A comparison of the efficiency of ELISA and selected primer sets to detect Norovirus isolates in southern Ireland over a four-year period (2002-2006): variation in detection rates and evidence for continuing predominance of NoV GII.4 genotype

Norovirus (NoV) gastroenteritis occurs in all age groups and is the most common cause of gastroenteritis in the community. However, detection methods and rates vary widely, and few data are available to compare these, particularly in Ireland. Detection of noroviruses through antigen and molecular-based strategies was carried out on 135 suspected NoV-positive samples, collected over the course of three NoV outbreaks, from 2002 to 2006, in the southern region of Ireland. A commercially available ELISA and a panel of six primer sets were evaluated to determine their suitability for NoV detection in Irish clinical samples. The key findings of this study were the detection of both GGI and GGII noroviruses by ELISA, but the detection of only GGII noroviruses by RT-PCR. In addition to this, a variation in the levels of detection from 9.4 % to 17.3 % was observed for conventional PCR assays, while a detection rate of 46.3 % was observed for the real-time PCR assay. A proportion (17.8 %) of samples were found to be negative by all detection strategies, suggesting the possibility of reporting false positives for these samples or low-copy positives that do not often repeat. Sequencing information from selected samples also revealed nucleotide polymorphisms, compromising efficient primer binding in the case of one primer pairing. Phylogenetic analysis of the partial polymerase gene identified NoV GII.4 as the dominant genotype, in accordance with previous NoV studies in Ireland. Investigating the NoV diversity of the circulating strains and the dynamics of strain replacement is important to better assess the efficacy of future NoV vaccines and to facilitate the early detection of changes in circulating NoV strains.