Transient False-Reactive Fourth-Generation HIV Screening and Delayed Warm Autoimmune Hemolytic Anemia Following Acute Babesia microti Infection in an Asplenic Patient

Babesiosis is a tick-borne infection caused by intraerythrocytic Babesia species and may be associated with both direct hemolysis and uncommon immune-mediated complications.We describe a 47-year-old man with asplenia who presented with acute Babesia microti (B.microti) infection and 2.21% parasitemia.During the acute illness, a fourth-generation Elecsys HIV Duo HIV-1/2 antigen/antibody screening assay was reactive, while HIV-1/HIV-2 antibody differentiation testing was negative and HIV-1 RNA was not detected (<20 copies/mL).Repeat HIV testing after clinical recovery was negative, supporting a transient false-reactive screening result.Approximately two weeks after the initial hospitalization, the patient developed warm autoimmune hemolytic anemia (WAHA), with hemoglobin declining from 14.1 to 8.8 g/dL, reticulocytosis, markedly elevated lactate dehydrogenase, low haptoglobin, and a positive direct antiglobulin test with IgG 2+ and C3d negative.He improved with prednisone 60 mg daily without transfusion, rituximab, or intravenous immunoglobulin.This case highlights two unusual phenomena occurring in temporal association with acute B. microti infection and underscores the importance of confirmatory HIV testing and vigilance for delayed autoimmune hemolysis, particularly in asplenic patients.