Environmental surveillance and molecular characterization of human enteric viruses in tropical urban wastewaters

Aims: To study the prevalence and genotypes of waterborne pathogenic viruses in urban wastewaters in the tropical region. Methods and Results: Viruses in wastewaters collected at three water reclamation plants in Singapore were studied by molecular methods. Over a 6-month sampling period, adenoviruses, astroviruses and both norovirus genogroups I (GI) and II (GII) were detected in 100% of the sewage and secondary effluent. Enteroviruses and hepatitis A viruses (HAV) were found in 94 and 78% of sewage, and 89 and 28% of secondary effluent, respectively. By using quantitative real-time PCR, estimated concentrations of astrovirus in the sewage were 1-2 orders of magnitude higher than those for adenovirus, noroviruses GI and GII. Genotyping of environmental isolates revealed multiple genotypes of GI and GII noroviruses. Coxsackieviruses A, astrovirus type 1 and adenovirus type 41 were prevalent. Norovirus GII/4 and coxsackievirus A24 isolates in wastewaters were closely related to respective outbreak strains isolated previously in Singapore. Conclusions: This study showed the widespread occurrence of all tested enteric virus groups in urban wastewaters. Genetic diversity of astroviruses, enteroviruses and noroviruses in the tropical region was observed. Significance and Impact of the Study: The high prevalence and great genetic diversity of human enteric viruses in urban wastewaters strongly supports the need of further comprehensive studies for evaluating the public health risk associated with viral pathogens in water environments.