The microbiology of chronic osteomyelitis in a developing world setting

Abstract

OBJECTIVES: The primary aim of this study was to identify the microorganisms that cause chronic osteomyelitis in a developing world clinical setting and to characterise the antibiotic sensitivity profile of these pathogens. Furthermore, we aimed to determine whether the causative organisms vary in relation to physiological status of the host, the HIV status of the patient or the cause of the infection (post-traumatic, post-operative and haematogenous. METHODS: We performed a retrospective review of consecutive adult patients treated curatively for chronic osteomyelitis of long bones, over a two-year period. Patient charts were reviewed and data extracted in respect of patient demographics, the cause of infection, physiological status of the host in accordance with the Cierny and Mader classification, HIV status, surgical treatment strategy and causative organism. RESULTS: A total of 108 organisms were identified in the 60 patients included in the study. Multiple organism were cultures in 45% of patients, a single Gram-positive organism in 22% and a single Gram-negative organism in 26% of patients. In four cases (7%) no causative organism was cultured. The most prevalent organisms were Enterobacteriaceae (34%), Staphylococcus spp. (29%), Pseudomonas aeruginosa (11%), and Enterococcus spp. (9%). Many isolates were found to be resistant to commonly used empirical anti-microbial agents. Seventy per cent of Enterobacteriaceae spp. were resistant to either cefuroxime and/or ampicillin-clavulanic acid. Seventy-seven per cent of Staphylococcus aureus isolates were susceptible to cloxacillin. More than 50% of Pseudomonas aeruginosa strains were resistant to meropenem, imipenem, piperacillin-tazobactam or cefepime. There was a significant association between the aetiology of the infection and the microorganisms involved (p-value < 0.01). The bacterial pathogen profile was, however, not associated with the physiological status of the host (p=0.22) or the HIV status of the patient. CONCLUSION: While the majority of haematogenous chronic osteomyelitis still involved a solitary Gram-positive organism, the incidence of Gram-negative infections was found to be higher than previously reported. Contiguous chronic osteomyelitis was mostly polymicrobial in nature and solitary infections involving a Gram-negative organism was most common in the post-traumatic group. The bacterial pathogen did not vary in relation to the HIV status of the patient or the physiological status of the host.