Indoor air quality and airborne transmission under the One Health lens: A scoping review

Abstract

Humans spend around 90 % of their time indoors, making Indoor Air Quality (IAQ) of utmost importance. Its importance has been recently highlighted by COVID-19. However, IAQ significantly impacts public health, concerning not only respiratory, but also cardiovascular diseases. The World Health Organization defines One Health as “an approach to designing and implementing programmes, policies, legislation and research in which multiple sectors communicate and work together to achieve better public health outcomes”. This scoping review fills a gap in the literature by exploring the One Health approach, which integrates human, animal, and environmental health, applied to the study of airborne transmission.

We searched various databases for articles that assessed microbiological IAQ using the One Health approach. Eligible documents assessed air contamination, with a focus on infectious threats and antimicrobial resistance. Our work maps the topics covered, the methodologies employed, and the evidence gaps identified.

Our literature search yielded 8471 articles, from which 18 studies were selected for detailed analysis. Findings indicate that the One Health approach effectively addresses the complex challenge of airborne microbiological contamination. This approach comprises a comprehensive view of topics, contexts, agents and methodologies employed to study airborne transmission in indoor spaces. The agents included range from influenza, legionella and others, to the dispersal of mycotoxins and antibiotic resistance genes. The role of animals in diverse human–animal interaction settings was highlighted as a significant factor influencing IAQ, particularly in relation to zoonotic spillover risks, and the airborne transmission of antimicrobial resistance.

The review also identified evidence gaps in research and highlighted the need for interdisciplinary collaboration.

Incorporating One Health principles into IAQ research is essential for developing comprehensive health strategies that can address both current and emerging infectious threats. Future research should prioritise settings involving animal-human indoor interactions, focusing on workplace contamination, zoonotic spillover, emergent threats, and the airborne transmission of antimicrobial resistance, to ensure a robust framework for safeguarding global health.

Highlights

• •One Health approach should be applied to IAQ studies and infection risk as we spend 90 % of our time indoors.
• •We identified studies on atmosphere, zoonosis, AMR, emergent threats and occupational risks.
• •Methods used in these studies include epidemiologic, cross sectional and longitudinal designs.
• •Occupational risks, zoonosis, emerging agents, and dispersal of AMR were evidence gaps identified.

1. Introduction

The COVID-19 pandemic emerged in a so-called “post-infectious disease era” [1]. Like every other global event, it urged us to rethink how we currently live and think, especially in relation with our surroundings. The pandemic also dramatically challenged the prevailing focus on Human Health centred on chronic, non-communicable diseases. The emphasis on preventing and protecting the population from SARS-CoV-2 transmission led to a substantial evolution of knowledge regarding the transmission modes, underscoring the importance of air quality and the airborne route [[2], [3], [4]].

Although seemingly comprehensive, our previous vision of the world and human health is now increasingly seen as incomplete. The pandemic highlighted that Human Health is interconnected across communities, continents, and the globe, encompassing all biological existence and the environment, reflecting the principles of One Health [[5], [6], [7]]. According to the World Health Organization (WHO) “One Health’ is an integrated, unifying approach to balance and optimize the health of people, animals and the environment” [8].

The One Health approach is a comprehensive framework for integrating human health with the environment, and with plants and non-human animal health, through a cross-sectoral interplay and interdependence. The post-pandemic era is an opportunity to strengthen One Health security sustainability through access to clean air and fresh water, medicines and the promotion of healthy and sustainable diets, while ensuring food safety. The emphasis must be on preventing and promoting more equitable systems, environments, economies, and societies [9,10].

In the aftermath of COVID-19 pandemic, which resulted in the loss of millions of lives and had a tremendous impact on individuals, families, societies, and global economics, interdependence and interspecies relationships have gained increased importance. The emergence of the SARS-CoV-2 virus, a zoonotic agent that became easily transmissible among humans, has highlighted and reinforced the need for a One Health approach, considering Human Health within its connection with ecosystems and the environment. The One Health perspective considers the interdependence of species and fosters close collaboration among different scientific disciplines such as veterinary medicine, agriculture, biomedicine and Public Health. It includes various issues such as antimicrobial resistance (AMR), zoonoses, airborne transmission, vector-borne diseases, food safety and foodborne diseases, environmental health, and climate change [7,8,[10], [11], [12]].

The importance of the One Health Perspective is underscored by the fact that almost three-quarters of the emerging infectious diseases over the last three decades have been of animal origin, according to the One Health Commission [13]. When focusing on “Human Health and its surroundings”, it is essential to consider the breathable air, to which we are continuously exposed. Each year, the death toll attributable to the inhalation of airborne contaminants exceeds 13 million people [14] At “The Science behind One Health”, the International Conference on One Medicine One Science (iCOMOS), air pollution attributable health problems were the second major thematic, considering that the health of all living creatures that breathe is inextricably linked to the composition and quality of the air.

We spend 90 % of our time indoors, making the indoor environment the primary source of exposure to air contaminants, including indoor pollutants and infectious agents, present at higher concentrations than outdoors [15,16]. Indoor air quality (IAQ) has been associated with multiple respiratory and cardiovascular diseases, diabetes and mental illnesses such as depression and dementia [17]. Of particular relevance, in the context of One Health, diverse indoor environments are shared not only by humans but also by animals, such as in households, veterinary settings or breeding farms, for example. This shared environment predisposes both humans and animals to airborne exposure pathways, highlighting the relevance of a One Health perspective when addressing IAQ-related health risks [[18], [19], [20], [21]].

According to the WHO, household air pollution was responsible for approximately 3.2 million deaths in 2020, including over 237,000 deaths of children under the age of five. Of the 3.2 million deaths, 32 % were due to ischemic heart disease, 22 % to stroke, and 21 % to respiratory infections, which account for 44 % of all pneumonia deaths in children under five years old and 22 % of those in adults. Additionally, 19 % were from chronic obstructive pulmonary disease (COPD), and 6 % were from lung cancer [22].

