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An 18-month survey was conducted to examine the prevalence of enteric viruses and their relationship to indicators in environmentally polluted shellfish. Groups of oysters, one group per 4 weeks, were relocated to a coastal water area in the Gulf of Mexico that is impacted by municipal sewage and were analyzed for enteroviruses, Norwalk-like viruses (NLV), and indicator microorganisms (fecal coliform, Escherichia coli, and male-specific coliphages). The levels of indicator microorganisms were consistent with the expected continuous pollution of the area. Fourteen of the 18 oyster samples were found by reverse transcription (RT)-PCR to harbor NLV and/or enterovirus sequences. Of the four virus-negative oysters, three had exposure to water temperatures of >29°C. Concomitant with these findings, two of these four oysters also accumulated the lowest levels of coliphages. PCR primers targeting pan-enteroviruses and the NLV 95/96-US common subset were utilized; NLV sequences were detected more frequently than those of enteroviruses. Within the 12-month sampling period, NLV and enterovirus sequences were detected in 58 and 42%, respectively, of the oysters (67% of the oysters tested were positive for at least one virus) from a prohibited shellfish-growing area approximately 30 m away from a sewage discharge site. Eight (4.6%) of the 175 NLV capsid nucleotide sequences were heterogeneous among the clones derived from naturally polluted oysters. Overall, enteric viral sequences were found in the contaminated oysters throughout all seasons except hot summer, with a higher prevalence of NLV than enterovirus. Although a high percentage of the oysters harbored enteric viruses, the virus levels were usually less than or equal to 2 logs of RT-PCR-detectable units per gram of oyster meat. [ABSTRACT FROM AUTHOR]