Osteoarticular Infection by Mycobacterium bovis Following Intravesical Bacillus Calmette-Guérin (BCG) Therapy: A Rare Case of Septic Arthritis and Osteomyelitis in an Immunocompromised Host

Osteoarticular infections caused by <i>Mycobacterium bovis</i> are rare complications associated with intravesical Bacillus Calmette-Guérin (BCG) therapy and often cause subtle, nonspecific symptoms, which can delay the diagnosis and treatment. We present the case of a 72-year-old male with a history of urothelial carcinoma treated with intravesical BCG therapy administered four years earlier, who developed persistent fever and progressive worsening polyarthralgia with a two-month duration prior to hospital admission. Imaging presented extensive joint and soft tissue inflammatory involvement. Early microbiological studies remained inconclusive, and the patient required several surgical debridements and broad-spectrum antimicrobial therapy empirically, later escalated to include antimycobacterial coverage. Definitive identification of a <i>Mycobacterium bovis</i> was obtained through genomic sequencing of synovial and bone specimens. A nine-month course of isoniazid, rifampicin, and ethambutol was initiated, leading to progressive clinical improvement. Bacillus Calmette-Guérin-related osteoarticular infections are challenging conditions due to their rarity, insidious course, and usually the absence of microbiological confirmation by standard methods, especially in immunocompromised patients. Early suspicion, timely recognition, use of targeted microbiological tests, and a multidisciplinary approach are essential to achieve favorable outcomes.