Acinetobacter Baumannii-related Osteomyelitis: Clinical and Epidemiological Characterization

INTRODUCTION Acinetobacter baumannii is an opportunist pathogen that has become increasingly important over recent years as a cause of nosocomial infections (1,2). Ventilator-associated pneumonia, central line-associated bloodstream infection and bone and soft tissue infection secondary to open fractures are among the conditions most associated with this agent.

Attention is drawn not only to the increasing incidence of this agent over the last few years but also to the rapid worsening of its susceptibility to antimicrobial agents, including carbapenems. Among the striking characteristics of this species is its high capacity to develop antimicrobial resistance. The most important types of resistance are, firstly, intrinsic resistance related to the association between diminished permeability of the external membrane and constitutive expression of efflux pumps; and secondly, acquisition of genetic elements, which might be resistance genes or insertion elements that, in association with the chromosomal genes of this bacterium, can trigger expression of resistance and great ability to survive in the environment, which is commonly related to production of biofilm (7). All these characteristics have been correlated with emergence of multiresistant and pan-resistant strains of A. baumannii. Few therapeutic options are available for treating pan-resistant strains: colistin and tigecycline has been used, but resistance to these options frequently emerges in clinical practice. Taking into account the fact that fewer new antimicrobial agents are being validated and introduced into clinical practice, the growing prevalence of isolates with these high levels of resistance is becoming a matter of increasing concern. The formerly abundant flow of provision of new antibiotics of ever-broader spectrum has been shown to be a non-renewable resource.

Certain risk factors have also been correlated with occurrence of A. baumannii. The most important are prolonged hospitalization in intensive care units and use of invasive devices .Another important risk factor is severe trauma: A. baumannii is associated with invasive infections, including osteomyelitis following open fracture reduction. Studies that included military personnel and civilians involved in the recent conflicts in Iraq and Afghanistan have shown high prevalence of A. baumannii as causative agent in cases of osteomyelitis secondary to traumatic injuries. Also, in Brazil, a retrospective study that analyzed 101 cases of osteomyelitis due to Gram-negative bacilli showed that A. baumannii was the second most prevalent agent, showing a high profile of antimicrobial resistance, particularly to carbapenems.

At the Institute of Orthopedics and Traumatology, Hospital das Clínicas, University of São Paulo, a Brazilian reference center that provides care for high-complexity orthopedic cases, 241 cases of osteomyelitis related to A. baumannii were treated between 2007 and 2014. All cases had microbiological confirmation, with positive cultures of bone tissue.

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