated with outbreaks
of gastroenteritis in the United States. J Infect Dis 2002;186:1--7.
(6) Mead PS, Slutsker L, Dietz V, et al. Food-related illness and
death in the United States. Emerg Infect Dis 1999;5:607--25.
(7) Kaplan JE, Gary GW, Baron RC, et al. Epidemiology of Norwalk
gastroenteritis and the role of Norwalk virus in outbreaks of acute,
non-bacterial gastroenteritis. Ann Int Med 1982;96:756--61.
(8) CDC. "Norwalk-like viruses": public health consequences and
outbreak management. MMWR 2001;50(No. RR-9).
(9) Marks PJ, Vipond IB, Carlisle D, Deakin D, Fey RE, Caul ED.
Evidence for airborne transmission of Norwalk-like virus (NLV) in a
hotel restraurant. Epidemiol Infect 2000;124:481--7.
(10) Gulati BR, Allwood PB, Hedberg CW, Goyal SM. Efficacy of
commonly used disinfectants for the inactivation of calicivirus on
strawberry, lettuce, and a food-contact surface. J Food Prot
[These data confirm unequivocally that noroviruses have been
responsible for the many of the outbreaks of viral gastroenteritis
affecting passengers and crew of cruise ships during the past year.
Inadequate disinfection has been a factor is some but not all
recurrent outbreaks, and more than a single strain of norovirus has
been involved. - Mod.CP]