Evaluation of a new commercial assay for the detection of norovirus in stool samples

Noroviruses are important human pathogens causing acute gastroenteritis; they can hardly be propagated in any cell culture system and are often difficult to visualize by using electron microscopy (ME). These aspects, as well as the need of an accurate diagnosis justify the development of a number of rapid diagnostic methods aimed at improving the identification of noroviruses and based on the research of viral genomic sequences or, alternatively, of norovirus specific proteins. In this study 60 stool samples were analyzed by traditional techniques, such as cell culture (MT), and by rapid methods like ME and nested reverse transcriptase-polimerase chain reaction (nRT-PCR).A third rapid test, the immunochromatographic assay RIDA ®QUICK Norovirus (R-Biopharm) for the research of norovirus proteins (belonging to genogroups I and II), was used retrospectively on the same samples stored at -80°C. The results obtained by using nRT-PCR (i.e. the most sensitive method) and the immunochromatographic assay were compared, showing that 39 samples were positive and 21 negative in nRT-PCR, while only 28 (71.8%) were positive with the immunochromatographic assay; among the negative samples, one resulted positive with RIDA ®QUICK Norovirus. The latter test proved to be appreciably sensitive, even if nRT-PCR still remains the gold standard method for the laboratory diagnosis of norovirus. Nevertheless, the easy-to-use and cheaper immunochromatographic assay can be usefully applied as a screening test.