Abstract / Summary
Abstract A 43-year-old man presented with recurrent fever for one week, unresponsive to initial antibiotics. Blood mNGS detected Coxiella burnetii , confirming Q fever. After partial improvement with moxifloxacin-doxycycline and discharge, follow-up Brucella tube agglutination test (SAT) at 10 days post-discharge rose to 1∶100 (++++). Combined with a slaughterhouse exposure history, concurrent brucellosis was diagnosed. Doxycycline plus trimethoprim-sulfamethoxazole for 6 weeks achieved complete recovery. Initial SAT was equivocal (1∶50) with negative IgM/IgG, risking missed diagnosis. mNGS only identified C. burnetii , not Brucella, demonstrating false negatives from low nucleic acid load. Doxycycline-based therapy without a second agent was insufficient, necessitating regimen adjustment. Our patient, who purchased beef at a slaughterhouse and personally cut and packaged it one month before onset, represents a classic, easily overlooked urban exposure route. Conclusions: A single mNGS-detected pathogen does not exclude co-infection in exposed patients. Dynamic serology is essential to avoid missed diagnoses of concurrent Q fever and brucellosis.