Factors associated with the sero-prevalence of Rickettsioses in Northern Tamil Nadu, India.

Introduction: Rickettsial infections are vector borne diseases and seroprevalence shows regional and population based variation. This prospective study assesses the seroprevalence and factors associated with rickettsial infections in different geographical regions of Northern Tamil Nadu, India. Methods: A community based cross sectional study was performed among 2565 individuals in five districts in Tamil Nadu who consented and provided 4 ml blood samples. A semistructured questionnaire was administered to gather information on sociodemographic and environmental parameters. The serum IgG antibodies to scrub typhus (ST), spotted fever (SF), murine typhus (MT) and Q fever (QF) were detected by ELISA and the optical density (OD) recorded. EpiData was used for data entry and SPSS for analysis. Results: The seroprevalence of ST, SF, MT and QF was 14%, 9.1%, 3.7%, and 5.7%, among the study population. For ST, age >35, people living in rural and <1000 MSL, farmers, sleeping on the floor, lack of toilet at home, and grass near the home were associated with higher risk. For SF, people living at 501 to 1000 MSL elevation, no toilet at home and having pet animal were associated with higher odds. Females, 46 to 55 and >65 years, people residing in urban areas and elevation upto 500 MSL, those who sleep on the floor, not changing clothes daily and with pet at home were associated with higher odds of MT. Whereas Q fever was more likely to affect who sleep directly on the floor, residing in urban and do not have pets. Conclusion: Scrub typhus is the most common rickettsial infection followed by spotted fever in Northern Tamil Nadu. Factors associated with prevalence vary for different rickettsial diseases and include personal and lifestyle behaviors. The findings of this study need to be verified by multicentre cohort studies.