High Genetic Variability of Norovirus Leads to Diagnostic Test Challenges

BACKGROUND It is important to understand the diagnostic accuracy of multiplex panels such as the Luminex xTAG® Gastrointestinal Pathogen Panel (GPP) as they are increasingly employed for routine diagnostics worldwide. Recent evaluations in our laboratory identified lower detection rates of norovirus genogroup II (NoV GII) using GPP compared to our laboratory-developed RT-qPCR, Gastroenteritis Virus Panel (GVP). OBJECTIVES To characterize the cases of discordant NoV GII results between GPP and GVP and determine the sensitivity of the two assays for specific NoV GII genotypes. STUDY DESIGN We genotyped discordant NoV GII strains identified in stool samples or rectal swabs collected prospectively from a cohort of children with acute gastroenteritis between December 2014 and July 2016. The sensitivities of GVP and GPP for NoV GII were compared by analyses of GVP threshold cycle (Ct) and ten-fold serial dilutions of positive samples of various NoV GII genotypes. RESULTS All discordant samples (63/607) were NoV GII positive by GVP but negative by GPP. Twenty-two were successfully genotyped, fourteen of which were NoV GII genotype 2 (GII.2). The median Ct value of concordant positives was lower than that of discordant results (19.8 vs. 33.7; P<0.0001). GVP was 10 and at least 10,000-fold more sensitive than GPP in detecting NoV GII.3 and GII.2, respectively, but has similar sensitivity for NoV GII.4. Discordant GII.2 variant differed genetically from concordant GII.2 variants. CONCLUSIONS GPP has lower sensitivity to detect NoV GII.2 than GVP and its use may lead to undetected cases clinically, and an underestimation of NoV disease burden at the population level.