Molecular epidemiology of microbial contamination in the operating room environment: Is there a risk for infection?

Background: Modern operating rooms are considered to be aseptic environments. The use of surgical mask, frequent air exchanges, and architectural barriers are used to reduce airborne microbial populations. Breaks in surgical technique, host contamination, or hematogenous seeding are suggested as causal factors in these infections. This study implicates contamination of the operating room air as an additional etiology of infection.

Methods: To investigate the potential sources of perioperative contamination, an innovative in situ air-sampling analysis was conducted during an 18-month period involving 70 separate vascular surgical procedures. Air-sample cultures were obtained from multiple points within the operating room, ranging from 0.5 to 4 m from the surgical wound. Selected microbial clonality was determined by pulse-field gel electrophoresis. In a separate series of studies microbial nasopharyngeal shedding was evaluated under controlled environmental conditions in the presence and absence of a surgical mask.

Results: Coagulase-negative staphylococci were recovered from 86% of air samples, 51% from within 0.5 m of the surgical wound, whereas Staphylococcus aureus was recovered from 64% of air samples, 39% within 0.5 m from the wound. Anterior nares swabs were obtained from 11 members of the vascular team, clonality was observed between 8 strains of S epidermidis, and 2 strains of S aureus were recovered from selected team members and air-samples collected throughout the operating room environment. Miscellaneous Gram-negative isolates were recovered less frequently (<33%); however, 7 isolates expressed multiple patterns of antimicrobial resistance. The traditional surgical mask demonstrated limited effectiveness at curtailing microbial shedding, especially during symptomatic periods of rhinorrhea.

Conclusions: Gram-positive staphylococcal isolates were frequently isolated from air samples obtained throughout the operating room, including areas adjacent to the operative field. Nasopharyngeal shedding from person participating in the operation was identified as the source of many of these airborne contaminants. Failure of the traditional surgical mask to prevent microbial shedding is likely associated with an increased risk of perioperative contamination of biomedical implants, especially in procedures lasting longer than 90 minutes.