IAQ is also dependent on outdoor air quality and can therefore be affected by climate change due to heat and mass transfers, although the influence of climate change is poorly understood. [23] The impact of IAQ on health depends not only on the chemical and physical properties of the particles but also on the transportation of infectious agents [24].

Biological material can be dispersed across a vast environmental area, covering many kilometres, in the form of bioaerosols, which are airborne particles containing biological material, including both living and dead microorganisms [25]. Indoor pollutant levels are driven by three classes of factors: a) properties of pollutants b) building factors, such as ventilation rates; and c) occupant behavior. Indoor pollutants reflect the sum of contributions from exterior and interior sources [26]. Therefore, ventilation is an important strategy to improve IAQ. The WHO further stimulates the use of more efficient ventilated stoves as an important health intervention in low- and middle-income countries (LMICs) [27]. Additionally, the transmission of airborne pathogens and other deleterious particles, which can lead to respiratory or other diseases, can be prevented by using personal protection measures, such as masks, hand hygiene, social distancing, and implementing decontamination and disinfection procedures [28].

Natural ventilation is major determinant of IAQ, which can be achieved by infrastructure designed to promote fresh air flow, and by simply opening doors and windows. Nevertheless, it is not as effective as other mechanical solutions, and the installation of ultraviolet air disinfection systems, filters and air purifiers is recommended. However, despite the effectiveness of air purification systems and mechanical ventilation using HVAC (heating, ventilation, and air conditioning) systems, they tend to be costly and require regular maintenance [[29], [30], [31]].

In addition to pollutants and infectious agents, evidence on human toxicity from inhaled fungal toxins, or dispersal of AMR, for example, is scarce [16,32]. The aerial movement of AMR is closely interconnected with human health, easily dispersing throughout the environment and penetrating the human respiratory pathways [32,33]. The deposition of Particulate Matter (PM) in the respiratory tract depends upon the size of the particles: particles larger than PM₁₀ are typically deposited in the upper respiratory tract, while fine particles, PM_2.5, reach the lower respiratory tract. Ultrafine particles smaller than 0.1 μm penetrate deeply into the alveoli [34].

Multiple methodologies are currently used to measure indoor bioaerosol exposure and assess health risks. As a comprehensive framework, the One Health approach can be applied to the full cycle of prevention control, thus contributing to global health security - from prevention to early detection, integrating preparedness, response and management [9].

This study assessed the extent of literature on One Health when applied to IAQ, specifically regarding microbiologic parameters, in light of the COVID-19 pandemic. A broad main research question was formulated:

What are the current designs, topics addressed, and methodologies employed in studies on air quality under the One Health approach?

Four directed sub-questions guided the scoping review:

• •What is the current contribution of the One Health approach to IAQ and infection control?
• •What are the current research designs and methods used in a One Health approach for IAQ studies?
• •What opportunities for contribution and evidence gaps can be addressed by the One Health approach in IAQ and infection control research?
• •Did COVID-19 impact the One Health approach to IAQ?

2. Methods

This scoping review was conducted in accordance with the Joanna Briggs Institute (JBI) methodology for scoping reviews and followed the recommendations outlined in the PRISMA Extension for Scoping Reviews (PRISMA-ScR). The quality of the methodologies used in each study was not assessed, as per the guidelines for scoping reviews [[38], [39], [40]]. A preliminary search of Web of Science, MEDLINE, the Cochrane Database of Systematic Reviews, JBI Evidence Synthesis and PROSPERO was conducted, and no current or underway systematic reviews or scoping reviews on the topic were identified. The main objective of this scoping review was to examine how research on microbiological IAQ is conducted from a One Health perspective, with particular attention to research methods and the subjects and topics covered by investigation.

2.1. Search strategy and selection criteria

We developed a search strategy, which was conducted between July and August 2023. The first phase of the review involved a literature search to identify the keywords and filters that were used to construct the search queries. The keywords used in this review are listed in Supplementary material.

Multiple databases were used to search for literature, including Web Of Science, PubMed, Scopus, and EBSCO. The search on the topic included the text words contained in the titles, abstract and indexed terms (see supplementary table). The search strategy was adapted according to the database/source. A combination of filters was used to construct search terms in a way that was accurate and not overly restrictive. Given the recent nature of the One Health approach concept and the intent to explore the impact of the pandemic, the search did not limit the date of publications. The review included studies published in English, Portuguese and Spanish.

2.2. Study/source of evidence selection

All identified citations were compiled and uploaded into Rayyan and duplicates were removed [41]. Following a pilot test, two independent reviewers identified potentially relevant citations by title. A re-screening of the previously selected citations was then undertaken, including abstracts and findings. The latter selection was then scanned to confirm suitability for the aims and purposes of this review. All discordances were resolved through discussion or with additional review by the most experienced members of the team.

The papers included in the scoping review were further analysed for data extraction using a data extraction sheet developed by the reviewers, provided in the Supplementary Material.

Data extracted from selected studies were collated and presented in Supplementary material. Specific information retrieved includes an overview of the One Health topics addressed, location, sampling and methodologies used, as well as evidence gaps identified by the article. A total of 18 papers were reviewed. Data regarding One Health topics, location are presented in Table 2. Participants, sampling and laboratory analyses are subsequently presented in Table 3. Evidence gaps identified in the studies are presented in Table 4.

Table 2.

Articles analysed in the Scoping Review.

