Abstract

Airborne fungi are dispersed through the air. The aim of this study was to determine the prevalence of airborne fungi in Brazil and understand the relationship between fungal growth and respiratory diseases and infections. We conducted an integrative literature review of studies conducted in Brazil based on searches of the PubMed, MEDLINE-BIREME, SciELO, and LILACS databases for full-text articles published between 2000 and 2022. The searches returned 147 studies, of which only 25 met the inclusion criteria. The most prevalent genera of airborne fungi in Brazil are Aspergillus, Penicillium, Cladosporium, Curvularia, and Fusarium. The studies were conducted in the states of Maranhão, Ceará, Piauí, Sergipe, Mato Grosso, Pernambuco, Rio Grande do Sul, Santa Catarina, Rio de Janeiro, São Paulo, and Minas Gerais. The findings also show the relationship between fungi and meteorological factors and seasonality, the sensitivity of atopic individuals to fungi, and the main nosocomial mycoses reported in the literature. This work demonstrates the importance of maintaining good microbiological air quality to prevent potential airborne diseases.

Key words:
Fungi; Air microbiology; Brazil

Introduction

Fungi are ubiquitous heterotrophic eukaryotic microorganisms. They are widespread in the air, soil, oceans, deserts, glaciers, plants, humans, animals, and even insects. They have a chitin cell wall and cell organizations range from unicellular to highly complex filaments¹1 Naranjo-Ortiz MA, Gabaldón T. Fungal evolution: diversity, taxonomy and phylogeny of the Fungi. Biol Rev 2019; 94(6):2101-2137.^,22 Köhler JR, Hube B, Puccia R, Casadevall A, Perfect JR. Fungi that infect humans. Microbiol Spectr 2017; 5(3):813-843.. Fungi are highly diverse, playing an important role in natural cycles, and fungal metabolites have great biotechnological potential, being exploited to acquire bioproducts such as antibiotics, vitamins, and enzymes used in clinical research³3 Hernandez H, Martinez LR. Relationship of environmental disturbances and the infectious potential of fungi. Microbiol 2018; 164(3):233-241..

Airborne or anemophilous fungi are classified into different genera and species and have spores that remain dry and hydrophobic due to cysteine-rich proteins on their surface⁴4 Cai F, Gao R, Zhao Z, Ding M, Jiang S, Yagtu C, Zhu H, Zhang J, Ebner T, Mayrhofer-Reinhartshuber M, Kainz P, Chenthamara K, Akcapinar GB, Shen Q, Druzhinina IS. Evolutionary compromises in fungal fitness: hydrophobins can hinder the adverse dispersal of conidiospores and challenge their survival. ISME J 2020; 14(10):2610-2624.. Air dispersal requires the presence of propagules, whose dispersal is influenced by temperature, air humidity, volumetric precipitation, atmospheric pressure, and wind speed, as well as vegetation and pollution⁵5 Souza PMS, Andrade SL, Lima AF. Pesquisa, isolamento e identificação de fungos anemófilos em restaurantes self-service do Centro de Maceió/AL. CBioS 2013; 1(3):147-154.^,66 Odebode A, Adekunle A, Stajich J, Adeonipekun P. Airborne fungi spores distribution in various locations in Lagos, Nigeria. Environ Monit Assess 2020; 192(2)87..

Widespread airborne fungal microbiota are associated with adverse health effects⁷7 Dubey T. Indoor air pollution due to mycoflora causing acute lower respiratory infections. Microbiol Resp Syst Infect 2016; 1: 95-112.. The inhalation of fungal spores can cause allergic respiratory diseases such as asthma, rhinitis, and sinusitis⁸8 Martins ODA. Fungos anemófilos e leveduras isolados em ambientes de laboratórios de microbiologia em instituição de ensino superior [dissertação]. Pelotas: Universidade Federal de Pelotas; 2016.. The prevalence of fungi-induced allergic respiratory diseases was estimated to be between 20 and 30% among atopic patients and 6% in the general population⁹9 Priyamvada H, Singh RK, Akila M, Ravikrishna R, Verma RS, Gunthe SS. Seasonal variation of the dominant allergenic fungal aerosols - one year study from southern Indian region. Sci Rep 2017; 7(1):11171.. Alternaria sp., Penicillium sp., Aspergillus sp., and Cladosporium sp. are among the genera most commonly associated with hypersensitivity¹⁰10 Nageen Y, Asemoloye MD, Põlme S, Wang X, Xu S, Ramteke PW, Pecoraro L. Analysis of culturable airborne fungi in outdoor environments in Tianjin, China. BMC Microbiol 2021; 21(1):134..

