Detection of Norovirus and Rotavirus Present in Suspended and Dissolved Forms in Drinking Water Sources

We investigated the present forms of genogroup II norovirus and group A rotavirus in surface water used for drinking water production. River water samples (N = 15) collected at a drinking water treatment plant (DWTP) monthly from June 2017 to August 2018 were fractioned by filtration through 10- and 0.45-μm-pore-size membranes, and viruses present in suspended and dissolved forms were quantitatively detected. Norovirus GII was present in > 10-μm- and 0.45-10-μm-suspended and dissolved forms with detection rates of 33%, 60%, and 87%, respectively. Rotavirus A was detected more frequently than norovirus GII in each form (> 10 μm suspended, 73%; 0.45-10 μm suspended, 93%; dissolved, 100%). We also analyzed surface water samples from 21 DWTPs all over Japan in non-epidemic and epidemic seasons of gastroenteritis. Norovirus GII was detected in 48% and 81% of samples with the concentrations of up to 4.1 and 5.3 log₁₀ copies/L in dissolved form in non-epidemic and epidemic seasons, respectively, and GII.4 Sydney 2012 was predominant genotype followed by GII.2. Rotavirus A was detected in 95% and 86% of samples with the maximum concentrations of 5.5 and 6.3 log₁₀ copies/L in dissolved form in respective seasons. Concentration of norovirus GII was similar in 0.45-10-μm suspended and dissolved forms, while there was a significant difference for rotavirus A (P < 0.01, pared t test), indicating that rotavirus A was less associated with suspended solids in the surface water samples compared to norovirus GII. Our observations provide important implications for understanding of viral behavior in environmental waters.