MPO and infectious disease: His past medical history included two similar episodes that required hospitalization, the first in April 2021 and subsequently in November 2023 for which infectious diseases workup included negative blood cultures and transesophageal echocardiogram, while immunologic workup was notable for positive c-antineutrophil cytoplasmic antibody (1:160), low C3c (34 mg/dl; normal reference range 82–185 mg/dl), normal C4c, and negative antinuclear antibody, myeloperoxidase, antiproteinase 3, rheumatoid factor, and human leukocyte antigen B27.