Date of Award

January 2025

Document Type

Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Albert I. Ko

Abstract

Background: Leptospirosis is a neglected zoonotic disease that disproportionately affects people living in areas with poor sanitation, water contamination and rodent infestation such as urban informal settlements. More than one billion people worldwide reside in such communities, and with increasing urbanization, coupled with environmental change, the risk of Leptospira transmission continues to increase. Despite its global burden, this disease is often underreported due to diagnostic challenges and limited healthcare access, particularly in urban informal settlements. Understanding the incidence and risk factors in these settings is essential for improving public health interventions. This study aims to estimate the annual incidence of Leptospira infection in an urban informal settlement and identify key environmental and social risk factors for infection by Leptospira.

Methods: We conducted a prospective cohort study in Pau da Lima, an urban informal settlement in the city of Salvador, Brazil, from November 2020 to April 2024. Residents were surveyed bi-annually to annually to obtain information on demographics, environmental features and potential risk behaviors. Blood samples were tested for Leptospira exposure using a microscopic agglutination test (MAT). Univariate Generalizing Estimating Equations (GEEs) were used to investigate associations between individual potential risk factors and Leptospira infection. Multivariate Generalized Additive Models (GAMs) were used to investigate associations between risk factors and infection, accounting for household and temporal correlation.

Results: Among 1,800 individuals representing 4,758 person-years of follow-up, we identified serologic evidence for 174 Leptospira infections. The number of infections detected at each follow-up period was as follows: 47 infections in the first follow-up period, 57 infections in the second, 40 infections in the third, and 30 infections in the fourth. We found that infection risk decreased over time, with a notable 42% decrease in risk in the fourth follow-up compared to the first (OR 0.58 [95% CI 0.36–0.92]). Significant risk factors for leptospirosis exposure in multivariate GAMs included male gender (OR 1.71 [95% CI, 1.23–2.37]); age between 35 and 44 (OR 2.94 [95% CI, 1.71–5.06]); age 45 and older (OR 2.24 [95% CI, 1.33–3.78]); and proximity to open sewage (OR 1.52 [95% CI, 1.05–2.19]). The distribution of risk was homogenous within the study site, with no clear spatial effect observed.

Conclusions: These findings highlight the need for targeted public health interventions aimed at high-risk groups such as middle-aged males or people who live near open sewers. Policymakers should prioritize improving sanitation by upgrading residential drainage systems and implementing measures to seal areas exposed to open sewage. Furthermore, provide guidance for residents on initiating small-scale, collaborative community projects, while also launching educational campaigns to raise awareness about the risks of leptospirosis. These campaigns should emphasize the importance of proper hygiene practices and avoiding contact with contaminated water.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 06/16/2026

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