Wastewater-based epidemiology and quantitative microbial risk assessment associated with wastewater contact of norovirus in Bangkok, Thailand

Abstract

Norovirus is one of the leading causes of acute gastroenteritis worldwide. Wastewater surveillance offer significant benefits such as enhancing our understanding of the disease occurrence in the population, evaluating the effectiveness of pathogen reduction in the treatment process, and tracking the spread of pathogens in the environment which pose a health risk to humans. Hence, wastewater surveillance is crucial. In this study, the influent and effluent samples were collected bi-monthly from March 2020 to March 2021 from three distinct wastewater treatment plants in Bangkok. Wastewater samples were concentrated and subjected to quantitative polymerase chain reaction (qPCR) to assess norovirus concentrations. Additionally, microbial indicators, coliform bacteria and coliphage, were evaluated using cell culture methods. Concentration of E. coli and total coliform in the influent and effluent ranged from 4.04 – 5.03 log CFU/mL and 2.64 – 3.76 log CFU/ml, respectively. Concentration of coliphage in the influent and effluent ranged from 1.76 log PFU/ml and 0.42 log PFU/ml, respectively. Average concentrations of norovirus GI and GII were (1.90 and 1.35 log copies/ml) and (0.91 and 0.37 log copies/ml) in the influent and effluent, respectively. Removal efficiency for microbial indicators was 1.26 – 1.40 log CFU, PFU/ml while the removal of norovirus GI and GII were 0.75 and 0.54 log copies/ml. Seasonal variations were observed, with the highest concentrations of microorganisms during the rainy season and the highest norovirus concentration in winter. An epidemiological comparison between norovirus concentrations from wastewater treatment plants and reported norovirus cases showed similar patterns, suggesting that wastewater could serve as a useful tool for detecting infections within a population, particularly when clinical data are limited. Effluent samples were used to determine the Spearman’s correlation between the microbial indicators and both norovirus strains. Our analysis found that these microbial indicators could not represent norovirus due to low correlation (rs < 0.3). Additionally, the effluent was also used to assess the probability of illness with acute gastroenteritis from exposure to wastewater by quantitative microbial risk assessment from fishing activities and small craft boating. Exposure to effluent from the system, the probability of both activities had a median probability of illness below 0.036. Despite the ability of wastewater treatment plants to reduce the number of microorganisms, the treated wastewater still harbored these microorganisms presenting a potential health risk if discharged into public water sources or used in activities. Efficient wastewater treatment systems are recommended to be developed, including disinfection methods, to mitigate the risks from waterborne pathogens.