The diversity of airborne fungal spores varies depending on location (indoor or outdoor), geographic region, and season ¹⁰10 Nageen Y, Asemoloye MD, Põlme S, Wang X, Xu S, Ramteke PW, Pecoraro L. Analysis of culturable airborne fungi in outdoor environments in Tianjin, China. BMC Microbiol 2021; 21(1):134.. Fungal growth is favored by high temperatures and relative humidity, with these conditions triggering greater sporulation and, consequently, a rise in allergic respiratory symptoms⁶6 Odebode A, Adekunle A, Stajich J, Adeonipekun P. Airborne fungi spores distribution in various locations in Lagos, Nigeria. Environ Monit Assess 2020; 192(2)87.^,1111 Grinn-Gofron A, Bosiacka B, Bednarz A, Wolski T. A comparative study of hourly and daily relationships between selected meteorological parameters and airborne fungal spore composition. Aerobiologia 2018; 34(1):45-54..

In general, levels of fungal microbiota in the air in indoor environments is a reflection of the diversity of fungi in the outdoor environment and airborne species are the most frequently observed contaminants in climatized environments¹²12 Sobral LV, Melo KN, Souza CM, Silva SF, Silva GLR, Silva ALF, Wanderley KAA, Oliveira IS, Cruz R. Antimicrobial and enzymatic activity of anemophilous fungi of a public university in Brazil. An Acad Bras Cienc 2017; 89(3):2327-2340.. Poor air quality in enclosed spaces can lead to short- and long-term infections and increase the risk of occupational diseases. Even non-pathogenic fungi pose a risk of causing mycotoxicosis and ear and nail infections¹³13 Abbasi F, Samaei MR. The effect of temperature on airborne filamentous fungi in the indoor and outdoor space of a hospital. Environ Sci Pollut Res 2019; 26(17):16868-16876.. Once introduced into enclosed spaces, spores find suitable substrates to colonize and multiply, presenting a potential occupational biological hazard⁸8 Martins ODA. Fungos anemófilos e leveduras isolados em ambientes de laboratórios de microbiologia em instituição de ensino superior [dissertação]. Pelotas: Universidade Federal de Pelotas; 2016.^,1414 Bezerra GFDB, Gomes SM, Silva MACN, Santos RM, Muniz Filho WE, Viana GMC, Nascimento MDSB. Diversity and dynamics of airborne fungi in São Luis, State of Maranhão, Brazil. Rev Soc Bras Med Trop 2014; 47(1):69-73..

Fungal contamination in hospital environments poses a risk of hospital infection15. More well-known complications caused by fungal infections include invasive pulmonary aspergillosis, allergic fungal sinusitis, otomycosis, and mycotoxin-induced severe toxic reactions, which can lead to death in immunocompromised patients⁹9 Priyamvada H, Singh RK, Akila M, Ravikrishna R, Verma RS, Gunthe SS. Seasonal variation of the dominant allergenic fungal aerosols - one year study from southern Indian region. Sci Rep 2017; 7(1):11171..

The World Health Organization (WHO) highlights the rising global health threat of invasive fungal diseases, emphasizing diagnosis and treatment challenges and reinforcing concerns with their resistance to currently available antifungal agents¹⁶16 World Health Organization (WHO). WHO fungal priority pathogens list to guide research, development and public health action. Geneva: WHO; 2022.. The coronavirus disease (COVID-19) pandemic raised the alert over the incidence of fungal infection comorbidities, with aspergillosis, mucormycosis, and candidemia gaining prominence in the literature¹⁷17 Pal R, Singh B, Bhadada SK, Banerjee M, Bhogal RS, Hage N, Kumar A. COVID-19-associated mucormycosis: An updated systematic review of literature. Mycoses 2021; 64(12):1452-1459..

