Serological evidence of spotted fever group rickettsiosis in and around Puducherry, south India-A three years study.

Background & objectives: Rickettsial diseases are important re-emerging infections that mostly go unnoticed or are misdiagnosed. Though few case reports of Indian tick typhus have been reported in Indian literature in the past 10 yr, prevalence surveys are few and far between. The objective of this research was to study the seroprevalence of spotted fever (SF) group rickettsiosis and its coinfection with scrub typhus (ST) in Puducherry region of south India, as these two diseases may show similar clinical presentations.

Methods: During 2012-2015, paired sera of 320 febrile patients were examined for Rickettsia conorii IgM/IgG by ELISA and OX19 and OX2 agglutinins by Weil-Felix test. Additionally, patients were screened for ST IgM ELISA. Statistical analysis was performed for clinical and laboratory parameters in children and adults using Fisher's exact test and chi-square test with Yates correction.

Results: Out of 320 patients, 142 (44.38%) had R. conorii IgM and/or IgG antibodies. Only IgM was present in 72 (22.5%) patients, while 36 patients were positive for IgG only and 34 were positive for both IgG and IgM. A total of 68 patients (21.25%) showed only OX19 and/or OX2 antibodies (titres ≥ 1 : 80). SF and ST coinfection was observed in 47 cases (14.69%).

Interpretation & conclusion: Seroprevalence of SF in Puducherry was found to be quite high (44.38%). ST and SF coinfection was observed in 34.50% of the SG IgG positive patients, however, this require further evaluation by PCR to rule out cross-reaction or false positivity. At present ELISA seems to be an affordable alternative to highly subjective and technically demanding immunofluorescence assay (IFA) for serodiagnosis of SF.