Definitive diagnoses of acute hepatitis A and scrub typhus can be established by serologic tests for hepatitis A IgM and indirect immunofluorescent antibody assays or PCR for O. tsutsugamushi. However in developing or third-world countries in the Far East or Southeast Asia, the aforementioned tests are often unavailable. Therefore, this study was conducted to identify easily available markers from clinical and routine laboratory findings that are useful in differentiating hepatitis A from scrub typhus.
Among clinical findings, eschar and rash were identified in 97% and 88.3% of the patients in the scrub typhus group, respectively, whereas they were observed in none of the patients in the hepatitis A group. These findings suggest that that these two clinical findings might be helpful in identifying scrub typhus and hepatitis A. However, there was no eschar and skin rash in hepatitis A population, and we believed it was unreasonable to include these variables in the analysis because odd ratios could not be obtained. Thus, we excluded these variables in final multivariate logistic regression.
Silpapojakul and others reported that eschars were observed in 7% of dark-skinned children in Thailand.11 In contrast, eschars are observed frequently in yellow-skinned children in Japan.12 In children in Thailand, eschars are relatively difficult to detect because of darker skin, and when the eschars are atypical at the early stage they are easily overlooked. In countries in Southeast Asia such as Thailand, where scrub typhus and hepatitis A are endemic, differentiation between scrub typhus and hepatitis A is difficult in cases where eschars or rashes do not occur. Therefore, we attempted to identify markers from laboratory findings that would distinguish scrub typhus from hepatitis A.
At presentation, an AST level ≥ 40 U/L was observed in 98.1% of the patients in the hepatitis A group and 89.8% of those in the scrub typhus group. An ALT level ≥ 40 U/L was observed in 98.1% of the patients in the hepatitis A group and in 74.6% of those in the scrub typhus group. However, an ALT level ≥ 500 U/L was observed in only 1% (2 patients) of the patients in the scrub typhus group (1 patient had an ALT level ≥ 1,000 U/L) compared with 87.5% of the patients in the hepatitis A group. Moreover, 80 (76.9%) patients in the hepatitis A group had an ALT level ≥ 1,000 U/L. A bilirubin level ≥ 1.3 mg/dL was found in 90.4% of patients with hepatitis A and in 33% of patients with scrub hepatitis. Multiple logistic analysis confirmed ALT ≥ 500 U/L and bilirubin ≥ 1.3 mg/dL as independent predictive factors for hepatitis A. We believe that these findings will be useful in differentiating scrub typhus from hepatitis A.