Norovirus outbreak on cruise ship highlights need for increased prevention measures

Wikswo M. Clin Infect Dis. 2011; doi:10.1093/cid/cir144.

Person-to-person transmission of norovirus infection was the likely cause of a high-morbidity outbreak on a cruise ship during 2009. CDC researchers, therefore, recommend for passengers to avoid travelling on cruise ships when ill, and for those who become ill once on board to report to the ship’s medical center as soon as possible to prevent an outbreak from occurring.

“Incentives to encourage ill passengers to report their illness to ship personnel may help to prevent the introduction of norovirus onto cruise ships and enable more-timely interventions, particularly if aggressive sanitation measures are adopted at the first signs of a possible acute gastroenteritis outbreak,” the researchers wrote.

Norovirus infection has caused, on average, 27 outbreaks on cruise ships every year during the past 5 years, according to background information in the study published in Clinical Infectious Diseases. After a suspected norovirus outbreak on a cruise ship during January 2009, Mary E. Wikswo, MD, MPH, in the division of viral diseases at the National Center for Immunization and Respiratory Diseases at the CDC, and colleagues conducted a retrospective cohort study and examined data on health care-seeking behaviors, hygiene practices, and possible norovirus exposures via questionnaires administered after the outbreak began.

Of the 1,532 returned questionnaires, 236 met case definition of acute gastroenteritis. Cases were more likely to have witnessed vomiting during boarding (RR=2.8; P=.01) and were more likely to have an infected roommate (RR=3.0; P<.01). Moreover, 40% of cases reported they did not seek medical care at the cruise ship infirmary.

An increase in hand hygiene practices was reported in more than 90% of passengers after the outbreak. In addition, 11% of well passengers and 38% of infected cases reported decreased participation in public activities. Twelve of 14 case stool samples tested positive for norovirus; five were confirmed as GII.4 Minerva.

The researchers determined that norovirus was likely introduced when passengers with already active illness boarded the ship and was dispersed with a public vomiting incident. The low attack rate reported in cruise ship personnel may be due to their separate sleeping and dining areas, and different entrance and exit areas on the ship, according to the researchers.

“Cruise line personnel should discourage ill passengers from boarding their ships,” Wikswo said in a press release. “Once on board, passengers and crew who become ill should report to the ship’s medical center as soon as possible. These quick actions are crucial in preventing the introduction and spread of norovirus on cruise ships and allow ship personnel to take immediate steps to prevent the spread of illness.”

Disclosure: The researchers report no relevant financial disclosures.

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