Acute Coxiella burnetii infection presenting as sepsis with multisystem involvement in an immunosuppressed patient: a case report.

Q fever, caused by Coxiella burnetii, rarely presents as severe disseminated disease, and timely diagnosis can be difficult because clinical manifestations are nonspecific and routine microbiological tests are often unrevealing. We report a 68-year-old man with rheumatoid arthritis receiving long-term immunosuppressive therapy who presented with persistent unexplained fever, pancytopenia, hepatic dysfunction, polyserosal effusions, and sepsis with multisystem involvement, without a clear epidemiological exposure history. Blood cultures and routine respiratory pathogen testing were negative. Peripheral-blood metagenomic next-generation sequencing (mNGS) detected C. burnetii nucleic acid sequences, and subsequent antibody testing and targeted qPCR supported the diagnosis of acute Q fever with disseminated manifestations. Doxycycline-based targeted therapy was followed by defervescence and marked clinical and laboratory improvement. This case suggests that, in selected immunocompromised patients with severe infection and persistently negative conventional investigations, mNGS may serve as an adjunctive tool to facilitate timely pathogen identification and guide targeted antimicrobial therapy.