Outbreak of Leptospirosis After the Cyclone in Orissa

Background: Two weeks after the cyclone during October-November 1999, several persons in Orissa suffered from a febrile illness with haemorrhagic manifestations. Serum samples from a few such patients tested positive for anti-leptospiral IgM antibodies. We conducted a study in four villages that were flooded after the cyclone to examine the possibility of leptospirosis being the cause of the outbreak.

Methods: One hundred forty-two persons living in four flooded villages in the Jaipur district of Orissa were interviewed for their disease history and possible risk factors after the cyclone. Blood samples were collected and tested for anti-leptospiral antibodies using the microscopic agglutination test, IgM ELISA and lepto-dipstick. Follow up samples were collected from those who had inconclusive results on the first test and the microscopic agglutination test was repeated on these samples.

Results: Eighty-four of the 142 study subjects had suffered a febrile illness and 40 of them had positive results in one or more IgM-based tests and 28 had a positive microscopic agglutination test result as well. Thus, 19.2% of the study subjects (28/142) had serological evidence of symptomatic leptospiral infection after the cyclone. Also, 8.5% of the subjects had low levels of antibodies indicative of the level of background seroprevalence.

Conclusions: The results indicate that there was an outbreak of leptospirosis in the flooded villages and the attack rate was high. A carrier state might have existed in the animal population and the cyclone and floods changed the environment drastically making it conducive for transmission of infection. Large numbers of persons were continuously exposed to flood waters and this resulted in the outbreak.