RISK-FACTORS IN THE TRANSMISSION OF LEPTOSPIRAL INFECTION

An unmatched case control study was conducted to study the various ris k factors for acquiring leptospiral infection in Diglipur tehsil of No rth Andaman. A random sample of 1014 persons residing in various villa ges of Diglipur was inducted into the study. Serum samples were collec ted from them and tested for anti-leptospiral antibodies using microsc opic agglutination test (MAT) using Leptospira grippotyphosa, L. austr alis, L. canicola and L. icterohaemorrhagiae antigens. Persons with a titre of 1:50 or more were considered as the cases (550) and the seron egatives as controls (464). Information about 30 variables relating to household characteristics, occupation, contact with animals and behav ioural factors was collected by interviewing the subjects. The prevale nces of these variables in both the groups were calculated and the odd s ratio with 95 per cent confidence intervals were computed. The serop revalence rate was found to increase linearly with age and it was sign ificantly higher in males. None of the risk factors studied had any as sociation with seropositivity to serovar L. icterohaemorrhagiae. For t he other serovars, some form of recent exposure to outdoor environment had significant association. Other factors which had association with infection with specific serovars included use of well or stream water and presence of dogs in the house for infection with L;. grippotyphos a, farming families and presence of cattle in the houses for infection with L. australis and the habit of bathing in ponds for infection wit h L. canicola. These observed associations can be taken as clues of th e transmission cycles and would help in guiding further investigations for understanding the epidemiology of leptospirosis in these islands.