Title	Author	year	Topic - Threats	Location
1.Microbial contamination in grocery stores from Portugal and Spain ‚The neglected indoor environment to be tackled in the scope of the One Health approach	Viegas et al	2023	Environmental contamination; ocupational exposure; Food Safety	Portugal + Spain
2.Probable Transmission of SARS-CoV-2 from African Lion to Zoo Employees, Indiana, USA, 2021	Siegrist, A, et al	2023	Emerging diseases (Covid-19); zoonotic transmission	Indiana, USA
3.A Risk Factor Analysis of SARS-CoV-2 Infection in Animals in COVID-19-Affected Households	Kuhlmeier, E et al	2023	Emerging diseases (Covid-19); zoonotic transmission	Zurich, Switzerland
4.Antibiotic Resistance Genes in Aerosols: Baseline from Kuwait	Habibi, N et al	2023	Antimicrobial Resistance; environmental contamination (dissemination of ARGs)	Kuwait
5.Legionella spp. in Thermal Facilities: A Public Health Issue in the One Health Vision	Laganà, P et al	2023	Environmental Contamination; ocupational exposure	Messina (Italy)
6.Unveiling the Occupational Exposure to Microbial Contamination in Conservation–Restoration Settings	Viegas et al	2022	Environmental Contamination; ocupational exposure	Lisbon, Portugal
7.Antimicrobial Resistance in the Environment: Towards Elucidating the Roles of Bioaerosols in Transmission and Detection of Antibacterial Resistance Genes	George, Paul B.L et al	2022	Antimicrobial Resistance; environmental contamination (dissemination of ARGs)	Northern Canada, France
8.Revealing the distribution characteristics of antibiotic resistance genes and bacterial communities in animal-aerosol-human in a chicken farm: From One-Health perspective	Yang, F et al	2021	Antimicrobial Resistance; environmental contamination; occupational exposure	Jiaozuo, China
9.Evaluation of potential risk of transmission of avian influenza A viruses at live bird markets in response to unusual crow die-offs in Bangladesh	Rahman, M et al	2020	Environmental Contamination; ocupational exposure; zoonotic infections	Bangladesh
10.Impact of microbial air quality in preschools on paediatric respiratory health	Madamarandawala, P et al	2019	Environmental Contamination; ocupational exposure; zoonotic infections	Central Province, Sri Lanka
11.Bioaerosol sampling at a live animal market in kunshan, china: A noninvasive approach for detecting emergent viruses	Wang, X et al	2020	Environmental Contamination; ocupational exposure; zoonotic infections	Kunshan City, China
12.Evidence for cross-species influenza a virus transmission within swine farms, china: A one health, prospective cohort study	Ma, M et al	2018	Environmental Contamination; ocupational exposure; zoonotic infections	China
13.Inhalable antibiotic resistomes emitted from hospitals: metagenomic insights into bacterial hosts, clinical relevance, and environmental risks	Wu, D et al	2022	Antimicrobial Resistance; environmental contamination (dissemination of ARGs)	Guangzhou, China
14.Management following the first confirmed case of SARS-CoV-2 in a domestic cat associated with a massive outbreak in South Korea	Han, T, et al	2021	Emerging diseases (Covid-19); zoonotic transmission	South Korea
15.Influence of pig farming on human Gut Microbiota: role of airborne microbial communities	Moor, J et al	2021	Environmental Contamination; ocupational exposure; zoonotic infections	Swiss cantons (Vaud, Bern, Fribourg, Jura)
16.Bioaerosol sampling in modern agriculture: A novel approach for emerging pathogen surveillance?	Anderson, B et al	2016	Environmental Contamination; Emerging diseases	Zhongshan, China,
17.A cross-sectional study of avian influenza A virus in Myanmar live bird markets: Detection of a newly introduced H9N2?	Borkenhagen, L et al	2023	Environmental Contamination; ocupational exposure; zoonotic infections	Myanmar
18.Spread of Sporothrix spp. through respiratory droplets from infected cats: A potential route of transmission	De Andrade, F et al	2022	Zoonotic transmission	Brazil

Table 3.

Methodology - articles analysed in the Scoping Review.

