Yield of routine mycobacterial culture of osteoarticular specimens in a tertiary orthopaedic hospital in England, 2017-2022.

Introduction: At our tertiary orthopaedic centre, mycobacterial cultures are routinely performed on bone and joint samples sent for bacterial culture. Methods: From laboratory records, we ascertained the number of mycobacterial cultures performed, the number positive for Mycobacterium tuberculosis complex (MTBC) and/or non-tuberculous mycobacteria (NTM), and the characteristics of individuals from whom mycobacteria were isolated. We collected the same data from 100 individuals with negative mycobacterial cultures. Results: Excluding sample types that were not bone or joint samples, 6162 mycobacterial cultures were performed between 4 July 2017 and 30 September 2022. A total of 22 patients had MTBC and 6 patients had NTM newly isolated from bone or joint samples placed in mycobacterial culture, while a further 1 patient had both Mycobacterium tuberculosis and Mycobacterium avium isolated. To identify one new mycobacterial infection of bone or joint (MTBC or NTM) that would not have been detected with routine bacterial cultures alone, 229 (95 % CI of 158-347) mycobacterial cultures were needed. Mycobacterial cultures were much less likely to be positive in samples taken from prosthetic joints. They were more likely to be positive in spinal samples and in samples taken from patients with suspected sarcoma. In patients from whom MTBC had been isolated, granulomatous inflammation was reported in 86 % (18 of 21) of contemporaneous histological specimens. Conclusions: Targeted, rather than routine, mycobacterial culture of bone and joint specimens should be considered in settings with a low burden of tuberculosis.