Culture-negative osteoarticular infection caused by Legionella sainthelensi

Legionella non-pneumophila species are uncommon causes of human infection and more particularly in extra-pulmonary sites. Osteoarticular involvement remains exceptional and represents a major diagnostic challenge, as routine diagnostic tools are mainly designed to detect L. pneumophila and culture requires specific enriched media. We report a case of severe upper-limb osteoarticular infection caused by Legionella sainthelensi following corticosteroid injection, involving bursitis, deep abscesses and synovitis. Identification was challenging and ultimately achieved through molecular analysis of intra-operative samples, with subsequent confirmation by culture on BCYE agar and MALDI-TOF mass spectrometry. This case highlights the importance of molecular techniques in culture-negative infections with strong clinical suspicion or biological evidences of infection.