Etiology and antimicrobial resistance patterns in chronic osteomyelitis of the tibia: an 11-year clinical experience.

PURPOSE: To analyze changes in tendency of etiology and of antimicrobial resistance patterns to most common local and systemic antibiotics in chronic osteomyelitis of the tibia (COM-T) in a Level I trauma center over an 11-year period.

METHODS: A retrospective review including all patients with COM-T who were surgically treated from January 2009 to December 2019. Patients were divided into two period groups: 2009-2014 and 2015-2019. Microbiologic etiology was analyzed. Bacterial resistance patterns evaluation was based on the Magiorakos et al. classification, including proportions of multidrug-resistant organisms (MDROs, acquired non-susceptibility to at least one agent in three or more antimicrobial categories), extensively drug-resistant (XDR) and pan drug-resistant (PDR) organisms encountered.

RESULTS: A total of 173 episodes of COM-T were identified. Monomicrobial infections represented 47.4% of all cases, while 28.3% had polymicrobial infections. Negative deep-bone cultures were identified in 24.3% of the patients. The most commonly isolated microorganisms were coagulase-negative Staphylococci (24.5%) and S. aureus (20.5%). No differences were found when comparing Gram-positive infections between periods (58.3% for 2009-2014 vs. 46.7% for 2015-2019; p = 0.10). Findings were similar for Gram-negative infections (37% vs. 33.7%; p = 0.62), although more polymicrobial infections were detected (24.7% vs. 33.3%, respectively; p = 0.359). MDROs were involved in 15% of the cases, with an upward trend when comparing both periods (12.8% vs. 23.6%; p = 0.07). The most-used combination of local antibiotics-glycopeptide (vancomycin) plus aminoglycoside (gentamicin or tobramycin)-was met with low rates of resistance in the most frequently isolated microorganisms.

CONCLUSION: According to the results of the present study, rates of Gram-positive and Gram-negative infections remained consistent during the two study periods, but with an upward trend in MDRO and polymicrobial infections detected. The local combination of a glycopeptide plus an aminoglycoside was effective in treating the most frequently isolated microorganisms.