Objectives: To determine the difference, if any, between the reduction of bacteria on contaminated normal skin and contaminated superficially abraded skin following standard surgical preparations at clinically relevant time points after injury.
Design: Prospective animal study.
Setting: Laboratory.
Subjects: Thirty-two New Zealand white rabbits.
Intervention: Two sites, two by two centimeters, one abraded and one nonabraded (control), were studied on each rabbit. Both were inoculated with encapsulated Staphylococcus aureus strain Wood 46. Four six-millimeter punch biopsies were obtained after inoculation, immediately before surgical scrub, and five minutes and then two hours after completion of the surgical scrub. The rabbits were divided into four cohort groups with surgical scrubs performed at six, twelve, twenty-four, and forty-eight hours after inoculation. Bacterial counts were determined.
Main outcome measurements: Numbers of bacteria on surgical sites.
Results: Before surgical preparation, the amount of bacteria on the normal skin (control sites) dropped significantly (p<0.02) except in the six-hour group (p<0.20). At the abraded skin sites, the bacteria flourished. The surgical scrub dropped bacterial counts at both the abraded and nonabraded skin sites significantly (p<0.05) except for the abraded site in the twenty-four-hour group (p<0.08). However in the twelve-, twenty-four-, and forty-eight-hour groups, the bacterial counts (colony-forming units) were still markedly elevated (>1x10(5) at abraded sites) when compared with the nonabraded skin sites (p<0.008) at the respective time intervals. Only at the six-hour interval were the bacterial counts reduced similarly at both the abraded and nonabraded skin sites.
Conclusions: In a rabbit model the standard surgical preparation using povidone-iodine at six hours after inoculation is effective in reducing the bacterial count on abraded skin to that of surgically prepared nonabraded skin. Beyond that time, the standard surgical preparation is ineffective in reducing counts to those of nonabraded skin at similar time intervals.