Environmental sampling for typhoidal Salmonellas in household and surface waters in Nepal identifies potential transmission pathways
Issued Date
2023-10-01
Resource Type
ISSN
19352727
eISSN
19352735
Scopus ID
2-s2.0-85175609764
Pubmed ID
37851667
Journal Title
PLoS Neglected Tropical Diseases
Volume
17
Issue
10
Rights Holder(s)
SCOPUS
Bibliographic Citation
PLoS Neglected Tropical Diseases Vol.17 No.10 (2023)
Suggested Citation
Leboa C., Shrestha S., Shakya J., Naga S.R., Shrestha S., Shakya M., Yu A.T., Shrestha R., Vaidya K., Katuwal N., Aiemjoy K., Bogoch I.I., Uzzell C.B., Garrett D.O., Luby S.P., Andrews J.R., Tamrakar D. Environmental sampling for typhoidal Salmonellas in household and surface waters in Nepal identifies potential transmission pathways. PLoS Neglected Tropical Diseases Vol.17 No.10 (2023). doi:10.1371/journal.pntd.0011341 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/91029
Title
Environmental sampling for typhoidal Salmonellas in household and surface waters in Nepal identifies potential transmission pathways
Author's Affiliation
Faculty of Tropical Medicine, Mahidol University
Dhulikel Hospital, Kathmandu
University of California, Berkeley
Toronto General Hospital
University of Toronto
Imperial College London
University of California, Davis
Stanford University
Institute for Research in Science and Technology
Sabin Vaccine Institute
Dhulikel Hospital, Kathmandu
University of California, Berkeley
Toronto General Hospital
University of Toronto
Imperial College London
University of California, Davis
Stanford University
Institute for Research in Science and Technology
Sabin Vaccine Institute
Other Contributor(s)
Abstract
Introduction Salmonella Typhi and Salmonella Paratyphi, fecal-oral transmitted bacterium, have tempo-rally and geographically heterogeneous pathways of transmission. Previous work in Kath-mandu, Nepal implicated stone waterspouts as a dominant transmission pathway after 77% of samples tested positive for Salmonella Typhi and 70% for Salmonella Paratyphi. Due to a falling water table, these spouts no longer provide drinking water, but typhoid fever persists, and the question of the disease’s dominant pathway of transmission remains unanswered. Methods We used environmental surveillance to detect Salmonella Typhi and Salmonella Paratyphi A DNA from potential sources of transmission. We collected 370, 1L drinking water samples from a population-based random sample of households in the Kathmandu and Kavre Districts of Nepal between February and October 2019. Between November 2019 and July 2021, we collected 380, 50mL river water samples from 19 sentinel sites on a monthly inter-val along the rivers leading through the Kathmandu and Kavre Districts. We processed drinking water samples using a single qPCR and processed river water samples using differential centrifugation and qPCR at 0 and after 16 hours of liquid culture enrichment. A 3-cycle threshold (Ct) decrease of Salmonella Typhi or Salmonella Paratyphi, pre-and post-enrich-ment, was used as evidence of growth. We also performed structured observations of human-environment interactions to understand pathways of potential exposure. Results Among 370 drinking water samples, Salmonella Typhi was detected in 7 samples (1.8%) and Salmonella Paratyphi A was detected in 4 (1.0%) samples. Among 380 river water sam-ples, Salmonella Typhi was detected in 171 (45%) and Salmonella Paratyphi A was detected in 152 (42%) samples. Samples located upstream of the Kathmandu city center were positive for Salmonella Typhi 12% of the time while samples from locations in and downstream were positive 58% and 67% of the time respectively. Individuals were observed bathing, washing clothes, and washing vegetables in the rivers. Implications These results suggest that drinking water was not the dominant pathway of transmission of Salmonella Typhi and Salmonella Paratyphi A in the Kathmandu Valley in 2019. The high degree of river water contamination and its use for washing vegetables raises the possibility that river systems represent an important source of typhoid exposure in Kathmandu.