Risk factors associated with leptospirosis during an outbreak in Middle Andaman, India.

BACKGROUND & OBJECTIVE Leptospirosis outbreaks occur frequently in North and South Andaman Islands but not in Middle Andaman. In 2002, an outbreak appeared in Middle Andaman for the first time. Although a study on risk factors was conducted in North Andaman, it used seropositivity to define leptospirosis. Since seropositivity might not indicate current leptospiral infection and as no study on risk factors was conducted in Middle Andaman, we carried out this study to identify the risk factors during the outbreak. METHODS A suspected outbreak of leptospirosis occurred in Rangat of Middle Andaman during October - November 2002. Suspected cases were screened for leptospirosis using microscopic agglutination test (MAT). Fifty two patients confirmed to have leptospirosis based on rising titres in MAT on paired sera, and 104 age, sex and neighbourhood seronegative matched controls, were included in the study. A conditional multiple regression by backward elimination process was carried out with acute leptospirosis as the dependent factor and various environmental, occupational and behavioural factors as independent factors. A stratified analysis was also carried out. RESULTS The presence of cattle in the house, drinking stream water, contact with garbage, walking barefoot and standing in water while working were identified as significant factors associated with leptospirosis. Stratified analysis showed a dose response relationship between number of cattle in the house and the risk of leptospiral infection suugesting that cattle could be a source of infection. INTERPRETATION & CONCLUSION Identification of the potential risk factors would help understand the transmission dynamics of the disease and formulate public health interventions.