Impact of sampling depth on pathogen detection in pit latrines

• Type of Material: Article
• Authors: Benjamin Risk, Emory University; Drew Capone, Georgia Institute of Technology; Petos Chigwechokha, Malawi University of Science and Technology; Francis L de los Reyes, III, North Carolina State University; Rochelle H Holm, Mzuzu University, Malawi; Elizabeth Tilley, University of Malawi; Joe Brown, Georgia Institute of Technology
• Language: English
• Date: 2021-03-01
• Publisher: PUBLIC LIBRARY SCIENCE
• Publication Version: Final Published Version
• Copyright Statement: © 2021 Capone et al
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1371/journal.pntd.0009176
• Title of Journal or Parent Work: PLOS NEGLECTED TROPICAL DISEASES
• Volume: 15
• Issue: 3
• Start Page: e0009176
• End Page: e0009176
• Grant/Funding Information: This study was funded in part by the Bill and Melinda Gates Foundation (www.gatesfoundation.org) grant OPP1137224 to JB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
• Keywords: Life Sciences & Biomedicine; Tropical Medicine; Infectious Diseases; Science & Technology; Parasitology
• Research Categories: Engineering, Civil; Engineering, Environmental; Environmental Sciences

Abstract

Wastewater based epidemiology (WBE) is increasingly used to provide decision makers with actionable data about community health. WBE efforts to date have primarily focused on sewer-transported wastewater in high-income countries, but at least 1.8 billion people in low-and middle-income countries (LMIC) use onsite sanitation systems such as pit latrines and septic tanks. Like wastewater, fecal sludges from such systems offer similar advantages in community pathogen monitoring and other epidemiological applications. To evaluate the distribution of enteric pathogens inside pit latrines–which could inform sampling methods for WBE in LMIC settings unserved by sewers–we collected fecal sludges from the surface, mid-point, and maximum-depth of 33 pit latrines in urban and peri-urban Malawi and analyzed the 99 samples for 20 common enteric pathogens via multiplex quantitative reverse transcription PCR. Using logistic regression adjusted for household population, latrine sharing, the presence of a concrete floor or slab, water source, and anal cleansing materials, we found no significant difference in the odds of detecting the 20 pathogens from the mid-point (adjusted odds ratio, aOR = 1.1; 95% confidence interval = 0.73, 1.6) and surface samples (aOR = 0.80, 95% CI = 0.54, 1.2) compared with those samples taken from the maximum depth. Our results suggest that, for the purposes of routine pathogen monitor-ing, pit latrine sampling depth does not strongly influence the odds of detecting enteric pathogens by molecular methods. A single sample from the pit latrines’ surface, or a composite of surface samples, may be preferred as the most recent material contributed to the pit and may be easiest to collect.