Incidence, microbiological findings, and clinical presentation of sternal wound infections after cardiac surgery with and without local gentamicin prophylaxis

Sternal wound infection (SWI) is a serious complication after cardiac surgery. In a previous randomized controlled trial, the addition of local collagen-gentamicin in the sternal wound before wound closure was found to significantly reduce the incidence of postoperative wound infections compared with the routine intravenous prophylaxis of isoxazolyl-penicillin only. The aims of the present study were to analyse the microbiological findings of the SWIs from the previous trial as well as to correlate these findings with the clinical presentation of SWI. Differences in clinical presentation of SWIs, depending on the causative agent, could be identified. Most infections had a late, insidious onset, and the majority of these were caused by staphylococci, predominantly coagulase-negative staphylococci. The clinically most fulminant infections were caused by gram-negative bacteria and presented early after surgery. Local administration of gentamicin reduced the incidence of SWIs caused by all major, clinically important bacterial species. Propionibacterium acnes was identified as a possible cause of SWI and may be linked to instability in the sternal fixation. There was no indication of an increase in the occurrence of gentamicin-resistant bacterial isolates in the treatment group. Furthermore, the addition of local collagen-gentamicin reduced the incidence of SWIs caused by methicillin-resistant coagulase-negative staphylococci. This technique warrants further evaluation as an alternative to prophylactic vancomycin in settings with a high prevalence of methicillin-resistant Staphylococcus aureus.