Air sampling methods to evaluate microbial contamination in operating theatres: results of a comparative study in an orthopaedics department

units (cfu)/m 2 /h with the IMA method, 123.2 cfu/m 3 with the SAS method and 2768.2 cfu/m 2 /h with the nitrocellulose membranes. Correlation was found between the results of the three methods. Staphylococcus aureus was detected in 12 of 60 operations (20%) with the membranes, five (8.3%) operations with the SAS method, and three operations (5%) with the IMA method. Conclusion: Use of nitrocellulose membranes placed near a wound is a valid method for measuring the microbial contamination of air. This method was more sensitive than the IMA method and was not subject to any calibration bias, unlike active air monitoring systems.