According to National Health Surveillance Agency (ANVISA) Resolution 9 (January 2003), microbiological contamination is a reference parameter for air quality in indoor climatized environments. The resolution sets a contamination limit of 750 CFU/m3 (where CFU is colony forming units) and an indoor/outdoor (I/O) fungi quantity ratio of ≤ 1.5¹⁸18 Agência Nacional de Vigilância Sanitária (Anvisa). Resolução - RE nº 9, de 16 de janeiro de 2003. Determinar a publicação de orientação técnica elaborada por grupo técnico assessor, sobre padrões referenciais de qualidade do ar interior, em ambientes climatizados artificialmente de uso público e coletivo. Diário Oficial da União 2003; 20 jan..

The aim of this study was to determine the prevalence of airborne fungi in the country, demonstrate the relationship between fungal allergens and respiratory allergies, and understand the relationship between airborne fungi with pathogenic potential and the occurrence of infection.

This work is justified by the need to update knowledge and data on the prevalence of airborne fungal microbiota in Brazil. Integrative reviews of the prevalence of airborne fungi and the human health impacts of these microorganisms have yet to be undertaken in Brazil. The data generated by this study constitute a source of information on air quality, microbial contamination, and airborne disease prevention.

Methods

We conducted an integrative review of the literature involving the following stages: formulation of the guiding question; definition of criteria for article selection; database search; data collection, analysis, and interpretation; and discussion of results. The guiding question was as follows: “What are the main airborne fungi found in Brazil and their correlation with respiratory diseases and fungal infections?”.

Searches were performed of the following databases between February 2021 and December 2022: PubMed; Medical Literature Analysis and Retrieval System Online (MEDLINE), accessed using the Regional Library of Medicine (BIREME) interface; Scientific Electronic Library Online (SciELO); and Latin American and the Caribbean Literature on Health Sciences (LILACS). The review involved the following stages.

First, we performed database searches for studies relating to the topic that met the inclusion and exclusion criteria. The Health Sciences Descriptors (DeCs) “fungos”, “anemófilos”, and “Brasil” were used together with the corresponding Medical Subject Headings (MeSH) in English, “fungi”, “airborne”, and “Brazil”. The inclusion criteria were full-text Brazilian articles available online written in English or Portuguese published in national and international journals between 2000 and 2022. Articles that did not address the guiding question, were unrelated to the study topic, and duplicate papers were excluded.

The second stage consisted of data collection and exportation of references to Rayyan QCRI, a reference selection platform that helps remove duplicates and facilitates the title and abstract screening process. The aim of this stage was to identify articles for full-text screening. Exploratory reading was performed, consisting of rapid reading of the selected articles to ascertain whether the studies met the study requirements. Selective reading was then performed, consisting of a more in-depth analysis of the selected articles.

The third stage consisted of the analysis and interpretation of the study results. The articles were catalogued in a table using the following categories: article title, objectives, and main results. The aim of this stage was to organize the content of the articles to obtain responses to the guiding question.

The fourth stage was the discussion of the results, in which the content of the selected studies is analyzed and discussed drawing on the frame of reference.

Results

The searches returned 147 studies, 122 of which were excluded because they were duplicates, were not related to the study topic, or did not meet the eligibility criteria, resulting in a final review sample of 25 studies (Figure 1).

For the search of LILACS, a combination of the keywords “fungi”, “anemófilos” and “Brasil” were used together with the Boolean operator “AND”. For the MEDLINE-BIREME search, the term “microbiologia do ar” (air microbiology) was used. The searches yielded 15 and 30 articles, respectively.

For the searches of PubMed and SciELO, the terms “fungi”, “airborne”, and “Brazil” were used together with the Boolean operator “AND”, resulting in 86 and 16 articles, respectively.

The studies were categorized in a table containing the following headings: article title, objectives, and main results (Chart 1).

Of the 25 articles reviewed by this study, six were conducted in the South, seven in the Southeast, one in the North, nine in the Northeast, and two in the Midwest (Figure 2). The studies show that Brazil has a high diversity of airborne fungal microbiota and that the diversity of composition varies according to region. The following genera had a high incidence across regions: Aspergillus sp., Penicillium sp., Cladosporium sp., Fusarium sp., Curvularia sp., and Alternaria sp.

