Vibrio cholerae and Salmonella Typhi culture-based wastewater or non-sewered sanitation surveillance in a resource-limited region

In resource-limited regions, relying on individual clinical results to monitor community diseases is sometimes not possible. Establishing wastewater and non-sewered sanitation surveillance systems can offer opportunities to improve community health.

We provide our experience of establishing a wastewater and non-sewered sanitation surveillance laboratory in Malawi, a resource-limited region, for Vibrio cholerae and Salmonella serotype Typhi.

Three locations (inclusive of 8 discrete sample collection sites in total) in the Blantyre District were studied for nine weeks, from September 6 to November 1, 2022. Grab samples were collected weekly. We piloted locally available culture-based medical diagnostic methods for V. cholerae and S. Typhi in wastewater, followed by confirmation analysis of the isolates using reverse transcription polymerase chain reaction (RT-PCR).

Bacterial counts ranged from up to 10⁶ colony-forming units/mL for V. cholerae and up to 10⁷ colony-forming units/mL for S. Typhi. RT-PCR of the isolates showed that the available culture-based medical diagnostic methods were successful in detecting V. cholerae but were less accurate for S. Typhi in wastewater.

This experience serves as a catalyst for the development and validation of alternative wastewater surveillance analytical methods that are not dependent solely on RT-PCR. In this field trial conducted in Africa, new data-driven approaches were developed to promote early-level wastewater research and expand analysis options in resource-limited settings. Although culture-based methods are labor-intensive and have some limitations, we suggest initially leveraging the overlap with the locally available medical testing capacity for V. cholerae, whereas S. Typhi with RT-PCR may still be required. Wastewater analysis may be acceptable for V. cholerae and S. Typhi, which have a high degree of clinical case underreporting, fecal shedding, short incubation periods, and clear outbreak trends, predominantly in low- and middle-income countries.