Infrastructure risk factors for leptospirosis transmission in urban informal settlements

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ABSTRACT Leptospirosis is a globally important environmentally transmitted disease, with approximately one million cases and 60,000 deaths reported annually. In low-income urban communities, inadequate sanitation, drainage and waste management may increase human exposure to contaminated environments. This study investigated the influence of environmental engineering risk factors on Leptospira exposure in four disadvantaged urban communities (favelas) in Salvador, Brazil. A high-precision georeferenced field survey was developed to identify, map and characterise sanitation, stormwater drainage and solid waste infrastructure. Cross-sectional spatial analyses of baseline data were used to assess associations between environmental risk factors and the residential locations of individuals with anti- Leptospira antibodies. Seropositive individuals tended to reside closer to environmental risk factors and at lower relative elevations. Density analyses indicated that seropositive individuals tended to reside closer to inadequate or partially adequate sewerage components than to sewage-contaminated streams or open sewage points. Inadequate streets showed also showed high density peaks, suggesting that exposure may occur through frequent contact with contaminated runoff and standing water. In contrast, open waste dumping sites and vacant lots showed weaker and more diffuse spatial patterns. The findings highlight the importance of infrastructure quality shaping leptospirosis risk within urban informal settlements. The proposed methodology provides a practical approach for high-resolution characterisation of environmental exposure pathways and may support targeted engineering interventions and epidemiological investigations of leptospirosis and other environmentally transmitted diseases. AUTHOR SUMMARY Leptospirosis is transmitted through contact with water or soil contaminated by pathogenic Leptospira . In densely populated urban communities, inadequate sanitation, drainage, streets and waste management may create multiple exposure pathways. However, methods for assessing these conditions in sufficient detail remain limited. We developed a systematic field methodology using high-precision georeferencing to identify, map and assess environmental engineering risk factors in four disadvantaged urban communities in Salvador, Brazil. We examined these conditions in relation to the homes of residents with evidence of previous exposure to Leptospira bacteria. Previously exposed residents tended to live closer to inadequate or partially adequate sewerage components and inadequate streets, and at lower elevations relative to their surroundings. Waste-disposal sites and vacant lots showed less distinct patterns. Our findings show that detailed, high-precision mapping of infrastructure conditions can identify potential environmental exposure pathways that broader assessments of sanitation may overlook. This practical and reproducible methodology can support epidemiological studies of leptospirosis and other diseases transmitted through contaminated environments and help identify locations where infrastructure improvements may reduce human exposure.

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