Continuous Presence of Noroviruses and Sapoviruses in Raw Sewage Reflects Infections among Inhabitants of Toyama, Japan (2006 to 2008)

Abstract

Various genotypes of norovirus (NoV) (genogroup I genotype 1 [GI.1], -2, -4, -5, -8, -11, -12, and -14; GII.3, -4, -6, -7, -10, -13, -14, and -15), and sapovirus (SaV) (GI.1 and GI.2, GII.1, and GIV.1) were detected from raw sewage from April 2006 to March 2008, while limited numbers of genotypes of NoV (GI.8, GII.4, GII.6, and GII.13) and SaV (GII.3 and GIV.1) and of NoV (GII.4, GII.7, and GII.13) were detected from clinical cases and healthy children, respectively. During the winter 2006 to 2008, a large number of sporadic gastroenteritis outbreaks and many outbreaks caused by NoV GII.4 occurred among inhabitants in Toyama, Japan. The copy number of genomes of NoV GII detected from raw sewage changed in relation to the number of outbreaks. NoV strains of the same genotypes observed in both raw sewage and human specimens belonged to the same cluster by phylogenetic analysis and had almost identical nucleotide sequences among each genotype. These data suggest that NoVs and SaVs detected from raw sewage reflect the viruses circulating in the community, irrespective of symptoms, and that subclinical infections of NoV are common in Japan. Combined surveys of raw sewage with those of clinical cases help us to understand the relationship between infection of these viruses and gastroenteritis.

Detection and Genetic Analysis of Human Sapoviruses in River Water in Japan

“…The genetic analysis of SaVs in environmental samples, such as wastewater, river water, clams, and oysters, has been reported previously (3,9,11,18). The present study provides additional evidence for the genetic diversity of human SaVs in river water.…”

“…The nested RT-PCR assay, number 3 shown in Table 3, had the highest amplification efficiency among the RT-PCR assays tested. Although some previous studies have attempted to identify SaV sequences in environmental samples, such as wastewater, river water, and clams, by conventional RT-PCR (number 1 or 2 in Table 2) (9,11,18), the sensitivity is low and the detection from environmental samples might be underestimated in these studies. Human SaV sequences were frequently detected in winter, from November to March, whereas none were obtained in April, July, September, or October ( Table 3).…”

“…Since SaVs have been detected from fecal samples of infected patients (6,17,19,25,26,29,30) and environmental samples such as wastewater, river water, clams, and oysters (3,9,11,16,18), it is believed that SaVs are transmitted from person to person via fecal-oral routes and through contaminated foods and water. Caliciviruses, namely, SaVs and noroviruses (NoVs), are included in the latest U.S. Environmental Protection Agency's Contaminant Candidate List (CCL 3), a list of emerging contaminants that may pose a public health risk in water environments (27).…”

Frequent Detection of Noroviruses and Sapoviruses in Swine and High Genetic Diversity of Porcine Sapovirus in Japan during Fiscal Year 2008

“…Porcine NoVs might have acquired genetic stability compared to human NoVs, which were also detected in this study. The number of NoV outbreaks in the human population increases in winter (15). In 2008, NoVs GII/3 and GII/13 in addition to GII/4 were included in the major causes of human outbreaks in Toyama prefecture (our unpublished observation).…”

Comprehensive Analysis of a Norovirus-Associated Gastroenteritis Outbreak, from the Environment to the Consumer

“…Similar to other viruses causing gastroenteritis, NoVs multiply in the intestines and are excreted in large quantities in human feces. Human waste is processed in sewage treatment plants, but the treatment procedures do not completely remove enteric viruses from the water effluents leaving the plant (8,16). Strains that cause severe symptomatic infections as well as those that cause subclinical infections are excreted into sewage, which may then be discharged into coastal environments (11).…”