Background:

Airborne microbial contamination in operating rooms is an important patient safety concern and may contribute to healthcare-associated infections. Heating, ventilation, and air conditioning (HVAC) systems are essential for controlling airborne microorganisms and particulate matter; however, their effectiveness under routine hospital conditions requires further evaluation.



Methods:

This descriptive-analytical study was conducted in 19 operating rooms of a tertiary teaching hospital during 2022–2023. In total, 171 air samples were collected from supply air diffusers, exhaust grilles, and patient-bed areas using the NIOSH 0800 method. Air changes per hour (ACH), PM₂.₅, PM₁₀, CO₂, temperature, and relative humidity were measured. Associations between bacterial bioaerosol concentrations and environmental variables were analyzed using appropriate statistical tests.



Results:

Bacterial bioaerosol concentrations differed significantly among operating rooms (P < 0.0001), with the highest levels observed in cardiac operating rooms and the lowest in central operating rooms. No significant association was found between ACH and bacterial bioaerosol concentration (r = 0.40, P = 0.09). Bacterial bioaerosol concentration was significantly associated with indoor CO₂ concentration (r = −0.512, P = 0.025), while no significant relationship was observed with temperature (P = 0.60). Particulate matter concentrations varied across operating rooms, with the lowest PM₂.₅ and PM₁₀ levels recorded in central operating rooms.



Conclusion:

ACH alone may not adequately reflect microbial air quality in operating rooms. Integrating microbiological monitoring with ventilation assessment and routine HVAC maintenance may improve indoor air quality, strengthen infection prevention, and enhance patient safety.