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Review

Microbiological Air Quality in Healthcare Environments: A Review of Selected Facilities

by
Katarzyna Kauch
1,
Ewa Brągoszewska
1,* and
Anna Mainka
2
1
Department of Technologies and Installations for Waste Management, Faculty of Energy and Environmental Engineering, Silesian University of Technology, 18 Konarskiego St., 44-100 Gliwice, Poland
2
Department of Air Protection, Faculty of Energy and Environmental Engineering, Silesian University of Technology, 22B Konarskiego St., 44-100 Gliwice, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(16), 8976; https://doi.org/10.3390/app15168976
Submission received: 21 July 2025 / Revised: 11 August 2025 / Accepted: 12 August 2025 / Published: 14 August 2025
(This article belongs to the Special Issue Selected Papers from the 12th International Conference of Environmental Protection and Energy)
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Abstract

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The findings of this review offer valuable insights into the microbiological air quality of healthcare environments, with practical implications for hospital administrators, infection control specialists, and policymakers. By identifying the most prevalent airborne microorganisms associated with healthcare-associated infections, along with their antibiotic resistance profiles, this study provides evidence for the development of more effective air quality management strategies.

Abstract

Exposure to microorganisms can significantly impact well-being and, more importantly, human health. A frequently overlooked aspect of indoor air quality (IAQ) research is the risk posed by harmful biological agents transported through the air in the form of biological aerosols. Given that healthcare facilities create environments with an increased risk of infection transmission, monitoring IAQ and reducing microbiological contamination have become global public health challenges. This paper presents a literature review, focusing on the current state of knowledge regarding microbiological air quality in healthcare settings. The analysis confirms that Escherichia coli and Staphylococcus aureus are among the most prevalent airborne pathogens in healthcare facilities. The review also underlines the necessity for harmonized guidelines and integrated air quality management strategies to reduce microbial contamination effectively. Finally, the review compiles data on microorganism concentration levels and influencing factors. The present study highlights that implementing standardized monitoring and effective air filtration and disinfection methods is essential to improving microbiological air quality and enhancing patient safety. The sources analyzed in this review were collected from databases such as PubMed, ScienceDirect, ResearchGate, and Web of Science, considering only English-language publications. The studies cited were conducted in multiple countries across different regions, providing a comprehensive global perspective on the issue.

1. Introduction

One of the key parameters determining indoor air quality (IAQ) is the concentration of pollutants. These pollutants comprise various categories, including biological contaminants, which may originate from both indoor and outdoor sources. Exposure to microorganisms such as fungi, bacteria, or viruses can significantly affect human well-being and, more importantly, health. Researchers often overlook, yet must address, the presence of harmful biological agents transmitted in the form of bioaerosols as a critical component of IAQ. Bioaerosols represent a crucial category of airborne agents that require special attention, especially in indoor environments. They consist of airborne particles composed of or derived from biological entities, typically ranging in size from a few nanometers to over 100 μm [1]. Bioaerosols include microorganisms such as bacteria, fungi, and viruses, as well as pollen, spores, and fragments of plant or animal origin [2]. Both natural and anthropogenic sources, such as vegetation, soil, water, human activity, and indoor environments, release these particles. Smaller particles can remain suspended in the air for extended periods and penetrate more deeply into the respiratory tract, which increases their potential to harm human health [3].
In healthcare settings, bioaerosols significantly contribute to the spread of infection. They play an essential role in transmitting healthcare-associated infections (HAIs), which present a significant challenge for healthcare systems [4,5,6]. HAIs develop as a result of a patient’s stay in a medical facility or medical procedures performed there, with symptoms typically appearing at least 48 h after admission [7]. Studies estimate that airborne bioaerosols cause approximately 10–20% of HAIs and hospital contamination [8]. These pathogens threaten the health of patients, healthcare workers, and visitors. Limited public awareness of biological contamination in indoor environments and potential transmission routes further exacerbates the problem [9].
Epidemiological data reflect the scale of the problem. The World Health Organization (WHO) reports that HAIs affect approximately one in ten patients worldwide, with higher rates in low- and middle-income countries. High-risk patient groups experience similar trends. The European Centre for Disease Prevention and Control (ECDC) reports that, on any given day, at least 1 in 15 hospitalized patients and 1 in 26 residents of long-term care facilities acquire HAI. Across Europe, HAIs occur in an estimated 8.9 million cases annually [4,5,7].
Not all microorganisms are pathogenic. Three principal parameters, i.e., species composition, concentration, and aerodynamic diameter, determine how bioaerosols affect human health. The aerodynamic diameter influences how deeply inhaled particles are deposited in specific regions of the respiratory system and how these particles interact with human cells [10,11,12].
Given that the unique environment of healthcare facilities elevates the risk of infection transmission, controlling IAQ and reducing microbiological contamination have emerged as global priorities in public health. Consequently, ensuring safe IAQ is now widely recognized as a critical worldwide challenge.
This paper presents a literature review on microbiological air quality in healthcare environments, with a focus on associated health risks, commonly used monitoring techniques, and identified research gaps. Sources were retrieved from PubMed, ScienceDirect, ResearchGate, and Web of Science, considering only publications in English from reputable scientific journals to ensure substantive quality and credibility. No strict publication date limits were applied; however, the reviewed studies spanned the years 2000–2025, with most originating from the last two decades.
Studies were selected based on predefined inclusion criteria to ensure methodological rigor and thematic relevance. These criteria encompassed publications in peer-reviewed and reputable scientific journals, direct relevance to the core research topic, geographic diversity of study locations, the use of active microbiological sampling techniques, and full-text availability in an accessible language. Keywords used for the literature search included “bioaerosols,” “airborne microorganisms,” “hospital,” “air quality,” “indoor air,” “healthcare facilities,” and “infections.” The detailed criteria are summarized in Table 1.
This methodological approach contributed to a coherent organization and interpretation of the reviewed literature. The consistent application of standardized methodologies in future studies, combined with larger datasets, may facilitate more robust comparisons and provide a basis for meta-analyses or causal inference. In line with these methods, the present review aimed to (1) synthesize current knowledge on microbiological air quality in healthcare environments; (2) evaluate associated health risks; (3) summarize monitoring approaches; and (4) identify gaps requiring further research and propose corresponding priorities.

