Development and evaluation of an IgM capture enzyme immunoassay for diagnosis of recent Norwalk virus infection.

A capture enzyme immunoassay specific for Norwalk IgM class antibody was developed. The assay was moderately sensitive, identifying 33/53 (62%) of patients with naturally acquired Norwalk virus infection and 17/18 (94%) of experimentally infected volunteers. The assay was also specific for IgM class antibody and acute Norwalk virus infection and results were generally reproducible. A specific IgM response correlated with seroconversion by total antibody blocking assay and occurred independently of clinical symptoms. Among 81 symptomatic cases composing seven Norwalk outbreaks, specific IgM was absent from acute phase sera collected less than or equal to three days post onset, and was uncommon in sera collected within one week and after five weeks, with an optimal collection time at about two to three weeks. The Norwalk IgM capture immunoassay may be used to augment paired sera assays in the identification of Norwalk-associated outbreaks of acute gastroenteritis.