Risk factors associated with the seroprevalence of leptospirosis, amongst at-risk groups in and around Tanga city, Tanzania.

The epidemiological status of human leptospirosis in Tanzania has not been well defined because of a general lack of awareness of the disease and difficulties in its diagnosis. A cross-sectional seroprevalence study, using the microscopic agglutination test with a threshold titre of 1 : 160, was therefore conducted, among various occupational groups from Tanga city, in November 2005. Of the 199 subjects investigated, 30 (15.1%) were found to have antibodies that reacted with antigens from at least one of the six Leptospira interrogans serovars used in the agglutination test. Of the seropositive samples, 36.6% were positive for serovar Icterohaemorrhagiae, 30.0% for Bataviae, 20.0% for Hardjo, 6.6% for Tarrassovi, 3.3% for Ballum and 3.3% for Pomona. Amongst the occupational groups examined, livestock farmers, veterinary/meat inspectors and abattoir workers appeared to be most at risk, with seroprevalences of 19.4%, 18.1% and 17.1%, respectively. Subjects who reported that they milked cows were significantly more likely to be found seropositive for Leptospira infection than the other subjects (odds ratio=3.44; P<0.001). These findings indicate that a significant proportion of the population of Tanga city is being exposed to pathogenic Leptospira. Public-health interventions against leptospirosis will need to target not only the occupational groups considered to be at high risk of infection but also the general population at large.