Human Granulocytic Anaplasmosis Diagnosed Based on a Peripheral Blood Smear Test in South Korea: a Case Report

We report a case of human granulocytic anaplasmosis (HGA) in a 76-year-old woman, diagnosed rapidly based on the characteristic peripheral blood smear finding of intragranulocytic morulae. The smear was prepared on the day of hospitalization, which was 1-2 weeks before results of the serology test or polymerase chain reaction (PCR) became available. Owing to the blood smear test, we could start timely and appropriate antimicrobial treatment. The sensitivity of peripheral blood smear is lower compared to that of serology or PCR for the diagnosis of HGA but may increase with the examiner's experience. In our case, the diagnosis of HGA was confirmed based on PCR and serology 7 and 14 days after the positive peripheral blood smear test, respectively. Morulae in neutrophils are a diagnostic indicator of HGA, particularly for febrile patients with a history of tick bites or outdoor activities in rural areas.