Spatiotemporal variations , human occupancy, and ventilation systems as modulators of airborne bacterial communities in two medical centers in Temuco city (southern Chile)

In indoor environments, the United States Environmental Protection Agency (US-EPA) and indoor air quality (IAQ) regulations in Europe and Asia have established concentration and exposure thresholds for air contaminants, primarily chemical compounds, which can be found at levels 2 to 5 times higher than in outdoor environments. However, bioaerosols and the air microbiome, composed significantly of microorganisms (bacteria and fungi), have been inadequately addressed or excluded from these IAQ regulations . Studies on the biological risks of indoor airborne bacteria have commonly established an association with the type and/or activity of each indoor environment (e.g., medical, residential, or industrial). Medical centers (MCs) are considered complex environments with high biological risk due to the presence of airborne human pathogenic bacteria (PAHPB), which are particularly relevant for immunocompromised patients. Human occupancy (HO) is one of the main modulators of indoor airborne bacterial communities, as patients and staff in MCs can contribute to the dispersal of these bacteria through activities such as breathing, coughing, and cleaning. The ventilation system (VS), whether mechanical or non-mechanical (e.g., open doors and windows), also strongly influences the indoor bacterial community. Environmental factors such as temperature and humidity are important determinants for the dispersion and survival of bacteria in these environments. Although bacterial communities in MCs are diverse, most bioaerosol studies have focused on PAHPB due to their clinical relevance as agents of nosocomial infections. Additionally, MCs are considered critical points for the occurrence and emission of antibiotic-resistant bacteria (ARB), raising concerns about the possible horizontal transfer of antibiotic resistance genes (ARGs) between air and patient microbiomes. The city of Temuco, in southern Chile, is one of the most air-polluted cities in South America, especially during the colder months. An air quality program has been implemented in the city, although it exclusively focuses on outdoor environments, with no data on the indoor air microbiome. This study investigated the spatiotemporal variations in the composition and abundance of indoor airborne bacteria, as well as the occurrence of PAHPB and ARGs, in bioaerosol samples collected from patient waiting rooms in two MCs in Temuco between 2021 and 2022. Additionally, the potential influence of HO and VS as modulators of these environments was evaluated.