Microbial air monitoring in operating theatres: experience at the University Hospital of Parma

Background: Microbial air monitoring in operating theatres has been a subject of interest and debate. No generally accepted sampling methods and threshold values are available.

Aim: To assess microbial air contamination in empty and working conventionally ventilated operating theatres over a three-year period at the University Hospital of Parma, Italy.

Methods: Air sampling was performed in 29 operating theatres. Both active and passive sampling methods were used to assess bacterial and fungal contamination.

Findings: In empty theatres, median bacterial values of 12 colony-forming units (cfu)/m(3) [interquartile range (IQR) 4-32] and 1 index of microbial air contamination (IMA) (IQR 0-3) were recorded. In working theatres, these values increased significantly (P < 0.001) to 80 cfu/m(3) (IQR 42-176) and 7 IMA (IQR 4-13). Maximum recorded values were 166 cfu/m(3) and 8 IMA for empty theatres, and 798 cfu/m(3) and 42 IMA for working theatres. Combining active and passive samplings, fungi were isolated in 39.13% of samples collected in empty theatres and 56.95% of samples collected in working theatres. Over the three-year study period, bacterial contamination decreased in both empty and working theatres, and the percentage of samples devoid of fungi increased. In working theatres, a significant correlation was found between the bacterial contamination values assessed using passive and active sampling methods (P < 0.001).

Conclusion: Microbiological monitoring is a useful tool for assessment of the contamination of operating theatres in order to improve air quality.