2. Bioaerosols

Humans are the primary source of bioaerosols in indoor air [13,14,15]. During sneezing, coughing, and even speaking, microorganisms are released into the air, where they can remain suspended, settle on various surfaces, or be inhaled by individuals nearby [16]. Inhalation of polluted air has been shown to impair the respiratory system’s defense mechanisms, thereby increasing susceptibility to infections from airborne pathogens [17,18]. Consequently, in addition to exposure to contaminated indoor air, infection may also occur through contact with contaminated surfaces or direct interaction with an infected individual. The presence of bioaerosols in indoor air can lead to serious health concerns [19]. Studies have shown that the concentration of bacteria in ambient air can decrease when speaking because the human respiratory system can retain some of the bacteria and particles [20]. Airborne biological particles, depending on their size, can reach different regions of the respiratory system. However, special attention must be given to the respirable fraction, as particles with a diameter ranging from 1.1 to 3.3 μm penetrate the secondary and tertiary bronchi, while the smallest, not exceeding 1.1 μm, can reach the pulmonary bronchioles, which are the areas constituting the lower parts of the respiratory system (Figure 1) [10,21]. Such exposure promotes the development of serious diseases, including pneumonia and tuberculosis, due to the penetration of bacteria into the deeper parts of the respiratory tract. Furthermore, the presence of bacteria and fungi in the air can contribute to allergic and chronic conditions such as hay fever, asthma, sinusitis, conjunctivitis, and bronchitis [22,23].
In healthcare facilities, a significant number of individuals, including many patients with pre-existing infections, move through the premises daily. This dynamic environment increases the risk of infection transmission, making air quality control and the reduction of bioaerosols a key public health challenge.
A significant influence on the presence and concentration of biological aerosols in the hospital environment is exerted by external factors. While some studies do not indicate a correlation, the majority of studies in the literature suggest their considerable impact [25,26,27]. Among external factors, atmospheric conditions and seasonal variability are the most important. Changes in weather and the resulting alterations in air parameters directly influence contamination levels, as different microorganisms increase under distinct environmental conditions. Another significant factor is the facility’s location; urban areas often exhibit different types and concentrations of contaminants compared to greener, less industrialized regions. Finally, the age of the building also affects contamination levels, as advances in construction materials, building technologies, and the condition of ventilation systems over time have a direct impact on their operational efficiency [14,28,29]. Although atmospheric conditions and seasonal factors are frequently examined in scientific studies, the influence of a building’s structural characteristics is far less commonly considered. The properties of building materials, such as porosity and surface roughness, can promote the settlement of microorganisms and create favorable conditions for their growth. In the case of older buildings, analyzing the chemical composition of the materials used is also crucial, as they may influence the proliferation of microorganisms. Research indicates that the technical condition of healthcare facilities can significantly affect the frequency of hospital-acquired infections. Many facilities, particularly older ones, fail to meet current hygienic and technical standards for medical premises, thereby increasing the risk of microbiological contamination in the indoor environment [5,14,30,31].
Microorganisms present in the indoor air of hospital facilities are characterized by a different composition. In analyses concerning the morphological assessment of bacteria and fungi, individual species were identified in various hospital wards. The most common microorganism species associated with infections acquired in healthcare settings and identified in long-term care facilities are Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Clostridium difficile, as well as species of Enterococcus, Enterobacter, Klebsiella, and Candida [7,32,33,34]. Although not all healthcare-associated infections are transmitted via the airborne route, many of the pathogens listed in Table 2 have been identified in hospital air samples. This overview therefore provides an essential clinical context for understanding the potential implications of airborne microbiological contamination in healthcare environments. Bacteria are responsible for nearly 90% of HAIs, while infections caused by viruses, fungi, or mycobacteria are much less common [35,36].

