Leptospirosis in a midland rural area of Kerala State.

BACKGROUND & OBJECTIVE Leptospirosis has been repeatedly reported from the State of Kerala since 1989 and is one of the commonest diseases among the 14 notifiable diseases in the district level communicable disease surveillance system. As there are no field studies on human leptospirosis in Kerala, we undertook this seroepidemiological study of leptospirosis in the two hamlets of Ernakulam district in Kerala to identify locally prevalent serogroups, and to understand local epidemiological features of the disease. METHODS Blood samples were collected for five consecutive years from persons willing to subject themselves for the study from the selected areas (Kunnackal and Kunnakkurudy hamlets). Animal studies were conducted among samples from rodents captured from the area by the human volunteers themselves. Antibody titres were determined by microscopic agglutination test (MAT). The investigators inspected all the houses and surrounding land of the study subjects in this period. RESULTS Of the 385 persons enrolled, 29.6 per cent showed evidence of past leptospiral infection. Many locally prevalent serogroups and changing patterns of prevalence in humans were identified in the five consecutive years of the study. The major serogroups were autumnalis, louisiana, australis, and grippotyphosa. Rodents showed 11 per cent seropositivity. Bandicoota indica showed the highest seropositivity (44.4%). INTERPRETATION & CONCLUSION Our findings showed that the physical environment of the study area was favourable for prolonged survival of leptospires. Farming practices exposed the human volunteers to soil and surface water and leptospirosis is endemically present here. Majority of seropositive individuals in the community had only subclinical infection. Rodents were abundant and contributed to enzootic and endemic prevalence of leptospirosis.