Quantitative characterization of the inhibitory effects of salt, humic acid, and heavy metals on the recovery of waterborne norovirus by electropositive filters

The virus adsorption-elution technique (VIRADEL) using electropositively charged filters is used frequently for recovering enteric viruses from water. The filter-absorbed virus is typically eluted, concentrated, and subsequently detected by culture or molecular methods. Human norovirus (HuNoV), one of the most important waterborne pathogens, cannot be cultivated by conventional culture methods and is typically detected using a reverse transcriptase-polymerase chain reaction (RT-PCR) assay. However, it is plausible that various inhibitors could be concentrated simultaneously during the VIRADEL process and affect RT-PCR assays. In this study, we evaluated the effect of typical inhibitors, including humic acid, heavy metals, and salt, on the recovery of norovirus by two different electropositive filters: 1MDS and Nanoceram. Known amounts of HuNoV and murine norovirus were inoculated in 1 L of surface water containing various concentrations of humic acid, heavy metals (cadmium and lead), or NaCl. Our results indicate that the presence of heavy metals or salt significantly reduced the recovery of virus from the electropositive filters. Thus, care should be taken when analyzing waterborne norovirus using electropositive filters in environments with high concentrations of heavy metal inhibitors or salts.