3. Control and Reduction Strategies

The airborne transmission of microorganisms in indoor environments depends on several factors. Firstly, these include the duration of the agent’s activity—pathogenic microorganisms exhibit different survival capacities, which influence their persistence in the air and their potential to cause infection. The risk of infection increases when pathogens remain in the air for extended periods or at higher concentrations. Therefore, another critical factor is the duration of contact with the agent. A further key factor is the size of the particles. Depending on their size and weight, some can remain airborne for extended periods.
In contrast, others may settle on surfaces, which affects both the manner and duration of exposure to these microorganisms. Another consideration is the presence of additional pollutants, which can lead to an elevated concentration of microorganisms in the air. Polluted air can disrupt the respiratory microflora, which, in turn, increases the risk of infection [44]. Another highly significant consideration is the efficiency of methods for reducing airborne pathogens. The implementation of ventilation systems, air filtration, purification techniques, or disinfection processes plays a vital role in mitigating the risk of pathogen transmission [45,46]. Research is also being conducted on spatial planning and the allocation of healthcare resources to enhance access to medical care [47,48]. Such an approach may simultaneously mitigate the burden on healthcare systems and improve the management of air pollution-related issues.
Furthermore, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) outlines several strategies to effectively reduce microbiological contaminants in indoor environments. In addition to appropriate design requirements, ASHRAE emphasizes the role of increasing the air exchange rate to lower microbial loads. The use of airlocks is recommended to control airflow between adjacent rooms, while maintaining pressure differentials helps enforce directional airflow. Adjusting the temperature and humidity levels to the specific requirements of each space also prevents the development of conditions conducive to the growth of pathogens, while ensuring user comfort. Finally, zoning—using separate HVAC units—allows indoor air quality standards to be tailored to the needs of individual rooms [49].

3.1. Air Filtration

The most commonly used method for reducing contamination and minimizing the risk of pathogen transmission is air exchange through a ventilation system. However, this form of air circulation has certain limitations, particularly in terms of maintaining thermal comfort and ensuring adequate air distribution. An additional challenge arises from the specific nature of medical facilities. The ventilation system must be adapted to the specific tasks performed in individual rooms, while also considering the number and health status of people staying in these rooms [31]. HVAC air treatment systems are considered a more effective approach for controlling and reducing pollution. Their primary function is to regulate temperature, humidity, and air quality within the buildings they serve. In this context, filters are essential for ensuring the proper quality of indoor air in these systems. HEPA (high-efficiency particulate air) filters are the most widely used and are particularly recommended for controlling hospital-acquired infections. They remove 99.97% of particles with a diameter of ≥0.3 μm. ULPA (ultra-low penetration into air) filters, used in environments with the highest cleanliness requirements, achieve an efficiency of 99.9995% in removing particles with a diameter of ≥0.12 μm. However, due to the higher pressure drop that they generate compared with HEPA filters, their application is less common [50,51].
Several key factors, including airflow velocity, particle characteristics, and the properties of the filtration material, determine the efficiency of HEPA and ULPA filters. In general, filtration efficiency increases with greater particle size and, to a certain extent, with higher airflow velocity. It is important to emphasize that systems equipped with HEPA and ULPA filters require regular maintenance and frequent filter replacement. Cleaning these filters is generally not recommended, as it may compromise their performance. Furthermore, their service life can be reduced in environments with elevated temperatures or humidity levels [52].