Author	year	Setting	Species	Agent	Sampling (sample and/or sampler)	Laboratory	Sampling period/duration
Viegas et al	2023	Grocery stores	NA	Mycotoxin; fungi, bacteria	passive sampling: (Electrostatic Dust Cloths — EDC) and surface swabs)	Culture-based Methods (Bacteria and Fungi) and Fungal idenfication. Fungal resistant profile: Molecular tools (qPCR) (Target fungal species Cytotoxicity + Mycotoxins)	30 days
Siegrist, A, et al	2023	Zoo	1 lion; 9 humans	SARS-CoV-2	nasopharyngeal swab samples (no air samples)	Epidemiologic study. Reverse transcription PCR (RT-PCR) or rapid antigen test for diagnostic confirmation	NA
Kuhlmeier, E et al	2023	household	172 cats, 49 dogs, 2 horses,2rabbits, 1hamster	SARS-CoV-2	122 COVID-19-affected households (336 humans; 226 animals) (no air samples)	RT-qPCR for diagnostic confirmation. An in-house-developed enzyme-linked immunosorbent assay (ELISA) was used to detect SARS-CoV-2.
Habibi, N et al	2023	outdoor + indoor air from 3 hospitals	NA	Bacteria	customized device: a sampler pumped air at the rate of 30 L min − 1	Total bacterial counts estimated through quantitative polymerase chain reaction (qPCR). Microbial DNA qPCR assays for the detection of ARGs or HT-qPCR analysis through the SmartChip qPCR assay	weekly for 360 min; 6 months
Laganà, P et al	2023	Thermal facilities	NA	Legionella	water and vapour samples from thermal facilities	Culture plates and subsequent latex micro-agglutination test kit with polyvalent antisera.	From 2004 to 2019
Viegas et al	2022	restoration studios	15 workers	Mycotoxin; fungi, bacteria	Deposition samples: Electrostatic Dust Cloths;	Culture-based Methods (Bacteria and Fungi) and Fungal idenfication. Fungal resistant profile: Molecular tools (qPCR) (Target fungal species Cytotoxicity + Mycotoxins)	30 days
George, Paul B.L et al	2022	Vehicle filters, hospitals, wastewater; Aquatic; animal farms, in vitro, animal models, conifer needles, clouds, rain	NA		Filtration; electret filter, passive sampling, liquid samplers (cyclone, impactation), large volume concentrators and small volume extractors; cloud droplet impactors	qPCR total bacteria; qPCR ARG panel; DNA sequencing; Building ventilation properties; Moisture content; Meteorological data	variable, from h to days
Yang, F et al	2021	poultry farms (inside and outside chicken houses)	chickens, humans (18 workers)	bacteria	aerosol samples (Andersen six-stage sampler), cloaca swabs; oropharyngeal swabs of workers	HT-qPCR was performed to evaluate the occurrence of ARGs i	5–10 min air samples; during 1 month.
Rahman, M et al	2020	live bird markets	humans, birds 151 workers	influenza A and B (seasonal and avian)	nasal and troath swabs. NIOSH bioaerosol sampler (BC251); The Coriolis μ air sampler.	rRT-PCR	30 min
Madamarandawala, P et al	2019	Preschols (indoor and outdoor);	146 preschool children aged 3–6 years	Bacteria	Clinical data from children. 1. Fine Particulate Air Sampler; 2. Natural Sedimentation; 3. Single stage viable particle sampler (sterile Whatman and on Luria Bertani agar	LB agar, and the plates were incubated at RT (25 ± 3 °C) along with NSM plates; PCR	1. and 2. 60 min; 3. 2 min, 5 min;
Wang, X et al	2020	Live bird markets	birds	InfluenzaA, B, C, and D	(NIOSH) 2-stage bioaerosol cyclone sampler connected to a SKC AirCheck Touch personal sampling pump	qRT-PCR; viral culture, gene sequencing, and phylogenetic analysis	45–60 min, 2–4 x/ week (October to December)
Ma, M et al	2018	Pig farms	50Pigs; 6 farms workers (399: 299 exposed, 100 controls)	Influenza A-IAV (H1N1), (H3N2) o(H5N6) (H5N1) (H9N2), (H7N9).	Human: a nasal swab; nasal wash specimen; serum. Pig oral secretion; barn environmental swabs; fresh-water samples; pig faecal-slurry samples; aerosol samples. SKC BioSampler	IAV molecular detection, culture, sequencing, microneutralization (MN) serological assays, and immunoglobulin A (IgA) assessments were performed with standard methods	Prospective 5 years sampling 30-min aerosol samples
Wu, D et al	2022	Outdoor air: ventilation outfalls of a large urban hospital; and ambient urban air	NA	Bacteria - ARG	A high-volume PM2.5 sampler (ASM-1, Mingye Inc. China); ventilation output in a large hospital and ambient air PM2.5 samples collected from Guangzhou city (Tianhe (TH) and Conghua (CH) Districts)	DNA paired-end sequencing (150 bp) on an Illumina Hiseq X Ten platform. The deepARG short-read module (v0.18) pipelines were applied to map the profile of the antibiotic resistomes (identified ARGs was normalized to the sequence number of the 16S rRNA gene).	24 h; from April 2016 – May 2017; 2019: June–August; September–December
Han, T, et al	2021	religious facility; household.	Humans, cats; 138 individuals; 3 cats	SARS-CoV-2	Surface samples; nasal, oropharynx, back (i.e., fur), forepaw, rectal,and stool samples (no air samples).	Quantitative real-time reverse transcription PCR (RT-qPCR) assays	December 1st, 2020, to January 10th, 2021
Moor, J et al	2021	26 Pig farms	48 Pigs. 59 pig workers. control group of cattle workers (n = 22).	bacterial Microbiota analysis	Pig farm workers self-collected stools; rectal swabs from pigs. Air sample from the central pen using a Coriolis device	16S rRNA gene sequencing PCR Purification Kit (Qiagen, Hilden, Germany). Samples were passed through to a MiSeq Illumina sequencing platform for indexing and paired-end sequencing (2 × 250 bp; reagent kit, v2).	Oct 2017 Mar 2019 Aerosol: 0.3 m3/min for 10 min
Anderson, B et al	2016	5 Pig farms	Pigs, humans; 130 swine workers; 115 control subjects	Influenza A	bioaerosol, pig oral secretion (by hanging rope method), and environmental swab sampling. Bioaerosol -BioSamplers	Bioaerosol, pig oral secretion, and environmental swab samples - conventional rRT-PCR protocols; Human sera samples: hemagglutination inhibition assay for detection of antibodies against circulating human H1N1 and H3N2 influenza A viruses and swine H1N1 and H3N2 influenza A viruses.	2 weeks (summer) 4 weeks (fall/winter)8 L/min (30 min)
Borkenhagen, L et al	2023	the three largest live bird markets in Yangon	90 live bird market workers; birds	Influenza A and D	Questionnaires (demographics, exposure to live animals, risk and protective behavior. Deep oropharyngeal swabs (birds). Bioaerosol samples - (NIOSH bioaerosol sampler)	Human NP specimens with molecular evidence of IAV were hemagglutinin-subtyped for H1pdm and H3 using rRT-PCR; genetic sequencing of Inflenza A isolates	weekly for 3 weeks - from July 15 to August 7, 2019. 3.5 L/min.
De Andrade, F et al	1	Laboratory - experimental setting	28 Cats	Sporothrix spp	respiratory secretions expelled while sneezing. Skin cytology and culture of skin lesions	culture – Mycosel agar plate (BD) - culture - fungal isolates were identified using morphological characteristics	single-occasion sampling

Table 4.

