Spatio-temporal analysis of spotted fever cases reported to a tertiary care hospital in Southern India

Spotted fever is caused by spotted fever group rickettsiae (SFGR) belonging to the genus Rickettsia. Transmission to humans occurs primarily through the bite of infected ticks and mites. As a vector-borne disease, the occurrence and distribution of spotted fever is influenced by environmental and climatic factors that support the survival, abundance, and activity of its vectors. This study provides insight on the distribution of spotted fever cases, identifies disease hotspots and demonstrates the seasonality of spotted fever. A clinically suspected case with fever & rash was considered as a case of spotted fever if serology (ELISA/IFA) and/or molecular assays (Nested PCR /qPCR) specific for spotted fever was positive. Demographic data was collected from the electronic medical records. Spatial maps were created using QGIS 3.34.3 software, while, spatial autocorrelation and hotspot analysis was performed using GeoDa version 1.22.0.21. The seasonal trend analysis to depict the peak month of spotted fever cases was undertaken using R software version 4.5.2. In the 18-year dataset (2007–2024), a total of 2,153 suspected patients were tested for spotted fever, of which 516 (24%) were positive. Spatio-temporal analysis revealed that Vellore district reported 39.9% of cases, Chittoor 38.8%, Tirupattur 12.5%, Ranipet 4.5%, and Tiruvannamalai 4.3%. Maximum spotted fever cases were reported between the months of October to March, with a peak in January. Children below 10 years and housewives were at a higher risk of acquiring spotted fever. The findings of this retrospective analysis highlight the importance of considering spotted fever in patients presenting with acute undifferentiated febrile illness with rash, particularly children aged < 10 years, from areas with higher spatial clustering in the cooler months. Prospective studies, preferably multi-centric are needed to confirm the findings and elaborate other factors contributing to occurrence of spotted fever.