Geography and prevalence of rickettsial infections in Northern Tamil
Nadu, India: A cross-sectional study
Abstract
Rickettsial infections and Q fever are a common cause of acute febrile
illness globally. Data on the role of climate and altitude on the
prevalence of these infections in lacking from Southern India. In this
study, we determined the sero-prevalence of scrub typhus (ST), spotted
fever (SF), murine typhus (MT) and Q Fever (QF) in 8 eight geographical
regions of North Tamil Nadu by detecting IgG antbodies using ELISA.
Totally we tested 2565 people from 86 localities. Among the 27.3 %
positives, approximately 5% were IgG positive for two or more
infections. Seroprevalence to rickettsioses and Q fever was highest for
individuals from rural areas and increased with age (>30
years). Those in the Nilgiris highlands (wetter and cooler) and Erode,
which has the most land under irrigation, demonstrated the least
exposure to rickettsioses and Q fever. Lowland plains (AOR: 8.4-22.9;
95% CI: 3.1-55.3) and highland areas upto 1000 metres (AOR: 6.1-10.3;
95% CI: 2.4-23.9) showed the highest risk of exposure to scrub typhus.
For spotted fever, the risk of exposure was highest in Jawadhi
(AOR:10.8; 95% CI: 2.6-44.3) and Kalrayan (AOR:16.6; 95% CI:
4.1–66.2). Q fever positivity was most likely to be encountered in
Salem (AOR: 5.60; 95% CI: 1.01 – 31.08) and Kalrayan hills (AOR:12.3;
95% CI:2.9 – 51.6). Murine typhus risk was significant only in
Thiruvannamalai (AOR:24.2; 95% CI: 3.3 – 178.6). Based on the data
generated it seems that rickettsial infections and Q fever prevalence is
low in areas which receive rainfall of ≥150 cm/yr, with average minimum
and maximum temperatures between 15-25 oC and
elevation in excess of 2000 metres. It is also low in low land and
irrigated lands with dry climate. These preliminary findings need to be
validated by conducting active surveillance in these areas.