Urban Onsite Sanitation Upgrades and Synanthropic Flies in Maputo, Mozambique: Effects on Enteric Pathogen Infection Risks

• Published in: Environmental science & technology 2023-01, Vol.57 (1), p.549-560
• Main Authors: Capone, Drew, Adriano, Zaida, Cumming, Oliver, Irish, Seth R., Knee, Jackie, Nala, Rassul, Brown, Joe
• Format: Article
• Language: English
• Subjects: Animals; Bacteria; Diptera; E coli; Ecotoxicology and Public Health; Escherichia coli; Fecal coliforms; Feces; Flies; Food; Food consumption; Food contamination; Food contamination & poisoning; Giardia; Health risks; Infections; Intervention; Life Sciences; Microorganisms; Mozambique; Onsite; Pathogens; Polymerase chain reaction; Reverse transcription; Risk assessment; Sanitation; Sanitation systems
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.2c06864

Synanthropic filth flies transport enteric pathogens from feces to food, which upon consumption poses an infection risk. We evaluated the effect of an onsite sanitation interventionincluding fly control measuresin Maputo, Mozambique, on the risk of infection from consuming fly-contaminated food. After enumerating flies at intervention and control sites, we cultured fecal indicator bacteria, quantified gene copies for 22 enteric pathogens via reverse transcription quantitative polymerase chain reaction (RT-qPCR), and developed quantitative microbial risk assessment (QMRA) models to estimate annual risks of infection attributable to fly-contaminated foods. We found that the intervention reduced fly counts at latrine entrances by 69% (aRR = 0.31, [0.13, 0.75]) but not at food preparation areas (aRR = 0.92, [0.33, 2.6]). Half of (23/46) of individual flies were positive for culturable Escherichia coli, and we detected ≥1 pathogen gene from 45% (79/176) of flies, including enteropathogenic E. coli (37/176), adenovirus (25/176), Giardia spp. (13/176), and Trichuris trichiura (12/176). We detected ≥1 pathogen gene from half the flies caught in control (54%, 30/56) and intervention compounds (50%, 17/34) at baseline, which decreased 12 months post-intervention to 43% (23/53) at control compounds and 27% (9/33) for intervention compounds. These data indicate flies as a potentially important mechanical vector for enteric pathogen transmission in this setting. The intervention may have reduced the risk of fly-mediated enteric infection for some pathogens, but infrequent detection resulted in wide confidence intervals; we observed no apparent difference in infection risk between groups in a pooled estimate of all pathogens assessed (aRR = 0.84, [0.61, 1.2]). The infection risks posed by flies suggest that the design of sanitation systems and service delivery should include fly control measures to prevent enteric pathogen transmission.