Urban epidemics of leptospirosis in Salvador, Brazil

Urban epidemics of leptospirosis have emerged to become an important public health problem in Latin America. Although epidemics have been reported from major Brazilian cities since the 1960s, few population-based studies have examined the epidemiologic features of leptospirosis in the urban setting. This dissertation analyzes the pattern of leptospirosis incidence during five years of surveillance at the infectious disease reference hospital in Salvador, Brazil. Patients were consecutively recruited who met a clinical case definition supported by bacteriologic and serologic confirmation. Members of the research Digitized maps of case residence addresses facilitated ecologic analyses of associations between leptospirosis incidence and socioeconomic characteristics of census zones. The temporal relationship between weather and leptospirosis incidence was modeled in a Poisson regression. A serum bank created during the study was used to validate new recombinant-antigen-based serologic tests.; Over a five-year period, more than 1,000 hospitalized patients met the leptospirosis case definition, and the case-fatality ratio was 11.6 percent. Leptospira interrogans Serogroup Icterohaemorrhagiae, associated with rats, was the etiologic agent. Chapter 1 presents the background for the “re-emergence” of epidemic leptospirosis in the urban setting. Chapter 2 describes the cyclical pattern of leptospirosis in the city of Salvador. During annual epidemics, incidence is consistently highest among working-age males living in areas in which a high proportion of households are served by open sewers. Chapter 3 presents a model to predict weekly leptospirosis incidence based on weather patterns during the three preceding weeks. Chapter 4 investigates the effect of a concurrent epidemic of dengue fever on delayed referral of leptospirosis patients during the leptospirosis epidemic in 1996. Chapter 5 evaluates newly developed ELISA assays for the serodiagnosis of leptospirosis, based on five recombinant leptospiral antigens.; This dissertation emphasizes the recurrent and predictable nature of leptospirosis epidemics in a large Brazilian city. The unsanitary conditions associated with high leptospirosis incidence are common in urban slums throughout Latin America. Sanitation infrastructure projects that benefit the population of urban slums are urgently needed to interrupt transmission of Leptospira in this setting.