Epidemiology of Norwalk virus during an outbreak of acute gastroenteritis aboard a US aircraft carrier.

A large outbreak of acute gastroenteritis occurred over a 5-week period aboard an aircraft carrier. The estimated cumulative attack rate was 13% among the 4,500-man crew. Eight percent of the crew sought medical attention, nearly all of whom missed 1 day or more of work. The risk of developing illness was 2 to 3 times greater for individuals living in more crowded sleeping quarters (> 50 persons per compartment). Occurrence of gastroenteritis was associated with a fourfold or more rise in Norwalk virus antibody levels, as measured by an enzyme-linked immunoassay utilizing a baculovirus expressed recombinant antigen. In addition, 27 nm Norwalk virus-like particles were visualized in two of six stools examined by immune electron microscopy. The presence of a low (< 1:50) or a high (> or = 1:6,400) pre-illness antibody level was associated with a lower incidence of illness. This investigation indicates that Norwalk virus can adversely impact operations of a military vessel and that crowding is a major risk factor in transmission.