3.2. Air Disinfection

An alternative to the mechanical removal of solid particles is air disinfection. However, to maximize the effectiveness of IAQ improvement, such techniques should be applied in combination with filtration. In the context of the risk of microbial growth on filter surfaces, this approach may also enhance the durability of HVAC system components [53]. Several methods used in healthcare facilities have been described in the literature, which differ in terms of effectiveness, application, and mechanism of action. Air disinfection methods are presented in Table 3. They can be applied directly to the surfaces of HVAC system filters to inhibit the growth of microorganisms and extend the life of the filters or applied directly in ventilation ducts or indoor spaces. Their specific application depends on the technology used and the hygiene requirements of the facility.
The methods presented in Table 3 are used to inactivate pathogens in the hospital environment. However, their effectiveness depends on certain factors, such as the type of microorganisms, environmental conditions, and technical parameters. In addition, their use is associated with significant limitations. UV radiation can pose a health risk to staff and patients if used improperly, and photocatalysis generates reactive oxygen species that can lead to secondary chemical pollution. These compounds, although effective in disinfection, can adversely affect air quality and human health, requiring further detailed research. In addition, the solutions described often encounter technical limitations due to the complexity of the installation design, as well as challenges related to effective system maintenance and associated costs, including high levels of energy consumption.
The combination of filtration systems with air disinfection methods effectively reduces the risk of infection. However, there are still no clearly defined parameters necessary for effective control of HAIs [50,53,59].