Evidence gaps identified.

Author	Evidence gaps
Viegas et al., 2023	Assymetric bacterial and fungal contamination in indoor locations of the 2 different countries - portugal and spain. Influence of seasons and ventilations practices; research on the use of fungicides use in agriculture and relation to azole resistant fungi; research on the relation between azole resistance and mycotoxigenic fungi in food commodities
Siegrist, A, et al., 2023	lion-to-human transmission
Kuhlmeier, E et al., 2023	likelihood of more infectiousness from children to animal; relationships between human viral load and period of sampling and animal infection. Evaluate the pontatial of infection by contact with contaminated surfaces/objects, namely manipulation of droppings.
Habibi, N et al., 2023	“This study was limited in capturing the mobile genetic elements associated with these ARGs, that play a key role in the dissemination of ARGs via horizontal gene transfer.”
Laganà, P et al., 2023	Identify determiants of reduction of the presence of Legionella spp. in samples. The study also identifies the need for more improvement of laboratory detection of Legionella
Viegas et al., 2022	However, future studies must accommodate not only the environmental approach, with the EDC placed strategically on the workplace, but also the analysis of the painting, textile, etc., being treated because the conservator works in close proximity to the artefact and shares a micro-atmosphere with the piece itself. Comparing the EDC results with the results obtained by vacuum cleaning, the artefact will possibly increase our knowledge on the particularities of these settings.” future studies an innovative approach (OneHealth approach)—simultaneously targeting workplaces, workers (and users) and the cultural heritage—should be implemented”
George, Paul B.L et al., 2022	n absence of knowledge surrounding airborne communities in natural and built environments, their emission rates in natural environments, and the impacts of anthropogenic change on airborne microorganisms. Explore short-distance spreading and contributions of bioaresols sources. Evaluate long-distance dispersal of bioaerossols and potential impact in agriculturaland sanitaion activities. “adding the role of bioaerosols to an integrated assessment model on AMR”
Yang, F et al., 2023	The study highlights the need of longitudinal health studies to evaluete chegnges in the microbiota of workers exposed to bioaresols containing ARGs/MGEs and potential health effects
Rahman, M et al., 2020	the study identified the presence of viral rNA in both aerosol and human samples. However, it is not possible to distinguish either symptomatic from assymptomatic carriers or the presence of viable virus pesence in airborne particles. Conitnuous monitoring of environment an animals and humans in locations of high risk of novel agents spillover.
Madamarandawala, P et al., 2019	research designed to address viral and fungi contamination of the air, as well as the relation between air microbiota and air pollution
Wang, X et al., 2020	Determination of activities more with most potential to generate aerosolized viral particles in order to identifiy interventions to mitigate the risk. Determination of eficacy and effectivity of bioaresol sampling for detecting novel emergent virus in high zoonotic exposure settings
Ma, M et al., 2018	novel influenza virus surveillance be conducted within swine farms, especially when the farms are large, have poor biosecurity, and can sustain viral transmission. Determination of eficacy and effectivity of bioaresol sampling for detecting novel emergent virus in high zoonotic exposure settings
Wu, D et al., 2022	“t improvements need to be made to the resistome risk ranking method to more clearly label the AMR health hazards to human beings.” “more holistic study remains to be conducted on the AMR hazards and risk rankings of source-specificair PM2.5” “As such, culture-based studies of source specific airborne particles, especially on a larger geographical scale, are warranted to further examine the airborne-resistant pathogens associated with hospitals and the chains linking them to the development of AMR in the surrounding urban communities. Based on estimations of the intake of AMR materials, differences concerning human immunological responses to AMR exposure (respiration vs. digestion systems) should also be included in future risk assessments, particu larly to compare multiple exposure pathways from the ‘One Health’ perspective.”
Han, T, et al., 2021	The study highltghts that transmissio of SARS-CoV-2 between humans ant animals o + is possible under certain circumstances. However, although droplet trnamsmission was assumed, the exact mechanism of transmission could not be identified. Furthermore, as there was no identification of viable virus through culture nor the cat infection was confirmed as true infection, as no serological test was done. “research on the emergence and the observation of new infectious diseases and zoonosis is needed, using the One Health Approach”
Moor, J et al., 2021	To understand the relevance of the airborne transmision of gut microbiota altering agents, as well as the possible implications for human health, including pathogenic transmission
Anderson, B et al., 2016	The work suggests that enviornmental surveillance of swine farms, namely through bioaresol sampling techniques, may be helpflull to detect and characeterize wine inflenza virus. Furthermore, the authors suggest the aplicability of the latter techniques to other animal production industries, particularly by the use of longer-term prospective studies, using One Health approach to establish baseline epidemiological data for the circulation of influenza A viruses in these important ecological settings.
Borkenhagen, L et al., 2023	The work characterizes Influeza viruses present in live bird markets and suggests that the differente lineage of A/H9N2 detected may be the result of the introduction in the country via contaminated birds. I is, therefore, important to consider the monitoring of live markets for novel influeza viruses, considering the possible zoonotic transmission to humans.
De Andrade Galliano Daros Bastos, F et al., 2022	This study proposes a possible novel route of transmission of Sporothrix spp. through feline respiratory secretions expelled during sneezing suggesting that the respiratory droplets produced by sneeze could infect humans and other animals who experienced mucocutaneous exposure. The relative importance of this route is not, however, evaluated in this study, as to the relative size of the particles produced and the possibility of aerossol trnasmission. Likewise, the study does not address the origin of the particles detected in the droplets

3. Results

The literature search yielded 8471 articles from the scientific databases selected (Fig. 1. Search flow diagram). After excluding duplicates, title and abstract screening, and full-text reading, a total of 18 articles were retained for the scoping review (Table 1). All articles were in English.

