Detection of Norwalk-like virus infection aboard two US navy ships

Two U.S. Navy ships experienced outbreaks of gastroenteritis following port visits to Southeast Asia during August to September 1999. The USS Peleliu (LHA 5) had 162 (6% attack rate) medical visits and the USS Constellation (CV 64) had 425 medical visits (9% attack rate). Navy Environmental and Preventive Medicine Unit No. 5 personnel conducted on-board molecular diagnostic assays to presumptively detect the presence of genogroup I Norwalk-like viruses (NLV) in both outbreaks. NLV RNA were detected in 4 (80%) of 5 Peleliu stool specimens and in 9 (36%) of 25 from the Constellation. Significant antibody titer rises to NLV antigens were measured in 18 (62%) of 29 Peleliu and 69 (68%) of 102 Constellation cases, but only in 1 (4%) of 28 asymptomatic controls. All environmental swipes were negative for NLV. Stools yielded no bacterial or parasitic enteropathogens. No point source was found for either ship. The on-site laboratory investigation can provide important information for outbreak control and prevention while new cases are still presenting.