No correlation between skin microbial counts after preoperative skin disinfection and surgical site infections

Abstract number: P1455

Tschudin S., Egli-Gany D., Dangel M., Oertli D., Weber W., Frei R., Widmer A.F.

Objectives: Preoperative skin disinfection as outlined by WHO is standard practice for the prevention of surgical site infections (SSI), yet few studies examined the association between skin microbial flora after disinfection and the development of a SSI. No study examining an association between skin microbial counts and a subsequent infection has so far been completed in a large sample compromised of a variety of surgical patients.

Therefore we examined the correlation between total colony forming unit counts of skin flora after preoperative skin disinfection at surgical incision site and the development of a subsequent SSI in patients from different surgical specialties.

Methods: Prospective observational study in which 1014 skin cultures immediately were taken from patients after preoperative skin disinfection, before incision. Disinfection of the surgical site was performed according to the study protocol, using standardized procedure under supervision of a study nurse or the attending surgeons. Skin swabs were incubated for 48 hours and colony forming units (cfu) were enumerated and identified by means of standard laboratory identification methods. The finding of more than 10 cfu was regarded as significant colonization. The diagnosis of SSI was based on surveillance, full chart review and postdischarge surveillance (30 days after surgery) using the Centers for Disease Control/National Nosocomial Infection Surveillance (CDC/NNIS) definitions.

Results: 1014 skin cultures from surgical sites were taken from a total of 1005 patients, mainly receiving orthopedic or cardiac surgery. 36 (3.6%) cultures revealed significant colonization of the preoperative site after skin disinfection. Coagulase-negative staphylococcus was the most common organism detected (83.3%), followed by S. aureus (8,3). 41 SSIs were detected accounting for a surgical site infection rate of 4.0%. Most SSIs occurred in cardiac surgery (34.2%). Significant cfu counts after skin disinfection were not correlated with SSI (Table).

Conclusion: This large study was not able to establish a correlation between residual colonization and SSI, indicating that a standardized three step disinfection is sufficient to prepare the surgical site.

Residual cfu after disinfection	Rate of SSI
<10	3, 8%
10	0, 2%