Nucleotide Correlations Between Rotavirus C Isolates in Clinical Samples from Outbreaks and in Sewage Samples

Rotavirus C (RVC) is detected in both sporadic cases and outbreaks of gastroenteritis worldwide. However, the epidemic dynamics of RVC in populations remain poorly understood because the detection rate is low. In this study, raw sewage samples were collected from a wastewater treatment plant in Yokohama, Japan, over 5 years, in 12-month period from September to August, to identify the RVC strains in these samples and compare them with the RVC strains circulating in the population. RVC strains were detected in 15 of the 118 raw sewage samples collected between 2007 and 2012. The highest number of positive samples detected per period (seven) was in 2008-2009. A fragment (225 nucleotides) of the VP7 gene of RVC from 14 sewage samples was sequenced. The nucleotide sequences of 11 strains were completely consistent with those of clinical strains identified in Yokohama. A phylogenetic analysis showed that 13 strains from the sewage samples clustered with several Yokohama outbreak strains and were closely related to the clinical strains (except sewage-derived strain Y11-SW0805-C). Our study demonstrates a correlation between clinical and sewage strains of RVC based on a genetic analysis, and shows that monitoring environmental samples is an effective way to study the strains circulating in a population, including in asymptomatic or mildly symptomatic patients, even when these infections are not detected in clinical samples. This is the first report of the surveillance of RVC in sewage samples in Yokohama, Japan, for molecular epidemiological analysis.