Introduction & Objective: The bioaerosol is one of the operating room(OR) hazards that can be threaten of personel health and capable to creating of postoperetive infection in the patients. Because of the hospital infection rate has correleted to bioaerosol concentration, therefore, it is important to determine of type and concentration of these microorganisms as the main goal of this study.    

Materials and Methods: In this research, 23 operation rooms in the 4 educational hospitals of the Hamadan City were studied. 115 air samples were collected in the various locations and conditions according to filtration method suggested by bioaerosol committee of ACGIH. The samples were transported to blood agar and cultivated immediatedly. The type and number of colonies were determined in the laberatory then, the bioaerosol concentration were calculated in terms of cfu/m³. The data of physical conditions of OR_s , ventilation specifications and other environmental parameters have been recorded in the work sheet.

Results: The results have demonstrated that the mean of total bioaerosol and pathogen bioaerosol concentration were 136 cfu/m³ and 4.01 cfu/m³ respectively. The concentration of 25.3% of the total pathogen samples be exceeded of recommended limit. It is apeared that have been correlation between concentration of bioaerosols and duration of surgry (P<0.05), also the concentration of morninig shift were higher than the other shifts(P<0.05).

Conclusion: According to the detected bioaerosols pathogens in the samples, high cleaning class in the operating rooms is necessary. It is necessary to design and administrate the ventilation systems according to standards because of the absence of appropriate ventilation system in the three hospitals of four investigated hospitals.