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Cramer, EH; Blaton, CJ; Blanton, LH; Vaughan, GH; Bopp, CA; Forney, DL.  "Epidemiology of Gastroenteritis on Cruise Ships, 2001 - 2004," American Journal of Preventive Medicine, March 2006, 30 (3): 252-257.

The incidence of diarrheal disease among cruise ship passengers declined from 29.2 cases per 100,000 passenger days in 1990 to 16.3 per 100,000 passenger days in 2000. In 2002, the Vessel Sanitation Program of the Centers for Disease Control and Prevention reported 29 outbreaks (3% or more passengers ill) of acute gastroenteritis on cruise ships, an increase from 3 the previous year. This analysis of gastroenteritis on cruise ships, conducted in 2005, details the increase in outbreak incidence rates during 2001 through 2004. Using Gastrointestinal Illness Surveillance System data, investigators evaluated incidence rates of gastroenteritis on cruise ships calling on U.S. ports, carrying 13 or more passengers, by cruise length and reporting region during the study period. The investigators also evaluated the association between inspection scores, and gastroenteritis incidence and the frequency of outbreaks in 2001 through 2004. During the study period, the background and outbreak-associated incidence rates of passengers with acute gastroenteritis per cruise were 25.6 and 85, respectively. Acute gastroenteritis outbreaks per 1000 cruises increased overall from 0.65 in 2001 to 5.46 in 2004; outbreaks increased from 2 in 2001 to a median of 15 per year in 2002–2004. Median ship inspection scores remained relatively constant during the study period (median 95 on a 100-point scale), and were not significantly associated with either gastroenteritis incidence rates (risk ratio, 1.00; 95% confidence interval, 0.98–1.02) or outbreak frequency (Spearman’s coefficient, 0.01, p=0.84).  Despite good performance on environment health sanitation inspections by cruise ships, the expectation of passenger cases of gastroenteritis on an average 7-day cruise increased from two cases during 1990–2000 to three cases during the study period. This increase, likely attributable to noroviruses, highlights the inability of environmental programs to fully predict and prevent risk factors common to person-to-person and fomite spread of disease.

Cramer EH, Gu DX, Durbin RE.  "Diarrheal disease on cruise ships: 1990-2000: the impact of environmental health programs,"
American Journal of Preventative Medicine, Apr 2003, 24(3):227-33.

In 1975, the then-Center for Disease Control (CDC) established the Vessel Sanitation Program (VSP) to minimize the risk for diarrheal disease among passengers and crew aboard ships by assisting the cruise ship industry in developing and implementing comprehensive environmental health programs. To evaluate the relationship between cruise ship sanitation scores and diarrheal disease incidence and outbreaks among cruise ship passengers. Retrospective cohort study of ship inspection and diarrheal disease data from 1990 through 2000 from the National Center for Environmental Health, CDC database, for cruise ships entering the United States. Yearly trends in number of ships inspected, number of inspections conducted, inspection scores, and risks of failing inspections; rates of diarrheal disease among passengers, by inspection year, cruise duration, incidence of outbreaks, and passing- or failing-score status of the associated ship. From 1990 through 2000, inspection scores gradually increased from a median of 89 in 1990 to 93 in 2000 (p<0.001), with an associated statistically significant 21% increase in likelihood of passing. The total baseline level of diarrhea among passengers was 2.0 cases per cruise (13243/6485), or 23.6 cases per 100,000 passenger-days (13243/56129096). The latter rate declined significantly from 29.2 in 1990 to 16.3 in 2000 (p<0.0001). Diarrheal disease incidence rates among passengers sailing on ships that passed environmental inspections were significantly lower than rates among passengers sailing on ships that failed inspections (21.7 vs 30.1; RR = 1.39; 95% CI: 1.31-1.47). Diarrheal disease outbreak-related illnesses decreased from 4.2 to 3.5 per 100000 passenger-days from 1990-1995 to 1996-2000. Environmental sanitation inspections conducted among ships sailing into the United States appear to continue to decrease diarrheal disease rates and outbreaks among passengers.

Cramer, E. H.;  Forney, D.;  Dannenberg, A. L.;  Widdowson, M. A.;  Bresee, J. S.;  Monroe, S.;  Beard, R. S.;  White, H.;  Bulens, S.;  Mintz, E.;  Stover, C.;  Isakbaeva, E.;  Mullins, J.;  Wright, J.;  Hsu, V.;  Chege, W. and Varma, J.  "Outbreaks of gastroenteritis associated with noroviruses on cruise ships - United States, 2002," Morbidity and Mortality Weekly Report, 2002, 51:49, 1112-1115

This report describes 5 norovirus-associated gastroenteritis outbreaks that occurred during 1 July-2 December 2002 on cruise ships with foreign itineraries sailing into ports in the USA. The cruise ship outbreaks demonstrate how easily norovirus can be transmitted from person to person in a closed environment.