Methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis rates have decreased over the past 10 years, according to research published in the Journal of Infection. This decrease is “in line” with the reduction in MRSA bacteremia seen in the United Kingdom.

Researchers compared 2 prospective patient cohorts with osteomyelitis who attended the same UK-based bone infection center and were treated 10 years apart. The researchers investigated whether the clinical features of osteomyelitis correlate with microbiology, to quantify the change in osteomyelitis incidence caused by multidrug-resistant organisms over 10 years, and to assess changes in resistance patterns to both “local and systemic empirical antibiotic regimens.”

Patients were surgically treated for osteomyelitis between March 2013 and May 2017. The researchers collected comparative data from a cohort of patients who underwent osteomyelitis surgery between 2001 and 2004.

The 2013 to 2017 cohort included 223 patients with osteomyelitis who were compared with a cohort of 157 patients from 2001 to 2004. In the 2013 to 2017 cohort, the most common osteomyelitis sites were the tibia (44.8%), femur (24.2%), and humerus (12.1%). Less common sites included the forearm, calcaneum, pelvis, ankle, fibula, knee, and clavicle. No microorganism was identified on deep bone culture in 32.3% of patients; 46.1% had monomicrobial infection, and 21.5% had polymicrobial infection. A median of 4.9 deep-tissue specimens were sent for microbiologic culture, and 87.4% of patients has at least 5 samples analyzed. The most common isolate was Staphylococcus aureus (37.5%), 10.5% of which was MRSA.

Multidrug-resistant pathogens were identified in 15.2% of infections in the 2013 to 2017 cohort and in 17.1% of infections in the 2001to 2004 cohort. Adjusted logistic regression models assessed cohort, history of metalwork, site of infection, age, and sex and did not demonstrate an association of odds of developing multidrug-resistant infection with treatment period. In addition, the researchers observed that the proportion of MRSA isolated was lower in the 2013 to 2017 cohort than in the 2001 to 2004 cohort (11.4% vs 30.8%, respectively; P =.007); however, no significant difference was noted between S aureus multidrug-resistant isolates among the 2 cohorts, according to the number of methicillin-sensitive isolates.

Univariate but not multivariate analyses found that multidrug-resistant infection was associated with metalwork in situ (P =.03 and P =.06, respectively). The estimated odds ratio for multidrug-resistant infection in the setting of metalwork in situ was 5.0 (95% CI, 1.15-22.0).

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Limitations to the study included possible confounding between metalwork and cause of infection, as well as variation in minimum inhibitory concentration breakpoints defining resistance in the 2001-2004 and 2013-2017 cohorts.

“In our centre, we have seen a reduction in MRSA osteomyelitis to almost one third of the proportion observed 10 years ago,” the researchers concluded. “The possible association with pre-operative decolonization therapy, suggested by the absence of MRSA infection in patients with iatrogenic infection, merits further investigation.”

Reference

Dudareva M, Hotchen AJ, Ferguson J, et al. The microbiology of chronic osteomyelitis: changes over ten years. J Infect. 2019;79(3):189-198.