Human enteric viruses in oysters causing a large outbreak of human food borne infection in 1996/97

During the New Year of 1996/97, more than 350 persons in Denmark became ill from consumption of imported oysters. The main symptoms were vomiting, dia rrhea, abdominal pain, and fever: commencing 12 to 48 hrs after consumption . In addition, a number of the diseased persons reported secondary symptoms , such as aching joints, skin numbness, and visual disturbances, commencing 24 h after onset of the primary symptoms. In,general, recovery from both t he primary and, in particular, the secondary symptoms was slow. Only 3/24 ( 12%) of the analyzed samples of infected oysters showed an E. coli level ab ove the allowed regulatory limit. A small amount of domoic acid was found i n 4/9 (44%) of analyzed samples. Small round-structured virus (SRSV) and en terovirus were identified from both oyster and fecal samples, using RT-PCR. Enterovirus isolated from individual fecal samples showed sequence identit y of 3 PCR amplicons, suggesting a common source of infection. The identity of the enterovirus is still under investigation. The characteristic clinic al symptoms and RT-PCR results implicate SRSVs as the cause of the primary symptoms. However, the cause of the secondary symptoms is currently unclear . Although the detection of enterovirus in both fecal samples and oysters i s significant, the incubation period prior to onset of secondary symptoms w as not typical of an enterovirus infection. The significance of the domoic acid in relation to the outbreak is unclear.