Clinical Features of Scrub Typhus

TotheEditor—The report by Premaratna et al. [1] is one of several recent publications on scrub typhus to have appeared out of South and Southeast Asia [2–8]. Whether these data provide evidence of a true reemergence of this infection or whether they are just a reflection of reporting bias is unclear, although it is likely that these reports can be attributed to both factors. Regardless, these publications highlight the variable clinical presentation of scrub typhus and the importance of considering scrub typhus as part of the differential diagnosis for patients with nonspecific febrile illnesses in areas in which scrub typus is endemic. These reports also highlight some possible regional differences in clinical presentation. Premaratna et al. [1] remind us that acute hearing loss may occasionally be a clinical feature of scrub typhus. It is important to recognize this largely forgotten complication of scrub typhus, because it is a clear indicator of the diagnosis. However, in many (if not most) cases, scrub typhus presents as an undifferentiated febrile illness. Our recent study, conducted in Nepal, identified 28 cases of scrub typhus in a cohort of 876 febrile adults presenting to an urban hospital [4]. Cases occurred during both winter and summer and in both rural and city dwellers. One-half of these patients had an admission diagnosis of enteric fever, and none were originally considered to have rickettsial infections. Apart from being more likely to be anemic, there were no features that distinguished the patients with scrub typhus from other patients in the study. Of particular note was the absence of an eschar (a classic sign of scrub typhus) or rash in all patients. Although eschars can be difficult to observe, especially among dark-skinned populations, a very low prevalence of eschars (3%–7%) has also been noted in other South Asian studies [2, 6]. This contrasts with findings from studies from elsewhere in Asia, which show eschar prevalences of >60% [7–9]. A recent report from Taiwan highlighted the high prevalence of abnormal liver function among patients admitted to the hospital with scrub typhus [7]. Of 30 patients with scrub typhus, 29 (97%) had liver function abnormalities with high levels of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase. Such findings have not been previously reported, perhaps because liver function has not been systematically evaluated in other studies, although it does raise the possibility of regional variation in clinical presentation of scrub typhus. In our study from Nepal, we recorded liver function abnormalities in 5 (26%) of the 19 patients with scrub typhus who were tested. The lack of diagnostic facilities is also a major reason for the underdiagnosis of scrub typhus. Laboratory diagnosis is mainly reliant on serological tests that are not widely available in regions of endemicity and that have suboptimal sensitivity and specificity, especially when only acute-phase serum samples are available for testing. The introduction of PCR as a diagnostic tool for scrub typhus is promising, although it is unlikely to be a practical option in most resource-poor countries [10]. The development of cheap and simple antigen-detection assays for scrub typhus would be most welcome. Potential conflicts of interest. All authors: no conflicts.