Noroviruses (NoVs) are recognized as the leading cause of epidemic and sporadic acute gastroenteritis. Early detection of NoV is crucial to control the spread of the disease. In this study, we evaluated the diagnostic accuracy, analytical sensitivity, and analytical reactivity of the IDEIA Norovirus assay (an enzyme immunoassay [EIA]) in a prospective and retrospective study design. A total of 557 prospectively collected fecal samples and a panel of 97 archived fecal samples, including 21 different GI and GII genotypes, were tested by conventional reverse transcription-PCR (RT-PCR)/bidirectional sequencing, real-time RT-PCR, and electron microscopy. The sensitivity and specificity of the EIA were 57.6% and 91.9%, respectively. The sensitivity for detecting NoV in fecal samples from outbreaks improved from 44.1% when three samples were tested to 76.9% when five samples per outbreak were tested. The EIA was able to detect strains from 7 GI and 11 GII genotypes. The analytical sensitivity of the EIA was 3.1 x 10(6) and 1.6 x 10(7) virus particles g(-1) of fecal sample for NoV GI and GII strains, respectively. Most GII samples positive by EIA had a threshold cycle (C(T)) of <26.5, and 50% of the GII samples negative by EIA had a C(T) of >25.6, suggesting that, although strains from genotypes GI.8, GII.10, and GII.16 were not detected, the low sensitivity of the EIA is primarily caused by low virus concentration. In conclusion, the current EIA may be of use as a rapid screening test during a norovirus outbreak investigation when multiple fecal samples are available; however, sporadic samples should be tested by molecular methods.