Multiple studies have demonstrated the presence of microorganisms commonly associated with surgical site infections (SSIs), in the air within the operating theatre (OT). In some countries such Italy, the limit of microbial concentration in the air for OT with turbulent airflows is 35 CFU/m3 for an empty OT and 180 CFU/m3 during activity. This study aims to hypothesize new benchmarks for the airborne microbial load in turbulent airflow operating theatres in operational and at rest conditions using the percentile distribution of data through a 17-year environmental monitoring campaign in various Italian hospitals that implemented a continuous quality improvement policy. The quartile distribution analysis has shown how in operational and at rest conditions, 75% of the values were below 110 CFU/m3 and 18 CFU/m3, respectively, which can be considered a new benchmark for the monitored OTs. During the initial stages of the monitoring campaign, 28.14% of the concentration values in operational conditions and 29.29% of the values in at rest conditions did not conform to the Italian guidelines' reference values. In contrast, during the last 5 years, all values in both conditions conformed to the reference values and 98.94% of these values were below the new benchmarks. Continuous improvement has allowed contamination to be reduced to levels well below the current reference values.
Keywords: benchmark for microbial airborne concentration; surgical site infections; turbulent airflow operating theatres.