Fig. 1.

Prisma-ScR diagram flow for Scoping review process.

Table 1.

Concepts and definitions used for the scoping review.

One Health	is an integrated, unifying approach that recognizes interdependence, and aims to sustainably balance, and optimize the health of people, animals, plants and our shared environmental ecosystems. The goal of this collaborative, transdisciplinary approach that considers the local, regional, national, and global levels, is to achieve optimal health outcomes [9,35].
Bioaerosols	refers to the suspended particles in the air (smaller than 100 μm) that contain microorganisms, or their fragments, living or dead, and/or viruses [36].
Indoor Air Quality	refers to the air quality within and around buildings and other structures concerning the health and comfort of occupants in terms of indoor pollution, gases or particles, including biological particles and other contaminants, as well as other characteristics, such as temperature or humidity [37].
Airborne Transmission	refers to the transmission of infectious agents from an infected host to a susceptible organism by air means, particularly considering particles suspended in air smaller than 5–10 μm. Such particles may harbour pathogens and, while remaining suspended in the air for hours, may travel long distances potentially disseminating the infection [2].
Zoonosis	comprises any disease or infection that is naturally transmissible from non-human animals to humans. Zoonotic pathogens represent a major public health problem representing a large proportion of newly identified infectious diseases. Such pathogens may spread to humans through direct contact, water or the environment. Specific contexts increase the risk of zoonotic transmission, namely when a close relationship exists between humans and domestic or wild animals, including poultry production or animal markets.

Key variables of study characteristics according to the PRISMA-ScR Checklist 60—such as author, year, name of the tool or topic of the study, document type, country, and threat—are depicted in Table 2.

The information retrieved from the reviewed studies concerning the review questions is summarized in Table 3.

4. Discussion

4.1. What is the current contribution of the One Health approach to Indoor Air quality and infection control?

The One Health approach is considered an effective method for assessing holistic questions that integrate human, animal, plant and environmental issues. It promotes timely detection and implementation of biosafety measures against emerging infectious threats. The studies reviewed highlight the ability of the One Health approach to address multiple and interconected causes of airborne microbiological contamination [42].

4.1.1. Outdoor/atmospheric studies

While this review focuses on IAQ, it is important to recognize the significance of outdoor air both as a source of contamination for indoor spaces, and a dispersal way for indoor contaminants, airborne agents, or AMR genes [43,44]. The atmosphere connects all terrestrial and marine habitats and species; thus, bioaerosols play a key role in interconnecting ecosystems. The bioaerosols' impact in health arises from the dispersal of animal and plant pathogens, gene flow of antibiotic resistance genes (ARG), and microbially derived allergens [25]. A study by Šantl-Temkiv et al., addressed the ecology of the atmosphere, highlighting the inter-habitat connections and the airborne dispersal of microbial cells, propagules and biomolecules [25]. Comparisons between urban and rural indoor and outdoor bacterial contamination underscore the influence of air quality on the incidence of respiratory illnesses, particularly among preschool children [44].

4.1.2. Zoonosis

Zoonotic infections are one of the subjects in which the One Health approach play a central role, particularly in understanding the bidirectional airborne transmission between humans and animals across diverse contexts and species (Table 2) [20,21,[45], [46], [47], [48]]. Moreover, the One Health approach enhances the importance of continuous environmental monitoring, crucial for infection control and detection of emerging threats, such as Legionella or IAV [20,49,50].

4.1.3. Antimicrobial resistance

AMR is a well-recognized threat to global human Health and a priority environmental concern, acknowledged by the United Nations Environment Program and the WHO. The dispersal of antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARG) has the potential to introduce AMR into regions where no pharmaceutical residues exist, namely by air dispersion [[51], [52], [53]]. The One Health approach is valuable for assessing AGRs in the environment, considering the human-animal-plant-microbe axis to reduce AMR. There is evidence of the presence of AMR in both indoor and outdoor aerosols, with higher concentration indoors [25,49,53].

ARGs are integrated within bacterial DNA found in aerosol samples, with a total load estimated at an average of 10⁵ cells/m³ of air. The number of ARGs was also higher in indoor air, with exhaled air as the most likely source [53]. On poultry farms, the possible transference of ARGs and mobile genetic elements was demonstrated through bioaerosols by evaluating the source (chicken cloaca), the environment (aerosols), and the workers' nasopharynx [18].

When considering outdoor air, it is essential to acknowledge the role of microbial communities, particularly those originating from urban green spaces, as they can have a significant impact on human health. Legionella is a paradigmatic example of a well-known pneumonia agent widely distributed in the environment, and a relevant topic in the One Health context [49].

4.1.4. Emergent threats/airborne viruses

Multiple studies have explored interspecies viral transmission, particularly the potential of aerosolised viral particles spread from animals to humans. Occupational settings involving close human-animal interaction pose an elevated risk for such transmission events [45,46,48]. Well recognized high risk setting for zoonotic transmission of emerging agents include live-bird markets, particularly common in China, and poultry farming units. As such, the detection of emerging airborne agents in these settings are regarded as promising strategy for early detection [20,45,46,48,50,54].

Other studies have investigated the aerosolisation resulting from manipulating infected animals or their waste, including faecal matter [45,46]. However, despite its potential risk for humans, the literature on bioaerosols containing enteric pathogens is scarce [45,55]. Other contexts, such as households, gained relevance in the context of COVID-19 transmission. Investigations using the One Health approach, combining epidemiologic analysis and environmental studies, concluded that the number of SARS-CoV-2 infected households, as well as the presence of children in the household, were associated with a higher infection risk for animals, with cats with no or limited access to the outdoors at higher risk of being infected [19].

