1. Prepared by Dr. Sintawat Wangsiricharoen (PGY-4) and Dr. Trish Simner

Clinical Vignette

The patient is an adult with past medical history of recurrent Lyme disease including meningitis who presented with several days of fever and altered behavior. According care providers, the patient seems to develop confusion when febrile. The patient also endorses generalized weakness, particularly in the legs. They denied difficulty breathing, cough, urinary discomfort, diarrhea, or rash. Recently, the patient went on a trip to the US North East, where they had no recollection of tick bites and denied sick contacts. At presentation, temperature was 38.1 °C; the remaining vital signs were unremarkable. Neurologic exam showed occasional confusion, but the patient was alert and followed commands. Cranial nerves were intact. Neck was not stiff. Chest was clear to auscultation. Abdomen was soft, nontender, and with no hepatosplenomegaly. Skin exam showed no evidence of rashes or wounds. Labs revealed leukopenia (white blood count 3.39 K/cu mm, reference: 4.50-11.00 K/cu mm, neutrophil 80%, lymphocytes 11%), thrombocytopenia (platelet count 75 K/cu mm, reference: 150-350 K/cu mm), and mildly elevated liver enzymes (AST 50 U/L, reference: 3-37 U/L; ALT 47, reference: 0-40 U/L). A chest X-ray showed clear lung fields without focal airspace consolidation or pleural effusion. Lumbar puncture was not performed due to thrombocytopenia.

Microbiology studies:

Hematologic Wright-Stained Peripheral Thin Smear:

Figure 1: Morulae (blue to purple inclusions) detected in granulocytes on peripheral blood smear.

Question:
Which of the following diagnostic tests should be performed next?