Aerosol Bioburden and Antimicrobial Resistance in Orthopaedic Operating Unit in a Tertiary Hospital in Thailand

Objective: This study aimed to determine the microbial indoor air quality and factors associated with bacterial air contamination in the orthopaedic operating unit. Materials and Methods: Conducted in seven operating rooms (ORs) and six surrounding rooms (SRs) in an orthopaedic operating unit. A total of 352 air samples were collected using an Andersen air sampler. Fungal and bacterial counts were determined as air quality indicators. Antimicrobial resistance (AMR) of predominant bacteria and factors influencing microbial air quality were analyzed. Results: Most air samples in the ORs (87.2%) and SRs (81.8%) contained acceptable fungal counts. However, unoccupied ORs (11.1%), occupied ORs (58.1%), and SRs (64.2%) had fewer samples with acceptable bacterial levels. The geometric mean (GM) bacterial load in the ORs before aerosol-generating procedures (AGPs) was 116.8±1.8 CFU/m³, higher than after AGPs (58.9±2.1 CFU/m³). After controlling potentially confounding factors, the factors influencing bacterial loads occupied OR were temperature before AGPs (0.164 CFU/m3, 95%CI 0.017-0.311, p=0.029), the number of staff after AGPs (0.082 CFU/m3, 95%CI 0.019-0.144, p=0.011), and using saw/drill device after AGPs (0.701 CFU/m3, 95%CI -1.326-0.076, p=0.029). Predominant bacteria were Gram-positive cocci (90.8%), of which 20.5% were S. aureus. Most S. aureus (94.2%) were resistant to at least one drug, with 40.7% being multidrug-resistant. Additionally, 33.7% were methicillin-resistant S. aureus (MRSA). Conclusion: The indoor air of ORs and SRs may be a source of AMR bacteria, particularly MRSA, a concern for surgical site infections. Maintaining ventilation, cleanliness, and minimizing non-essential staff activities are crucial for reducing airborne pathogen transmission.