The Darwin outbreak of oyster-associated viral gastroenteritis.

Approximately 60 persons attended a Christmas dinner, at a Darwin hotel, where oysters were served au natural as part of the menu. Twenty-five of the 28 persons who ate oysters developed symptoms of food poisoning--an attack rate of 89%. Of the 60 persons attending the dinner 44 were investigated. The incubation period and duration of illness were about 36 hours. Diarrhoea occurred in 100% of patients, with colic and nausea in 88% and 80% respectively. Half the patients complained of vomiting and headache. The storage temperature at which the oysters were kept was satisfactory and no bacterial pathogens were grown from the oyster and stool specimens. Electron microscopy revealed two distinct parvovirus-like particles in stool specimens, one of which was identified as Norwalk virus. Serological studies by immune electron microscopy showed the development of antibodies to the Norwalk-like particle by seven out of 10 patients. Confirmatory studies by radioimmunoassay showed a significant rise in antibody titre to Norwalk virus in seven patients.