Background: The diverse tickborne infections of the northeastern United States can present as undifferentiated flu-like illnesses. In areas endemic for Lyme and other tickborne diseases, patients presenting with acute febrile illness with myalgia, headache, neutropenia, thrombocytopenia, and elevated hepatic aminotransferase levels are presumptively diagnosed as having human granulocytic anaplasmosis (HGA).
Objective: To assign a cause for illness experienced by 2 case patients who were initially diagnosed with HGA but did not rapidly defervesce with doxycycline treatment and had no laboratory evidence of Anaplasma phagocytophilum infection.
Design: Case report.
Setting: 2 primary care medical centers in Massachusetts and New Jersey.
Patients: 2 case patients acutely presenting with fever.
Measurements: Identification of the causative agent by polymerase chain reaction and DNA sequencing.
Results: Molecular diagnostic assays detected Borrelia miyamotoi in the peripheral blood of both patients. There was no evidence of infection with other tickborne pathogens commonly diagnosed in the referral areas.
Limitation: One of the case patients may have had concurrent Lyme disease.
Conclusion: The presence of B. miyamotoi DNA in the peripheral blood and the patients' eventual therapeutic response to doxycycline are consistent with the hypothesis that their illness was due to this newly recognized spirochete. Samples from tick-exposed patients acutely presenting with signs of HGA but who have a delayed response to doxycycline therapy or negative confirmatory test results for HGA should be analyzed carefully for evidence of B. miyamotoi infection.