4.1.5. Occupational risks

Workplaces, predominantly indoor environments, pose specific risks of exposure to airborne contaminants, particularly microbiological. People often spend extended periods of time in these spaces, often handling materials or working in potentially contaminated environments with poor ventilation. Studies on the subject encompass a variety of settings, ranging from hospitals to poultry farms, live-animal markets, and restoration-conservation settings [20,42,46,48,54,56,57].

Fungi are ubiquitous microorganisms that may thrive even in low-water content environments and can produce mycotoxins that are both toxic to humans and animals. The work by Viegas et al. focuses on the presence of these elements in common workplaces such as grocery stores and conservation-restoration settings [42,56,57].

A large prospective study on pig farms employed the One Health approach to examine influenza A virus (IAV) transmission between pigs and humans by comparing occupationally exposed workers with control groups. Using human, animal and environmental samples, the positive samples yield was approximately 7 % from 4884 samples [45].

4.2. Current research designs and methodological approaches being used in a One Health approach for indoor air quality studies

4.2.1. Epidemiologic studies

In the context of animal infection and the transmission of SARS-CoV-2, epidemiological studies based on contact tracing have identified proximity and environmental contamination as risk factors for infection. Although such studies do not employ direct methods to assess indoor air contamination, they consider close contact and surface contamination (as a result of deposition) as risk factors, thereby implying airborne transmission [19,21,58].

4.2.2. Cross-sectional environmental sampling studies

Total airborne bacterial counts are used to assess air quality, by comparing with national/regional standards. Comparisons between indoor and outdoor air, as well as between urban and rural areas, are important not only for assessing exposure, particularly in preschool children, but also for understanding the potential impact of pollution on air microbiota [44]. Notably, studies have examined associations between indoor and outdoor air contamination in specific settings, such as preschools, in rural and urban areas, with respiratory symptoms and disease prevalence [44].

Investigations for the presence of certain bacteria, such as Legionella spp., are currently performed from a One Health perspective, using water samples, surface swabs, and aerosol collection of vapors/and air/gas mixtures [49].

Identification of airborne microbial contamination in workplaces has been employed to identify agents or toxins potentially harmful to humans. Sampling sites included grocery stores and conservation-restoration facilities. Collection of passive deposition samples using Electrostatic Dust Cloths (EDC) or surface swabs is a straightforward approach for such research [42,56]. Other air sampling methods include cyclonic samplers, such as the NIOSH bioaerosol sampler (BC251) or the Coriolis μ air sampler (Bertin Technologies) to collect air for subsequent rRT-PCR analysis [46]. Additionally, studies on the presence of mycotoxins have been conducted to assess the cytotoxicity of suspended particles in occupational settings [42,56]. Furthermore, studies were undertaken to assess the presence of azole resistance in fungi in the indoor air of non-healthcare workplaces [42,56,57].

Additional methods combined water sampling with aerosol samples of vapors and air/gas mixture in thermal facilities for Legionella identification [49].

Investigation of interspecies transmission, by comparing samples from animals and humans to identify the presence of agents, is of utmost importance to determine the origin of zoonotic spillover [46,47].

Other research designs include periodic monitoring of bioaerosols near high-risk settings, such as poultry farms or live-bird markets [20,42,46,48,54,56,57]. Although some studies do not directly detect the presence of SARS-CoV-2 in airborne particles they infer airborne contamination based on the presence of surface contamination [19,21,58]. A study on cats found that spending time outdoors reduced the likelihood of SARS-Cov-2 transmission from infected humans to cats (anthroponosis). On the contrary, cats SARS-CoV-2 infection increased with human interaction in COVID-19 positive households, particularly those with children, and with positive surface specimens [19].

4.2.3. Antimicrobial resistance dispersal

To study the airborne dispersal of AMR, air samples were collected in a customized device, and qPCR and HT-qPCR analyses were used to identify ARGs. A comparison of indoor and outdoor air across different seasons for the presence of ARGs was used as a One Health approach to address the environmental dissemination of AMR [53].

A multi-year study protocol has been proposed to explore the environmental dissemination of of ARGs across diverse settings. This includes multiple air sampling sites and techniques, exposure models, and long-distance modelling (risk assessment, mouse model, culturomics) [36].

The One Health approach has been used to identify a hospital as a potential source of aerosolized ARGs in the environment, indirectly assessing the indoor setting by comparing the clinical infection burden with the emitted aerosols out of the hospital's ventilation system [43].

Other assessments of ARG dispersal include the comparison, though HT-qPCR, of ARG present in the cloaca of chickens with aerosol samples [18]. Further examples of studies with pigs have investigated how airborne microbial communities may impact human gut microbiota. The authors estimated that a worker could ingest from 6.9 × 10⁵ cfu to 5.5 × 10⁶ cfu during 4 h working in a pig barn [54].

4.2.4. Longitudinal studies

Longitudinal designs are particularly valuable for monitoring viral contamination over time. Studies on IAV using the One Health approach in a prospective cohort addressing human-pig transmission employed serum, human and animal swabs and surface and air environmental samples [45]. These studies may be employed as surveillance tools for identifying known or emerging infectious agents [20,45,49,50].

4.3. Evidence gaps to be addressed by the One Health approach to indoor air quality and environmental quality research

4.3.1. Workplace contamination

Outside healthcare, research on workplace air contamination has not been prioritised as an important biohazard risk in occupational health. Further studies are needed to identify the sources of contamination, from outdoor air to the existing indoor materials [42,56,57]. The One Health approach is crucial for simultaneously investigating workplaces and workers, to identify microbial dissemination, assess occupational infectious risks to workers and implement effective preventive measures. This is especially relevant in contexts such as cultural heritage conservation, livestock production or markets [18,45,56]. Further studies in this area are required to characterize air contamination in different settings and to identify measures to reduce or mitigate the risks, wheter related to pathogens or to ARGs potential transmission.

