Factors influencing microbial colonies in the air of operating rooms

The operating room (OR) of the hospital is a special unit that requires a relatively clean environment. The microbial concentration of an indoor OR extrinsically influences surgical site infection rates. The aim of this study was to use active sampling methods to assess microbial colony counts in working ORs and to determine the factors affecting air contamination in a tertiary referral medical center.

This study was conducted in 28 operating rooms located in a 3000-bed medical center in northern Taiwan. The microbiologic air counts were measured using an impactor air sampler from May to August 2015. Information about the procedure-related operative characteristics and surgical environment (environmental- and personnel-related factors) characteristics was collected.

A total of 250 air samples were collected during surgical procedures. The overall mean number of bacterial colonies in the ORs was 78 ± 47 cfu/m³. The mean number of colonies was the highest for transplant surgery (123 ± 60 cfu/m³), followed by pediatric surgery (115 ± 30.3 cfu/m³). A total of 25 samples (10%) contained pathogens; Coagulase-negative staphylococcus (n = 12, 4.8%) was the most common pathogen. After controlling for potentially confounding factors by a multiple regression analysis, the surgical stage had the significantly highest correlation with bacterial counts (r = 0.346, p < 0.001). Otherwise, independent factors influencing bacterial counts were the type of surgery (29.85 cfu/m³, 95% CI 1.28-58.42, p = 0.041), site of procedure (20.19 cfu/m³, 95% CI 8.24-32.14, p = 0.001), number of indoor staff (4.93 cfu/m³, 95% CI 1.47-8.38, p = 0.005), surgical staging (36.5 cfu/m³, 95% CI 24.76-48.25, p < 0.001), and indoor air temperature (9.4 cfu/m³, 95% CI 1.61-17.18, p = 0.018).

Under the well-controlled ventilation system, the mean microbial colony counts obtained by active sampling in different working ORs were low. The number of personnel and their activities critically influence the microbe concentration in the air of the OR. We suggest that ORs doing complex surgeries with more surgical personnel present should increase the frequency of air exchanges. A well-controlled ventilation system and infection control procedures related to environmental and surgical procedures are of paramount importance for reducing microbial colonies in the air.