Research Article: Household Transmission of Leptospira Infection in Urban Slum Communities

Date Published: January 30, 2008

Publisher: Public Library of Science

Author(s): Elves A. P. Maciel, Ana Luiza F. de Carvalho, Simone F. Nascimento, Rosan B. de Matos, Edilane L. Gouveia, Mitermayer G. Reis, Albert I. Ko, Mathieu Picardeau

Abstract: BackgroundLeptospirosis, a spirochaetal zoonotic disease, is the cause of epidemics associated with high mortality in urban slum communities. Infection with pathogenic Leptospira occurs during environmental exposures and is traditionally associated with occupational risk activities. However, slum inhabitants reside in close proximity to environmental sources of contamination, suggesting that transmission during urban epidemics occurs in the household environment.Methods and FindingsA survey was performed to determine whether Leptospira infection clustered within households located in slum communities in the city of Salvador, Brazil. Hospital-based surveillance identified 89 confirmed cases of leptospirosis during an outbreak. Serum samples were obtained from members of 22 households with index cases of leptospirosis and 52 control households located in the same slum communities. The presence of anti-Leptospira agglutinating antibodies was used as a marker for previous infection. In households with index cases, 22 (30%) of 74 members had anti-Leptospira antibodies, whereas 16 (8%) of 195 members from control households had anti-Leptospira antibodies. Highest titres were directed against L. interrogans serovars of the Icterohaemorrhagiae serogroup in 95% and 100% of the subjects with agglutinating antibodies from case and control households, respectively. Residence in a household with an index case of leptospirosis was associated with increased risk (OR 5.29, 95% CI 2.13–13.12) of having had a Leptospira infection. Increased infection risk was found for all age groups who resided in a household with an index case, including children <15 years of age (P = 0.008).ConclusionsThis study identified significant household clustering of Leptospira infection in slum communities where recurrent epidemics of leptospirosis occur. The findings support the hypothesis that the household environment is an important transmission determinant in the urban slum setting. Prevention therefore needs to target sources of contamination and risk activities which occur in the places where slum inhabitants reside.

Partial Text: Leptospirosis is an important zoonotic health problem because of its life-threatening clinical manifestations, Weil’s disease and severe pulmonary haemorrhage syndrome, for which fatality is 10 to 50% [1]. Moreover there has been growing awareness of the large under-recognized disease burden that leptospirosis imparts in developing countries [2]. Leptospirosis is an environmentally-transmitted disease. Pathogenic spirochetes of the genus Leptospira establish chronic carriage in the kidney tubules of wild and domestic mammalian reservoirs and persist for weeks in the environment after excretion from the host [3]. The major mode of transmission to humans is indirect contact with water or moist soil contaminated with the urine of animal reservoirs [3]. Leptospirosis is associated with a spectrum of environmental settings and risk exposures. Recreation, travel and water sports have become significant risk factors in industrialized countries [3],[4],[5], as exemplified by outbreaks during triathlon and adventure tourisms events [6],[7]. In developing countries situated in tropical climates, leptospirosis is an endemic disease of rural-based populations engaged in subsistence farming, sharecropping and animal husbandry [3],[8].

Active surveillance detected an outbreak of severe leptospirosis in Salvador during the seasonal period of heavy rainfall in 2001. Between March and October, 124 suspected cases were identified which resided within the city whereas 16 cases were identified during the preceding four month period. Leptospirosis cases were residents of 70 slum neighbourhoods (bairros) situated within the city. Cases were mostly adults (mean age±standard deviation, 35.2±13.5 years) and males (86% of 124 cases) and hospitalized with manifestations of Weil’s disease such as jaundice (77% of 124 cases) and acute renal failure (73% with serum creatinine >2.0 mg/dL). Overall case fatality was 10% (12 of 124 deaths). Among the 124 suspected cases, 89 (72%) had a laboratory-confirmed diagnosis of leptospirosis.

This study, performed in an endemic region for urban leptospirosis, identified household clustering of Leptospira infection within slum communities. Among members who resided in the same household as an index case of leptospirosis, 30% had evidence of a previous infection as determined by the presence of anti-Leptospira antibodies in the MAT. These individuals had more than five times the risk for acquiring anti-Leptospira antibodies as compared with members of neighbouring households. Household clustering of Leptospira infection has not been found in surveys which evaluated for this phenomenon in rural endemic settings [22]. A previous serologic survey, which was also performed in Salvador and used IgM ELISA to detect anti-Leptospira antibodies, found that high (41%) proportions of children had antibodies among those residing in households with index cases of leptospirosis [23]. However, a control group was not evaluated in order to assess whether individuals with anti-Leptospira antibodies specifically aggregated in index case households. This study, as far as we are aware, is the first to describe household clustering of Leptospira infection.