4. Formation of Microbial Contamination Levels

There is a lack of standardized guidelines for monitoring and assessing parameters related to IAQ, including microbiological analysis [19,60]. WHO experts recommend 1000 CFU/m3 as the permissible threshold for microorganism concentrations in indoor air. Alternative guidelines propose upper limits of 300 CFU/m3 for fungi and 750 CFU/m3 for bacteria. In turn, the Interdepartmental Commission for the Maximum Permissible Concentrations and Intensities of Health-Harmful Factors in the Work Environment suggested a threshold of less than 5000 CFU/m3 for both bacteria and fungi [61,62,63]. Therefore, the literature reviews in this field typically do not provide direct references to specific numerical values. Instead, studies primarily focus on the impact of internal and external factors. Table 4 and Table 5 present data on bacteria and fungi in healthcare facilities, specifying their concentration with the type of facility, ward, and season. Furthermore, this review examines the air sampling method, the presence of other pollutants, the number of occupants, the type of ventilation system, and the volume of analyzed space.
A review of the scientific literature revealed that the majority of available studies originated from Iran. Several potential explanations for this observation can be proposed. This trend may indicate a growing interest in the topic within that region, potentially linked to local socio-cultural factors, public health priorities, or the high level of research activity in Iranian academic institutions.
In contrast, locating relevant articles from countries such as the United States or Australia proved significantly more challenging. In the case of the United States, many of the available publications date to before the year 2000, which may suggest that academic interest in the subject was more pronounced in the past and has since declined. Possible explanations include a shift in research priorities over recent decades, a reduced relevance of the topic within the current public health landscape, or its broader integration into interdisciplinary research domains.
The reviewed studies assessing the concentrations of airborne bacteria and fungi in hospital environments exhibited several essential differences. Firstly, the investigations were conducted in a variety of hospital wards, often equipped with different types of ventilation systems. This variation may affect both the efficiency of air exchange and the removal of microbiological contaminants. In general, wards with modern filtration systems and positive air pressure should demonstrate lower levels of airborne microbial contamination compared to those with outdated or passive ventilation.
Moreover, the number of individuals present in the examined spaces, as well as the volume of the rooms, likely varied across the studies; however, in most cases, precise data on these parameters were not reported. This limitation can significantly hinder the direct comparability of results across studies, as occupant density influences the emission of microorganisms (originating from skin surfaces, clothing, and the respiratory tract). At the same time, room volume affects the degree to which airborne contaminants are diluted.
Another important factor differentiating the studies was the time of day and season during sample collection, as well as the geographical location of the facilities, corresponding to different climatic zones. These factors are critical to microbial dynamics because temperature, humidity, and sunlight exposure influence the survival, metabolic activity, and dispersal capacity of both bacteria and fungi. For example, increased humidity favors fungal growth, whereas bacteria may remain more active under moderate temperature conditions. Consequently, direct comparisons between data obtained in different seasons or climate zones are difficult without appropriate standardization. Nevertheless, the available data indicate a persistent risk of exposure for both patients and healthcare staff.
Low concentrations of microorganisms, such as those reported in a dental office in France (0–11 CFU/m3) [65] or during operations in Italy (13–82 CFU/500 L) [69] may indicate a high standard of sterility, adequate ventilation, and air filtration, which is crucial in rooms requiring special hygiene, such as operating rooms or intensive care units. The concentration of microorganisms in such environments may serve as an indicator of the effectiveness and regularity of cleaning procedures, including the application of appropriate disinfectants and the continuous monitoring of sanitary and hygienic conditions. High concentrations of microorganisms, such as those reported in a hospital in Thailand (880.19 CFU/m3) in female medicine [68] or in a women’s infectious disease ward in Iran (835 CFU/m3) [64] may suggest the need for more regular cleaning, as well as the need to improve ventilation or the air filtration system. Elevated values of CFU/m3 may also result from overcrowded conditions, which complicate air quality management efforts. Moreover, high concentrations, observed in an orthopedic ward at an Indian hospital (ranging from 3788 to 191,111 CFU/m3) [70], highlight the challenges of maintaining a controlled indoor environment in regions characterized by high temperature and humidity conditions that promote microbial proliferation. Comparable variability has also been documented in hospitals located in other areas. For instance, in the Korean hospital lobbies, the levels ranged from 50 to 2300 CFU/m3 [30], indicating potential difficulties in controlling both internal and external sources of contamination. Additionally, observed variability may result from emission sources, humans, and environmental conditions that favor their multiplication, or the ability to generate bioaerosols. Such fluctuations may reflect the influence of outdoor air pollution. Air inadequately filtered can significantly alter IAQ. Similar trends have been observed for fungal contamination.
Some studies suggest a correlation between air quality parameters and microorganism concentrations [27,67], while others have found no such association [67,68,75]. Additionally, increased movement within healthcare facilities and a higher number of visitors may contribute to elevated bioaerosol levels and facilitate their spread [27,75]. Furthermore, factors such as inadequate disinfection procedures, poor hygiene practices, improper use of personal protective equipment by staff, ineffective ventilation, external sources of microorganisms, and seasonal fluctuations have been identified as potential contributors to this phenomenon [70,75,76,77,78,79]. Other studies have reported that HEPA filters effectively reduce microbial load [80,81], whereas one did not confirm this effect [82]. Notably, in studies where strain identification was performed, the detected microorganisms almost invariably corresponded to those listed in Table 2. This finding confirms their widespread presence in hospital settings and underscores the importance of monitoring these specific pathogens as indicators in the assessment of microbiological air quality.
Due to the substantial heterogeneity of the available data and the absence of standardized measurement indicators, conducting a reliable statistical analysis was not feasible at this stage. Nevertheless, the authors recognize a clear need to strengthen the quantitative dimension in future research by incorporating empirical data obtained through direct measurements and analyses. Such efforts would enable the application of appropriate effect measures, facilitate methodological standardization, and enhance the comparability of results.
At the current stage of analysis, the causes of the discrepancies among individual study results cannot be determined, despite the selection of studies being based on specific criteria. These differences may arise from variations in geographical location and potential seasonal influences. The limited availability of information on other relevant parameters further constrains interpretation. The presence of such inconsistencies underscores the need for systematic, standardized investigations in this field. Conducting such research would facilitate causal inference and provide a valuable contribution to the existing body of knowledge.
The inability to interpret the results is a barrier to research in this field, posing a significant challenge to minimizing the risk of infections and ensuring a safe indoor environment for both medical staff and patients. This issue is particularly relevant in the context of antimicrobial resistance among airborne microorganisms, as the airborne-droplet route is considered one of the primary pathways for the spread of antibiotic-resistant pathogens.
Antibiotic resistance refers to the ability of bacteria to survive or multiply despite exposure to one or more antibiotics due to intrinsic or acquired resistance mechanisms. Acquired resistance is of particular concern, as it often leads to infections that are more difficult to treat, resulting in prolonged hospital stays and increased mortality rates [4,81,82,83].
A specific and more severe form of this problem is multidrug resistance (MDR), defined as resistance to at least three different classes of antibiotics. It is estimated that in some regions of the world, up to 75% of hospital-acquired infections are caused by MDR bacteria [84,85]. According to the European Antimicrobial Resistance Surveillance Network, MDR bacteria were responsible for over 800,000 infections in the European Union and European Economic Area (EU/EEA) in 2020 [86].
On a global scale, bacterial resistance to antimicrobial agents was estimated to have directly caused 1.14 million deaths in 2021 [87]. At the same time, the incidence of antibiotic-resistant bacteria continues to rise worldwide [88,89,90].

