Antimicrobial efficacy of preoperative skin antisepsis and clonal relationship to postantiseptic skin-and-wound flora in patients undergoing clean orthopedic surgery

Nosocomial surgical site infections (SSI) are still important complications in surgery. The underlying mechanisms are not fully understood. The aim of this study was to elucidate the possible role of skin flora surviving preoperative antisepsis as a possible cause of SSI. We conducted a two-phase prospective clinical trial in patients undergoing clean orthopedic surgery at a university trauma center in northern Germany. Quantitative swab samples were taken from pre- and postantiseptic skin and, additionally, from the wound base, wound margin, and the suture of 137 patients. Seventy-four patients during phase I and 63 during phase II were investigated. Microbial growth, species spectrum, and antibiotic susceptibility were analyzed. In phase two, the clonal relationship of strains was additionally analyzed. 18.0 % of the swab samples were positive for bacterial growth in the wound base, 24.5 % in the margin, and 27.3 % in the suture. Only 65.5 % of patients showed a 100 % reduction of the skin flora after antisepsis. The microbial spectrum in all postantiseptic samples was dominated by coagulase-negative staphylococci (CoNS). Clonally related staphylococci were detected in ten patients [nine CoNS, one methicillin-susceptible Staphylococcus aureus (MSSA)]. Six of ten patients were suspected of having transmitted identical clones from skin flora into the wound. Ethanol-based antisepsis results in unexpected high levels of skin flora, which can be transmitted into the wound during surgery causing yet unexplained SSI. Keeping with the concept of zero tolerance, further studies are needed in order to understand the origin of this flora to allow further reduction of SSI.