Disease transmission and passenger behaviors during a high morbidity Norovirus outbreak on a cruise XXXX , January 2009.

@entity1 @entity391 @entity697 @entity2708
BACKGROUND: Norovirus continues to pose a significant burden on cruise ships, causing an average of 27 confirmed outbreaks annually over the past 5 years. In January 2009, the report of a suspected norovirus outbreak among passengers on a cruise @entity2708 prompted an investigation. METHODS: A retrospective cohort study among passengers was conducted on board the @entity2708 . Questionnaires about health care-seeking behaviors, hygiene practices, and possible norovirus exposures were placed in every cabin. Stool samples from several ill passengers were tested for norovirus by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) and confirmed by sequence analysis. RESULTS: Of 1842 passengers, 1532 (83.2%) returned questionnaires, and 236 (15.4% of @entity1 ) met the case definition. Of these, 95 (40%) did not report to the infirmary. Case passengers were significantly more likely to have an ill cabin mate (relative risk [RR] = 3.0; P < .01) and to have witnessed @entity391 during boarding (RR = 2.8; P = .01). Over 90% of all passengers reported increased hand hygiene practices following the outbreak; 38% of ill passengers and 11% of well passengers decreased participation in public activities. Of 14 samples tested, 12 were positive for norovirus by RT-qPCR; 5 of these were confirmed by sequence analysis and typed as GII.4 Minerva. CONCLUSIONS: @entity1 -to- @entity1 transmission, including an incident of @entity391 during boarding, likely contributed to this high morbidity outbreak. Infirmary surveillance detected only 60% of @entity697 ( @entity697 ) cases involved in this outbreak. Adjustments to outbreak reporting thresholds may be needed to account for incomplete @entity697 reporting and to more rapidly implement control measures.
