Diagnosis of Norovirus outbreaks by commercial ELISA or RT-PCR.

The IDEIA Norwalk-like virus (Dakocytomation Ltd., Ely, United Kingdom) and the Ridascreen Norwalk-like virus enzyme immunoassay (R-Biopharm AG, Darmstadt, Germany), were evaluated for the diagnosis of outbreaks of acute gastroenteritis. A panel of 158 fecal samples from 23 outbreaks, including confirmed rotavirus and astrovirus outbreaks, was used to determine the sensitivity and specificity of both ELISA kits relative to an RT-PCR protocol that was followed by Southern blot hybridization. Another panel consisted of 6 different genogroup I strains, 12 genogroup II strains and 1 genogroup IV strain and was used to determine the scope of the tests. Compared to the RT-PCR, sensitivities of 38% and 36% and specificities of 96% and 88% were found for the Dako kit and the Ridascreen kit, respectively. Two genogroup I strains, and one genogroup II strain were not detected by the Dako kit, while five genogroup I and five genogroup II strains were not detected by the Ridascreen kit. The sensitivity of both ELISA kits, and the scope of the Ridascreen are considered disappointing. However, the ELISA kits can be useful for a preliminary screening, provided that ELISA negative outbreaks will be re-tested by RT-PCR methods.