A hospital based survey for rickettsioses in Shimoga, Karnataka using the Weil-Felix test

Abstract

Background: Members of the genus Rickettsiae are transmitted by ticks, mites and lice to humans. The rickettsial agents are important causes of fever. Clinical diagnosis of rickettsial fevers is difficult and laboratory support is necessary to confirm the etiology. Mortality is 30-40% in untreated cases. The Weil-Felix test has been traditionally used to detect rickettsial antibodies in sera. However, the test has poor sensitivity. Despite availability of newer modalities of diagnosis, many laboratories offer only the Weil-Felix test for diagnosing rickettsial fevers. Objectives: To obtain information about the types of rickettsial fevers present in Shimoga, Karnataka, using the Weil-Felix test. Methods: 277 patients with undiagnosed fever of seven days or more were included in the prospective study. Sera were subjected to a panel of tests to screen for common infectious etiologies including rickettsiae. Only the (exclusively) Weil-Felix positive sera were considered for the study. Serum samples testing positive for any other infectious disease with/ without detectable rickettsial antibodies were not studied further. Results of the Weil-Felix test were analyzed. Results: Of the total 277 samples, 87 (31.4%) were positive for rickettsial antibodies. Spotted fevers (34.50%) and the scrub typhus (25.30%) are the commonest rickettsioses. Typhus fevers are also present (17.25%). Younger males were more frequently seen to have rickettsial fever, but this could be a fallacy. Weil-Felix test could not detect antibodies in 71 (27.8%) clinically suspected rickettsial fever samples. Conclusions: In Shimoga, Karnataka, spotted fever, scrub typhus and typhus fevers are present. The Weil-Felix test despite having limitations remains useful at present. More studies need to be conducted at the community level in Shimoga district, Karnataka to get a clearer picture of the types of rickettsia and the magnitude of the problem. Keywords: Karnataka, Rickettsia, Scrub typhus, Shimoga, S