NORWALK VIRUS-ASSOCIATED GASTROENTERITIS TRACED TO ICE CONSUMPTION ABOARD A CRUISE SHIP IN HAWAII - COMPARISON AND APPLICATION OF MOLECULARMETHOD-BASED ASSAYS

Investigation of an outbreak of acute nonbacterial gastroenteritis on a cruise ship provided an opportunity to assess new molecular method-b ased diagnostic methods for Norwalk virus (NV) and the antibody respon se to NV infection. The outbreak began within 36 h of embarkation and affected 30% of 672 passengers and crew. No single meal, seating, or f ood item was implicated in the transmission of NV, but a passenger's r isk of illness was associated with the amount of ice (but not water) c onsumed (chi-square for trend, P = 0.009). Of 19 fecal specimens exami ned, 7 were found to contain 27-nm NV-like particles by electron micro scopy and 16 were positive by PCR with very sensitive NV-specific prim ers, but only 5 were positive by a new highly specific antigen enzyme immunoassay for NV. Ten of 12 serum specimen pairs demonstrated a four fold or greater rise in antibody titer io recombinant baculovirus-expr essed NV antigen. The amplified PCR band shared only 81% nucleotide se quence homology with the reference NV strain, which may explain the la ck of utility of the fecal specimen enzyme immunoassay. This report, t he first to document the use of these molecular method-based assays fo r investigation of an outbreak, demonstrates the importance of highly sensitive viral diagnostics such as PCR and serodiagnosis for the epid emiologic investigation of NV gastroenteritis.