A river in crisis: water quality, microbial burden, and public health implications of a South African urban river

Abstract

This study evaluated water quality, microbial contamination, and public health implications of a South African urban river. Water samples were collected monthly over 12 months from five sites and analyzed for physico-chemical parameters and microbial indicators (total coliforms and Escherichia coli). Salmonella, Shigella, and Vibrio cholerae were enumerated using culture-based methods and confirmed with real-time PCR targeting the invA, ipaH, and toxR genes. The β-Poisson dose-response model estimated the probability of infection (Pi) following ingestion of 1 mL, 16 mL, and 37 mL of river water during baptism, swimming by adults and non-adults, respectively. Average values for pH, temperature, and total dissolved solids were 7.29, 18˚C, and 160 mg/L, respectively. The total coliform and E. coli counts exceeded 2,000 and 400 CFU/100 mL at most sites. Mean bacterial counts (Log CFU/100 mL) in dry and rainy seasons were 3.22 ± 0.88; 3.28 ± 0.97 for Salmonella, 4.60 ± 0.53; 4.45 ± 0.79 for Shigella, and 0.73 ± 1.97; 3.27 ± 2.24 for Vibrio cholerae. Estimated Pi from ingesting 1 mL of water ranged from 2.57% to 24.73, 4.91%-15.99%, and 1.44%-19.5% for Salmonella, Shigella, and V. cholerae, respectively, increasing with the volume ingested and frequency of exposure. Site C, located within a densely populated urban informal settlement, posed the highest infection risk. Our findings highlight the substantial public health risk from this urban river and reinforce the urgent need for improved water quality management and public health interventions to protect vulnerable communities. In addition, results from this study underscore the need for a One Health Approach for enteric pathogen surveillance in South Africa.

Importance: Urban rivers in low- and middle-income countries are essential for domestic, religious, and recreational use but often pose significant public health risks. This study quantified microbial contamination and assessed the infection risk from accidental ingestion of water from a South African urban river. Total coliform and Escherichia coli counts consistently exceeded safe limits, with high levels of Salmonella, Shigella, and Vibrio cholerae. Infection probabilities of up to 25% for a single exposure, ingesting 1 mL of river water, were noted, which increased with ingested volume and multiple exposures. Risk of infection was higher at sites alongside informal settlements, highlighting the impact of socioeconomic inequities and poor sanitation infrastructure. These findings underscore the urgent need for improved water quality management and integrated One Health surveillance of enteric pathogens to mitigate exposure risks and safeguard vulnerable populations.

Keywords: Jukskei River; feacal contamination; public health risk; quantitative microbial risk assessment; water quality.

Fig 1

Map showing the five sampling sites A–E (red dots) along the Jukskei River (blue line) in Johannesburg, South Africa. Site A (business district): 26,18147°S, 28,10237°E, site B (recreational park): 26,16475°S, 28,13029°E, site C (densely populated informal settlement): 26,08208°S, 28,10873°E, site D (residential suburb): 26,06715°S 28,10767°E, and site E (Golf Estate): 25,98690°S, 27,99731°E. The map was created using ArcGIS software.

Fig 2

Mean counts for Salmonella sp., Shigella sp., and Vibrio cholerae across the five sampling sites throughout the study period. *Statistically significant between sampling sites when P < 0.05. For Salmonella sp., significant differences were found between site B and C (P = 0.014), sites C and E (P < 0.001), and sites D and E (P = 0.001). For Shigella sp., statistically significant differences were between sites A and C (P = 0.045), sites B and C (P = 0.027), and sites C and E (P = 0.034). For Vibrio cholerae, significant differences were between sites A and C (P = 0.025), sites B and C (P = 0.006), sites B and D (P = 0.044), and sites C and E (P = 0.017).