TY - JOUR
T1 - Environmental sampling for typhoidal Salmonellas in household and surface waters in Nepal identifies potential transmission pathways
AU - Leboa, Christopher
AU - Shrestha, Sneha
AU - Shakya, Jivan
AU - Naga, Shiva Ram
AU - Shrestha, Sony
AU - Shakya, Mudita
AU - Yu, Alexander T.
AU - Shrestha, Rajeev
AU - Vaidya, Krista
AU - Katuwal, Nishan
AU - Aiemjoy, Kristen
AU - Bogoch, Isaac I.
AU - Uzzell, Christopher B.
AU - Garrett, Denise O.
AU - Luby, Stephen P.
AU - Andrews, Jason R.
AU - Tamrakar, Dipesh
N1 - Funding Information: This work was supported by Bill & Melinda Gates Foundation, Seattle, WA [grant number INV-000572] received by JA, KA, AY and SL (url: https://www.gatesfoundation.org/); and Stanford University Center for Innovation in Global Health Seed Grant received by JA, AY and KA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No authors receive their salary from the funding organizations. Publisher Copyright: © 2023 LeBoa et al.
PY - 2023/10/1
Y1 - 2023/10/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85175609764&partnerID=8YFLogxK
U2 - https://doi.org/10.1371/journal.pntd.0011341
DO - https://doi.org/10.1371/journal.pntd.0011341
M3 - Article
C2 - 37851667
SN - 1935-2727
VL - 17
JO - PLoS neglected tropical diseases
JF - PLoS neglected tropical diseases
IS - 10
M1 - e0011341
ER -