5. Conclusions

This review synthesizes current knowledge on microbiological air quality in healthcare environments, evaluates associated health risks, summarizes monitoring approaches, and identifies gaps requiring further research. According to the reviewed studies, bacterial concentrations ranged from below detection (<1 CFU/m3) to 191,111 CFU/m3 (in an orthopedic ward in a tropical hospital), with a median of approximately 300 CFU/m3 and a mean of 4729 CFU/m3. Fungal concentrations ranged from <1 CFU/m3 to 15,150 CFU/m3, with a median of 44.7 CFU/m3 and a mean of 514 CFU/m3. These findings address the first objective by demonstrating the substantial variability that occurs in microbial loads, which are affected by facility type, ventilation performance, environmental conditions, and infection control practices. The most frequently identified pathogens in hospital air included Staphylococcus aureus (associated with six infection types), Escherichia coli (five types), Enterobacter spp., and Klebsiella spp. (four types), Pseudomonas aeruginosa and Enterococcus spp. (three types), many of which are known for antibiotic resistance and significant airborne transmission potential.
In relation to the third objective, our synthesis confirms that active air sampling remains the most widely used method for detecting airborne microorganisms, with methodological diversity often limiting comparability between studies. The lack of harmonized sampling protocols, limited data on permissible indoor concentrations, and insufficient consideration of influencing factors such as room volume, occupancy, and other air quality parameters have emerged as major obstacles to robust monitoring.
Finally, we address the fourth objective to identify clear research and policy priorities. These include the development of standardized international guidelines for microbial air contamination, the expansion of research into underrepresented healthcare settings, such as hospices and long-term care facilities, and the implementation of longitudinal, multicenter studies that account for regional and seasonal variability. Achieving these goals will require integrated, multi-layered strategies combining architectural design, electrification of environmental controls, afforestation around facilities, and the application of effective air filtration and disinfection technologies.
Beyond technical measures, raising public and professional awareness of indoor air hygiene is essential. Even relatively simple interventions—such as limiting visitor numbers during outbreaks, ensuring correct use of personal protective equipment, and maintaining ventilation and filtration systems—can significantly reduce airborne infection risks. By directly aligning these findings and recommendations with the stated objectives, this review provides both a comprehensive knowledge base and a practical framework for improving microbial air quality in healthcare environments.

Author Contributions

Conceptualization, K.K., E.B. and A.M.; writing—original draft preparation, K.K.; writing—review and editing, E.B. and A.M.; supervision, E.B. and A.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Faculty of Energy and Environmental Engineering, Silesian University of Technology through a statutory research grant for young scientists (BKM 585/RIE2/2025, 08/020/BKM25/0048).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
IAQIndoor air quality
HAIHealthcare-associated infections
WHOWorld Health Organization
EDCDThe European Center for Disease Prevention and Control
ASHAREAmerican Society of Heating, Refrigerating, and Air-Conditioning Engineers
HVACHeating, ventilation, and air conditioning
HEPAHigh-efficiency particulate air
ULPAUltra-low penetration air
UV Ultraviolet radiation
CFUColony forming unit
N/ANot applicable
MDRMultidrug-resistant bacteria
EU/EEAEuropean Union and European Economic Area