4.3.2. Zoonotic spillover/emerging infectious agents

Longitudinal environmental sampling is important to reduce infectious risks to humans and predict the emergence of novel agents [45,49,50]. The One Health approach is also vital for detecting novel agents with zoonotic spillover potential, particularly in locations with a high proximity between animals and humans [20,45,46,48]. Avian IAV is a notable example of a potential outbreak-related agent of animal origin where a One Health approach may be helpful in monitoring and early detection [46].

When considering the human-animal interface, especially involving companion animals, it is important to address bidirectional risk factors for viral transmission [19]. Some studies highlight the need for further research to identify infection rather than contamination. Notably, methodology should aim to differentiate between viable and non-viable microorganisms in aerosols, particularly viruses [46].

4.3.3. Airborne dispersal of antimicrobial resistance

The potential health risks posed by the presence of aerosolised sources of ARGs whether in occupational settings or from the environment is still poorly understood. Given the ability of these particles to travel long distances, there is a need to incorporate ambient aerosols into exposure models [25,36,43,49]. To unveil the long-range dispersion and fate of bioaerosols containing ARGs, a team of researchers developed a protocol that includes a broad range of air sampling settings and techniques [36].

An emerging line of research is the study of the impact of airborne biological particles, particularly those containing bacteria, on the gut microbiota of humans or animals. These particles can be deposited in the upper airways and subsequently swallowed [54]. Conversely, some research focused on the characterization of ARGs in aerosols likely derived from the gastrointestinal tract of farmed chickens [18]. Regarding transmission pathways, the One Health approach may be of particular value in exploring the proposed faecal-airborne route, or other possible routes.

4.4. Did COVID-19 impact the one health approach to indoor air quality?

It is worth highlighting the crucial role of the COVID-19 pandemic in raising global awareness of the importance of indoor air quality, especially following the acknowledgement of the airborne route as major driver for the global dispersion of a locally emerging threat. Notably, lockdowns and other measures to contain the spread of the virus led to the suspension of other vigilance activities, including monitoring infectious agents [49,59].

The use of the One Health approach for the direct investigation of COVID-19, particularly through contact tracing and the study of human-animal interactions, has unveiled possible zoonotic spillovers from species that are not usually found in close proximity to humans, such as lions [21]. Nevertheless, despite the significant body of literature emphasising the airborne transmission mode of SARS-CoV-2, most of the studies included in this review have no apparent connection with the COVID-19 pandemic.

4.5. Limitations

Our scoping review design enabled the integration of work from various disciplines. However, the iterative review process covering such a wide array of fields led to a narrowed inclusion process and the potential exclusion of papers that might otherwise be valuable to our overall study goals. We prioritised comprehensiveness and One Health-directed studies over more focused works, such as those specifically focusing on Indoor air quality or the transmission of infectious agents. It is therefore possible that relevant publication addressing similar themes were not included. This might have been a limiting factor, particularly with regard to older studies. However, it was an intentional decision to limit the search to papers where the authors explicitly mentioned the use of the One Health approach, in accordance with the objectives of the scoping review.

The impact of using the One Health approach and the direct results of the investigations were not fully addressed as this was beyond the scope of this review and would be better studied with different review methodologies, such as systematic reviews or meta-analysis.

5. Conclusion

Our scoping review explored themes and methods used specifically in research related to IAQ and infection, under the One Health perspective. This review highlights the diversity of topics, study designs and settings for assessing IAQ. Moreover, the work identified several evidence gaps and different methodologies that may be employed in future studies. Unlike a systematic review, this work did not exhaustively search the literature to gather all the existing literature. Instead, it sought to map current approaches and highlight the relevance of applying a One Health framework in this interdisciplinary field.

Overall, the findings support adopting the One Health approach in studies addressing IAQ and highlight the need for more targeted research under this perspective for a more comprehensive view of a field that intersects multiple disciplines, from biology and veterinary science or agriculture to medicine and engineering.

Our work highlights that planetary health concerns are closely linked to IAQ, demonstrating a bidirectional relation between outdoor and indoor environments, and underscoring the importance of an holistic view of the environment. As the recent pandemic illustrated, local zoonotic spillovers, likely originating outdoors, may be amplified by indoor transmission and globally dispersed. Therefore, a better understanding of the complex interactions between humans, animals and the environment may have a significant impact on global health.

CRediT authorship contribution statement

Gil Correia: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Data curation, Conceptualization. Daniela Calheiros: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Data curation, Conceptualization. Nuno Rosa: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Data curation, Conceptualization. Lisa Rodrigues: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Data curation, Conceptualization. Sandra Cunha: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Data curation, Conceptualization. Luiz Miguel Santiago: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Data curation, Conceptualization. José Costa: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Data curation, Conceptualization. Manuel Gameiro da Silva: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Data curation, Conceptualization. Teresa Gonçalves: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Data curation, Conceptualization.

Funding

The authors affiliated with CiBB are supported by the following funding references: UIDB/04539/2020, UIDP/04539/2020 and LA/P/0058/2020. DC is a recipient of a PhD grant by FCT - Fundação para a Ciência e Tecnologia (Ref 2023.01320.BD). LR is contracted through the reference CEECIND/03530/2017. This work was also supported by COMPETE2030-FEDER-00525700_AIRSECUR, and was sponsored by national funds through FCT – Fundação para a Ciência e a Tecnologia (Foundation for Science and Technology), under the project LA/P/0079/2020, DOI: 10.54499/LA/P/0079/2020″.

Declaration of competing interest

The authors declare there are no conflicts of interest in this project.

Appendix A. Supplementary data

Supplementary material: Data Extraction

Data availability

No data was used for the research described in the article.