Clinical prediction of endemic rickettsioses in northern Taiwan--relevance of peripheral blood atypical lymphocytes.

BACKGROUND AND PURPOSE

Several rickettsioses are endemic in Taiwan. They are under-reported not only because of ignorance but also due to difficulty in recognition caused by their nonspecific manifestations, which overlap with other acute febrile illnesses. We conducted a retrospective study to delineate distinctive clinical features of rickettsiosis, in order to develop a system for differential diagnosis of rickettsiosis.

METHODS

Patients admitted to Chang Gung Memorial Hospital Linkou Medical Center, Taoyuan, Taiwan, with suspected rickettsiosis during the period from January 2004 to May 2006 were included. Clinical suspicion was based on the presence of acute fever with eschar formation, relevant contact history, poor response to broad-spectrum empiric antibacterial therapy, unexplained thrombocytopenia, leukopenia, or abnormal liver biochemistry, or unexplained major organ involvement. Serum samples were sent to the Centers for Disease Control, Taiwan, for serologic diagnosis of the 3 rickettsioses endemic to Taiwan - scrub typhus (Tsutsugamushi's disease), murine typhus (endemic typhus) and Q fever. Serologically confirmed and excluded cases were compared for signs and symptoms, risk factors, laboratory findings and response to treatment.

RESULTS

Among 138 suspected cases, 88 were excluded from the study because of incomplete serological tests or insufficient information, 28 were confirmed to have one of the 3 rickettsioses and 22 were negative for all of them. Distinct features among confirmed cases, compared to controls, were eschar formation, relevant contact history, and presence of atypical lymphocytes in peripheral blood. Normal or low leukocyte count, thrombocytopenia and relative bradycardia were not significant in predicting diagnosis. We propose a predictive system for tentative diagnosis of rickettsiosis based on relevant clinical attributes. This system has a positive predictive value of 80% and a negative predictive value of 100%.

CONCLUSIONS

The predictive scoring system may allow institution of appropriate treatment for rickettsiosis in a more timely manner. However, a low probability of diagnosis should prompt vigorous search for other etiologies.