Subacute Bartonella quintana bacteremia following immunomodulatory therapy: a diagnostic challenge.

Bartonella quintana infection presents with a broad clinical spectrum, ranging from asymptomatic to severe disease. Its fastidious growth and immune evasion frequently delay diagnosis, leading to prolonged bacteremia and potential mismanagement. We report a case of subacute Bartonella quintana infection in a patient with newly diagnosed dermatomyositis, presenting with generalized myopathy, persistent low-grade fever, and suspected endocarditis. Blood cultures were intermittently positive, but conventional microbiological methods remained inconclusive. Serology was suggestive, while the definitive diagnosis was established by nanopore sequencing. Combined doxycycline and anti-inflammatory therapy led to rapid clinical improvement. This case highlights the limitations of standard diagnostics for fastidious pathogens and underscores the value of nanopore sequencing for timely diagnosis and targeted management of bloodstream infections.