Abstract
Current sewage treatment processes fail to protect against viral contamination of the marine environment and human enteric viruses are frequently present in sewage effluents. Chief amongst these are the Noroviruses (NoV), which are responsible for virtually all outbreaks of gastroenteritis. NoVs are non-cultivable, and molecular methods for their environmental detection are relatively new. Consequently, virtually nothing is known about their survival in the environment. This project seeks to determine the occurrence of NoVs in crude sewage effluents, their behaviour during passage through sewage treatment processes, and their subsequent survival characteristics in the marine environment. Current NoV detection methods are dependent on qualitative reverse transcription PCR (RT-PCR), however survival studies require quantitative methods. Within this study, a quantitative PCR assay for NoVs in sewage effluents has been developed using the real-time TaqMan assay. Data demonstrate that NoVs are ubiquitous in effluent samples, with higher titres present within winter months. Viruses were poorly inactivated by treatment and were still present at high titre in final (secondary) effluent. NoVs were detected in 75% of final effluents tested. In contrast, E.coli was approximately tenfold more sensitive to inactivation/removal by treatment. Sunlight was found to be an important factor in virus inactivation within seawater, whilst decreased temperature favored survival. All E.coli inactivation times were dramatically quicker than viruses, notably NoV and on average NoV demonstrated longer survival times than any organism. Overall, it was judged that conventional bacterial indicators of sewage treatment efficacy and bathing water standards do not adequately reflect the survival of viruses during treatment or in the marine environment.