Clinico-laboratory profile of scrub typhus cases among adults presenting with acute febrile illness

To determine the frequency and clinico-epidemiological profile of patients with scrub typhus and to assess the performance characteristics of an ICT based rapid assay for its diagnosis.

This was an observational cross-sectional study conducted on 175 adults ≥18 years of age presenting with acute onset of fever (temperature >38 °C) for <14 days with any of the following features: eschar, rash, lymphadenopathy, hepatosplenomegaly, jaundice and multi-organ involvement. Immunocompromised patients, such as those with HIV/AIDS, malignancy, patients on cytotoxic drugs and on systemic corticosteroid therapy were excluded from the study. Cases were recruited from medicine wards of Lok Nayak Hospital. Serum from the cases was tested for Orientia tsutsugamushi specific IgM antibody by ELISA and rapid assay. The performance characteristics of rapid assay was evaluated by comparing it with ELISA as the reference standard.

Out of 175 cases, 36 (20.6 %) were reactive for scrub typhus IgM ELISA, while 139 (79.4 %) were non-reactive. Maximum number of scrub typhus cases were in the age group of 21-30 years (41.7 %) with both genders affected equally. Majority of the scrub typhus cases resided in urban areas (69.4 %), belonged to lower middle class (38.9 %) and were seen between the monsoon months of July and October (75 %). Eschar, lymphadenopathy, jaundice, ascites, ARDS, myocarditis, DIC, raised LDH, raised ALP, hyperbilirubinemia, hyperphosphatemia, hypoalbuminemia and leucocytosis were found to be significantly associated with scrub typhus. The sensitivity and specificity of the scrub typhus IgM rapid assay when compared to IgM ELISA was 22.2 % and 100.0 %, respectively, with low kappa value of 0.312.

The frequency of scrub typhus in AFI was found to be 20.6 %. In view of the poor sensitivity, the RDT used in our study cannot be recommended as the screening assay for serodiagnosis of scrub typhus.