AIMS:  To study prevalence of scrub typhus (ST) meningoencephalitis among cases of Acute Encephalitis Syndrome (AES) and  identify differentiating features from other AES.

METHODS:  Hospital based prospective observational study in tertiary care public hospital in northern India.  Consecutive patients admitted on 2  predecided week days were enrolled over one year if they satisfied predefined inclusion criteria, and subjected to standardized work up. IgM against Orientia tsutsugamushi was tested in serum using commercial ELISA kit.  Clinical and laboratory features were compared between IgM positive and negative patients by univariate and logistic regression analysis.   Weil Felix test was validated against IgM ELISA.

RESULTS:  Of 148 patients enrolled, IgM ELISA for ST was positive in 29 (19.5%). Mean duration of fever was longer and rash, eschar and hepatomegaly were significantly more common in ST group.  Among laboratory parameters, total blood leucocyte count (TLC), total cerebrospinal fluid protein and serum  transaminase levels were significantly higher in ST group, while serum albumin and platelet count were lower.  On logistic regression, hepatomegaly, higher TLC and lower platelet count emerged as significant independent ‘predictors’ of ST.  No patient had focal neurological deficits.  Sensitivity of Weil Felix test was 48.2% , specificity 58.8%.

CONCLUSION: ST  is an important cause of AES in this region. Hepatomegaly, low platelets and raised TLC are significant ‘predictors’ of ST. A combination of these features may help physicians working in peripheral areas to suspect ST. Weil Felix test is not sufficiently sensitive or specific.