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Applsci 15 08976 g001
Figure 1. Regions of respiratory system with particle size settling at specific depths. Based on [24].
Figure 1. Regions of respiratory system with particle size settling at specific depths. Based on [24].
Applsci 15 08976 g001
Table 1. Criteria for article selection.
Table 1. Criteria for article selection.
No.Criterion
1.Publication in peer-reviewed and reputable scientific journals
2.Relevance to the core research topic
3.Inclusion of studies from geographically diverse locations
4.Application of active microbiological sampling techniques
5.Availability of the full text in an accessible language (e.g., English)
Table 2. Distribution of healthcare-associated infections (HAIs) in European hospitals and the most frequently identified microorganisms responsible for these infections [7,27,31,33,36,37,38,39,40,41,42,43].
Table 2. Distribution of healthcare-associated infections (HAIs) in European hospitals and the most frequently identified microorganisms responsible for these infections [7,27,31,33,36,37,38,39,40,41,42,43].
Infection TypeRelative Frequency of Occurrence During the Patient’s Hospital StayGenus/Species
Pneumonia, lower respiratory tract infection31%Aspergillus spp.,
Enterobacter spp.,
Escherichia coli,
Klebsiella spp.,
Staphylococcus aureus
Urinary tract infection20%Enterococcus spp.,
Escherichia coli,
Klebsiella spp.,
Pseudomonas aeruginosa,
Staphylococcus aureus
Surgical site infection12%Enterococcus spp.,
Pseudomonas aeruginosa,
Staphylococcus aureus
Bloodstream infection13%Enterobacter spp.,
Enterococcus spp.,
Escherichia coli,
Klebsiella spp.,
Staphylococcus aureus
Gastrointestinal infections9%Clostridium difficile,
Enterobacter spp.
Escherichia coli,
Klebsiella spp.,
Staphylococcus aureus
Systemic infections5%Aspergillus spp.,
Escherichia coli
Skin/soft tissue infections4%Enterobacter spp.,
Pseudomonas aeruginosa,
Staphylococcus aureus
Unspecified5%-
Table 3. Selected methods of indoor air disinfection.
Table 3. Selected methods of indoor air disinfection.
MethodMechanismOverviewRefs.
Ultraviolet germicidal irradiationDamage to the nucleic acids of microorganisms and inhibition of further replication of pathogens.Effectiveness depends on wavelength, microbe type, and exposure time.[31,54,55]
Photocatalytic oxidationGeneration of reactive oxygen species and destruction of cell walls or viral capsids.Radical reactions can create secondary pollutants harmful to health, air quality, and human health.[51,56,57]
Plasma disinfectionDamage to enzymes and structural proteins in microorganisms, disruption of metabolism, and inactivation.Reactions may release water vapor, potentially raising ozone (O3) levels—effects on health and air quality are not well understood.[51,58]
Table 4. A review of bacterial air quality in healthcare environments.
Table 4. A review of bacterial air quality in healthcare environments.
Selected Hospital FacilitiesUnit AreaBioaerosol ConcentrationsRef.
Bacteria
Educational and Medical Hospital; Tabriz, IranWomen’s infectious
disease ward		835 CFU/m3
(highest value)		[64]
Men’s infectious
disease ward		119 CFU/m3
(lowest value)
Hospital; Warsaw, PolandHealth emergency
department		130–4200 CFU/m3
(range)
470 CFU/m3
(mean value)		[63]
Ambulance130–1400 CFU/m3
(range)
300 CFU/m3
(mean value)
Private healthcare facilities; Nancy and Rennes, FranceDental office0–11 CFU/m3
(range)		[65]
Pharmacies40–680 CFU/m3
(range)
University Clinical Centre; Banja Luka, Bosnia and HerzegovinaAll the examined wards30–6295 CFU/m3
(range)		[66]
University Hospital; GreeceInternal medicine ward689 CFU/m3
(mean value)		[67]
Surgical ward596 CFU/m3
(mean value)
Neonatal unit509 CFU/m3
(mean value)
Intensive care unit353 CFU/m3
(mean value)
Hospital; ThailandMale surgery533.81 CFU/m3
(mean value)		[68]
Female surgery550.15 CFU/m3
(mean value)
Male medicine577 CFU/m3
(mean value)
Female medicine880.19 CFU/m3
(mean value)
Municipal Hospital; Setúbal, PortugalEmergency service240–736 CFU/m3
