Alternative fecal indicators and their empirical relationships with enteric viruses, Salmonella enterica, and Pseudomonas aeruginosa in surface waters of a tropical urban catchment.

The suitability of traditional microbial indicators (i.e., Escherichia coli and enterococci) has been challenged due to the lack of correlation with pathogens and evidence of possible regrowth in the natural environment. In this study, the relationships between alternative microbial indicators of potential human fecal contamination (Bacteroides thetaiotaomicron, Methanobrevibacter smithii, human polyomaviruses [HPyVs], and F+ and somatic coliphages) and pathogens (Salmonella spp., Pseudomonas aeruginosa, rotavirus, astrovirus, norovirus GI, norovirus GII, and adenovirus) were compared with those of traditional microbial indicators, as well as environmental parameters (temperature, conductivity, salinity, pH, dissolved oxygen, total organic carbon, total suspended solids, turbidity, total nitrogen, and total phosphorus). Water samples were collected from surface waters of urban catchments in Singapore. Salmonella and P. aeruginosa had significant positive correlations with most of the microbial indicators, especially E. coli and enterococci. Norovirus GII showed moderately strong positive correlations with most of the microbial indicators, except for HPyVs and coliphages. In general, high geometric means and significant correlations between human-specific markers and pathogens suggest the possibility of sewage contamination in some areas. The simultaneous detection of human-specific markers (i.e., B. thetaiotaomicron, M. smithii, and HPyVs) with E. coli and enterococcus supports the likelihood of recent fecal contamination, since the human-specific markers are unable to regrow in natural surface waters. Multiple-linear-regression results further confirm that the inclusion of M. smithii and HPyVs, together with traditional indicators, would better predict the occurrence of pathogens. Further study is needed to determine the applicability of such models to different geographical locations and environmental conditions.

Risk assessment of noroviruses and human adenoviruses in recreational surface waters.

In the interest of public health and safety, this study aimed to quantify risks associated with the presence of noroviruses (NoV) and human adenoviruses (HAdV) in an urban catchment area in Singapore. Enteric viruses were quantified using QPCR. NoV were more prevalent in water samples than HAdV, and presented higher associated illness risks across all exposure scenarios. For primary contact recreation of adults and children, mean probability of illness were 0.0061 and 0.0089 for NoV, and 0.0028 and 0.0048 for HAdV. For secondary contact recreation, mean probability of illness were 0.0016 for NoV and 0.00068 for HAdV. Therefore, owing to their prevalence and associated risks, NoV are better suited as reference pathogens in recreational waters in Singapore.

Evaluation of FRNA coliphages as indicators of human enteric viruses in a tropical urban freshwater catchment.

This study aimed to evaluate the relationship between FRNA coliphages (FRNA GI to GIV) and human enteric viruses (human adenoviruses, HAdV, astroviruses, AstV, noroviruses, NoV, and rotaviruses, RoV) in a tropical urban freshwater catchment. Positive associations between human-specific coliphages and human viral pathogens substantiate their use as viral indicators and in microbial source tracking. Reverse transcription qPCR was used to measure the concentrations of viruses and FRNA coliphages in concentrated water samples. Environmental water samples were also analyzed for male-specific (F+) and somatic (Som) coliphages using plaque assay. The most abundant enteric virus was NoV (55%) followed by HAdV (33%), RoV (33%), and AstV (23%), while the most abundant FRNA genogroup was GI (85%) followed by GII (48%), GIV (8%) and GIII (7%). Concentrations of human-specific coliphages FRNA GII were positively correlated with NoV, HAdV, RoV, AstV, F+ and Som (τ = 0.5 to 0.3, P < 0.05) while concentrations of animal-specific coliphages FRNA GI were negatively correlated with HAdV and RoV (τ = -0.2, P < 0.05). This study demonstrates statistical relationships between human-specific coliphages and a suite of human enteric viruses in the environment.

Surveillance of enteric viruses and coliphages in a tropical urban catchment.

An assessment of the occurrence and concentration of enteric viruses and coliphages was carried out in highly urbanized catchment waters in the tropical city-state of Singapore. Target enteric viruses in this study were noroviruses, adenoviruses, astroviruses and rotaviruses. In total, 65 water samples were collected from canals and the reservoir of the Marina catchment on a monthly basis over a period of a year. Quantitative PCR (qPCR) and single agar layer plaque assay (SAL) were used to enumerate target enteric viruses and coliphages in water samples, respectively. The most prevalent pathogen were noroviruses, detected in 37 samples (57%), particularly norovirus genogroup II (48%), with a mean concentration of 3.7 × 10(2) gene copies per liter. Rotavirus was the second most prevalent virus (40%) with a mean concentration of 2.5 × 10(2) GC/L. The mean concentrations of somatic and male-specific coliphages were 2.2 × 10(2) and 1.1 × 10(2) PFU/100 ml, respectively. The occurrence and concentration of each target virus and the ratio of somatic to male-specific coliphages varied at different sampling sites in the catchment. For sampling sites with higher frequency of occurrence and concentration of viruses, the ratio of somatic to male-specific coliphages was generally much lower than other sampling sites with lower incidences of enteric viruses. Overall, higher statistical correlation was observed between target enteric viruses than between enteric viruses and coliphages. However, male-specific coliphages were positively correlated with norovirus concentrations. A multi-level integrated surveillance system, which comprises the monitoring of bacterial indicators, coliphages and selected enteric viruses, could help to meet recreational and surface water quality criteria in a complex urbanized catchment.