Gastrointestinal Virus Outbreaks Strike European Cruise Ships

Abstract

European scientists studying food-borne viruses have recorded 45 outbreaks of norovirus on cruise ships in European waters. A report in the August 11, 2006 issue of Science notes that this is “a sharp increase from previous years,” adding that a similar spike in case numbers occurred on US ships a few years ago. In some cases, >40% of all passengers on a cruise ship have become ill. Moreover, several ships have experienced outbreaks on ≥3 subsequent trips, despite sterilization attempts between cruises. Although thorough disinfection after a cruise can eliminate the virus, crewmembers can carry it to the next cruise, as can new passengers. According to an epidemiologist with the European Centre for Disease Prevention and Control, the outbreaks are most likely the result of an increased level of norovirus activity in the general population following the emergence of new strains (Figure 1). Some virologists at the National Institute of Public Health and the Environment (RIVM) in Bilthoven, the Netherlands, support this likelihood. They note the recent appearance of 2 new strains of norovirus within the same genogroup in the past year. In 2002, hospitals across Europe reported an increased frequency of cases attributable to noroviruses. Many researchers placed the blame for these cases on a new strain of the virus within genogroup 114, the group of noroviruses that assumed predominance in 2002. According to the Science report, RIVM virologist Dr Harry Venemma said he suspects that noroviruses may evade host immune systems through frequent genetic changes, thereby triggering “fresh outbreaks along the way.” But the absence of an animal model and the inability of culturing noroviruses in the laboratory would make that difficult to investigate. In that regard, Centers for Disease Control and Prevention officials point out that recent advances in finding a cell culture system for noroviruses may allow for assessing the efficacy of various disinfectants. However, only by full epidemiologic investigation of viral gastroenteritis outbreaks and by application of molecular tests will transmission routes be determined, differences in epidemiology between strains be detected, and targeted control measures implemented. “Norovirus infections are common and likely to become more so. Effective prevention strategies must now be designed and implemented.” For further details, see Science 2006;313:747.