en Environmental microbiology Original articles <div style="text-align: justify;"><span style="font-size:11pt"><span style="line-height:115%"><span style="text-autospace:none"><span style="font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;"><b><i><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;">Introduction:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;"> Given that hospital air is one of the important environmental sources for transmission of microorganisms, the importance of airborne transmission in the epidemiology of hospital-acquired infections (HAIs) has gained attention in the past two decades. Therefore, the present study aims to determine the concentration of bacteria in association with airborne particulate matter (PM) in the outdoor and indoor air of two hospital wards. </span></span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:115%"><span style="text-autospace:none"><span style="font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;"><b><i><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;">Materials and methods:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;"> The GRIMM 1.109 dust monitor and the Andersen one-stage viable impactor were used for particle counting and bioaerosol sampling, respectively. </span></span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:115%"><span style="text-autospace:none"><span style="font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;"><b><i><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;">Results:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;"> The average levels of airborne bacteria sampled from outdoor air were 33 colony-forming units (CFU/m³), and in the air samples of medical and infectious disease wards, they were 76 and 85 CFU/m³, respectively. <i>Staphylococcus</i> spp. and <i>Acinetobacter</i> spp. were the most prevalent bacteria in the samples. Statistical analysis showed a significant association between PM_2.5, and PM₁₀ particle mass concentrations and airborne bacteria concentrations in indoor air samples (P-value </span></span></span><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;">< 0.05</span></span></span><span style="font-size:10.0pt"><span style="line-height:115%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;">). </span></span></span></span></span></span></span><br> <b><i><span style="font-size:10.0pt"><span style="line-height:107%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;">Conclusion:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:107%"><span style="font-family:&quot;Times New Roman&quot;,&quot;serif&quot;"> Some bacterial agents of HAIs existed in hospital air and may be problematic for immunocompromised patients. Higher levels of bacteria in indoor air compared to outdoor air may indicate that the bacteria were of indoor origin, such as the presence and activities of people. Moreover, the results showed that particle counting may be a useful tool for airborne bacteria monitoring.</span></span></span></div> Aerosols, Bacteria, Particulate Matter, Hospitals. 2125 2133 http://jehsd.ssu.ac.ir/browse.php?a_code=A-10-701-1&slc_lang=en&sid=1 Fatemeh Atoof atoof@kaums.ac.ir 0000-0002-1103-7461 No Department of Biostatistics and Epidemiology, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Sahar Gholipour sahar.gholipour71@gmail.com 0000-0003-3265-0932 No Department of Environmental Health Engineering, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Zahra Shamsizadeh z_shamsizadeh69@yahoo.com 0000-0002-3055-2995 No Department of Environmental Health Engineering, School of Health, Larestan University of Medical Sciences, Larestan, Iran. Mohsen Amirimoghaddam Amiri@gmail.com 0000-0003-4304-0558 No Department of Biostatistics and Epidemiology, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Nezam Mirzaei nezammirzaei@yahoo.com 0000-0003-4779-1519 Yes Department of Environmental Health Engineering, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Ali Nazari-Alam nazarialam.ali@gmail.com 0000-0003-4770-5836 No Department of Microbiology and Immunology, Faculty of Medicine, Kashan University of Medical Sciences, Kashan, Iran. Davarkhah Rabbani davarrabbani@gmail.com 0000-0001-5612-9880 No Department of Biostatistics and Epidemiology, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Mansour Baziar baziar@gmail.com 0000-0001-5005-6537 No Ferdows school of Paramedical and Health, Birjand University of Medical Sciences, Birjand, Iran. Gholamreza Hoseindoost Hosseindoust@gmail.com 0000-0002-5148-5779 No Department of Biostatistics and Epidemiology, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Gholamreza Mostafaii Mostafaii@kaums.ac.ir 0000-0002-7088-0133 No Department of Biostatistics and Epidemiology, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran. Abbas Bahrami Bahrami@kaums.ac.ir 0000-0001-9016-8998 No Department of Occupational Health Engineering, Faculty of Health, Kashan University of Medical Sciences, Kashan, Iran.