(range)		[29]
Surgical ward99–495 CFU/m3
(range)
Operating theater12–170 CFU/m3
(range)
Community hospital; Modena, ItalyDuring operations 13–82 CFU/500 L
(range)		[69]
Hospital; Chennai, IndiaOrthopedic department3788–191,111 CFU/m3
(range)		[70]
Hospitals; KoreaHospital lobbies
(at 6 hospitals)		50–2300 CFU/m3
(range)
720 CFU/m3
(mean value)		[30]
Private hospital; Goiânia/GO, BrazilPost-surgical rest room566 CFU/m3[71]
Operating room theater124.5 CFU/m3
Hospital; Murcia, SpainOperating theaters1.67–157 CFU/m3
(range)		[72]
Hospital rooms4.12–1293 CFU/m3
(range)
Maternity wards14.33–224 CFU/m3
(range)
Specialty hospital; Midwestern U.S.Cardiac intensive care unitN/A[73]
Organ transplant unit
AIDS unit
Bone marrow transplant unit
Two hospitals;
Canada		Bronchoscopy room,
hospital 1		43–208 CFU/m3
(range)		[74]
Bronchoscopy room,
hospital 2		40–370 CFU/m3
(range)
N/A—not applicable.
Table 5. A review of fungal air quality in healthcare environments.
Table 5. A review of fungal air quality in healthcare environments.
Selected Hospital FacilitiesUnit AreaBioaerosol ConcentrationsRef.
Fungi
Educational and Medical Hospital; Tabriz, IranBurn surgery unit and men’s infectious disease ward49 CFU/m3
(highest value)		[64]
Pediatric burn unit28 CFU/m3
(lowest value)
Hospital; Warsaw, PolandHealth emergency
department		3.4–81 CFU/m3
(range)
67 CFU/m3
(mean value)		[63]
Ambulance6.7–650 CFU/m3
(range)
67 CFU/m3
(mean value)
Private healthcare facilities; Nancy and Rennes, FranceDental office0–240 CFU/m3
(range)		[65]
Pharmacies2–150 CFU/m3
(range)
University Clinical Centre; Banja Luka, Bosnia and HerzegovinaAll the examined wards20–1125 CFU/m3
(range)		[66]
University Hospital; GreeceInternal medicine wardN/A[67]
Surgical ward
Neonatal unit
Intensive care unit
Hospital; ThailandMale surgery351.19 CFU/m3
(mean value)		[68]
Female surgery261.36 CFU/m3
(mean value)
Male medicine264.67 CFU/m3
(mean value)
Female medicine318.70 CFU/m3
(mean value)
Municipal Hospital; Setúbal, PortugalEmergency service27–933 CFU/m3
(range)		[29]
Surgical ward1–32 CFU/m3
(range)
Operating theater<1 CFU/m3
(range)
Community hospital; Modena, ItalyDuring operationsN/A[69]
Hospital; Chennai, IndiaOrthopedic department0–15,150 CFU/m3
(range)		[70]
Six hospitals; KoreaHospital lobbies
(at 6 hospitals)		11–2200 CFU/m3
(range)
77 CFU/m3
(mean value)		[30]
Private hospital; Goiânia/GO, BrazilPost-surgical rest roomN/A[71]
Operating room theater
Hospital; Murcia, SpainOperating theaters0–7.33 CFU/m3
(range)		[72]
Hospital rooms0–266 CFU/m3
(range)
Maternity wards0.44–44.67 CFU/m3
(range)
Specialty hospital; Midwestern U.S.Cardiac intensive care unit0–360 CFU/m3
(range)
54.9 CFU/m3
(mean value)		[73]
Organ transplant unit2–680 CFU/m3
(range)
83.5 CFU/m3
(mean value)
AIDS unit0–198 CFU/m3
(range)
41.7 CFU/m3
(mean value)
Bone marrow transplant unit0–260 CFU/m3
(range)
41 CFU/m3
(mean value)
Two hospitals; CanadaBronchoscopy room,
hospital 1		N/A[74]
Bronchoscopy room,
hospital 2
N/A—not applicable.
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Kauch, K.; Brągoszewska, E.; Mainka, A. Microbiological Air Quality in Healthcare Environments: A Review of Selected Facilities. Appl. Sci. 2025, 15, 8976. https://doi.org/10.3390/app15168976

AMA Style

Kauch K, Brągoszewska E, Mainka A. Microbiological Air Quality in Healthcare Environments: A Review of Selected Facilities. Applied Sciences. 2025; 15(16):8976. https://doi.org/10.3390/app15168976

Chicago/Turabian Style

Kauch, Katarzyna, Ewa Brągoszewska, and Anna Mainka. 2025. "Microbiological Air Quality in Healthcare Environments: A Review of Selected Facilities" Applied Sciences 15, no. 16: 8976. https://doi.org/10.3390/app15168976

APA Style

Kauch, K., Brągoszewska, E., & Mainka, A. (2025). Microbiological Air Quality in Healthcare Environments: A Review of Selected Facilities. Applied Sciences, 15(16), 8976. https://doi.org/10.3390/app15168976

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