While the findings show that the hot climate of the tropics is conducive to the occurrence of airborne fungi, the role relative humidity plays in the dispersal process and fungal growth is not clear. The results suggest that humidity facilitates the concentration of fungi, but excess humidity can have a negative effect on the transport of fungal spores. In contrast, sunlight and wind increase the atmospheric dispersal of spores.

The works compiled in this review make an important contribution to existing knowledge of fungal allergies. Exposure to fungal spores increases the risk of asthma or rhinitis attacks in atopic patients. The studies assessed by this review identified a diverse range of species of fungal aeroallergens associated with respiratory diseases. Besides allergic reactions, the literature has documented fungal infections caused by airborne fungi. Fungi with pathogenic potential from the genera Aspergillus sp., Penicillium sp., and Cladosporium sp. were found in controlled hospital environments. Hospital-acquired infections caused by fungi have a high impact on patient morbidity and mortality, meaning that effective aerobiological monitoring of these settings is essential to prevent infection.

Discussion

The discussion of the selected articles is divided into three categories: a) prevalence of airborne fungi in Brazil; b) Airborne fungi and implications for allergic reactions; and c) Airborne fungi and implications for fungal infections.

Prevalence of airborne fungi in Brazil

Airborne fungi are abundant ubiquitous organisms and have the capacity to produce spores or fungal propagules¹⁹19 Leite Júnior DP, Yamamoto ACA, Amadio JVRS, Martins ER, Santos FAL, Simões SAA, Hahn RC. Trichocomaceae: biodiversity of aspergillus spp and penicillium spp residing in libraries. J Infect Dev Ctries 2012; 6(10):734-743.. Spores are ubiquitous and essential structures for fungal dispersal and colonization. Their concentration, aerodynamic diameter, and taxonomic compositions vary considerably and are greatly influenced by environmental factors such as temperature, relative humidity, and season¹⁴14 Bezerra GFDB, Gomes SM, Silva MACN, Santos RM, Muniz Filho WE, Viana GMC, Nascimento MDSB. Diversity and dynamics of airborne fungi in São Luis, State of Maranhão, Brazil. Rev Soc Bras Med Trop 2014; 47(1):69-73.^,2020 Menezes EA, Trindade ECP, Costa MM, Freire CCF, Cavalcante MDS, Cunha FA. Airborne fungi isolated from Fortaleza City, State of Ceará, Brazil. Rev Inst Med Trop Sao Paulo 2004; 46(3):133-137..

According to the findings of the studies, tropical climates are conducive to fungal growth, with the climate in countries like Brazil resulting in the release of large numbers of spores and generating high concentrations of fungi in the atmosphere¹⁴14 Bezerra GFDB, Gomes SM, Silva MACN, Santos RM, Muniz Filho WE, Viana GMC, Nascimento MDSB. Diversity and dynamics of airborne fungi in São Luis, State of Maranhão, Brazil. Rev Soc Bras Med Trop 2014; 47(1):69-73.^,2121 Mezzari A, Perin C, Santos SA, Bernd LAG. Airborne fungi in the city of Porto Alegre, Rio Grande do Sul, Brazil. Rev Inst Med Trop Sao Paulo 2002; 44(5):269-272.. With suitable levels of oxygen, temperature, and humidity, airborne fungi produce metabolites that favor their development in available substrates¹²12 Sobral LV, Melo KN, Souza CM, Silva SF, Silva GLR, Silva ALF, Wanderley KAA, Oliveira IS, Cruz R. Antimicrobial and enzymatic activity of anemophilous fungi of a public university in Brazil. An Acad Bras Cienc 2017; 89(3):2327-2340.. Current knowledge of the transport of bioaerosols shows that meteorological factors influence the spread of fungal spores, with higher temperatures, sunlight, and wind enhancing airborne dispersal²²22 Cordeiro RA, Brilhante RS, Pantoja LD, Moreira Filho RE, Vieira P, Rocha MF, Monteiro AJ, Sidrim JJ. Isolation of pathogenic yeasts in the air from hospital environments in the city of Fortaleza, northeast Brazil. Braz J Infect Dis 2010; 14(1):30-34.. A positive correlation was found between humidity and fungi quantities, in contrast to older studies pointing to higher spore counts in dry and hot seasons²¹21 Mezzari A, Perin C, Santos SA, Bernd LAG. Airborne fungi in the city of Porto Alegre, Rio Grande do Sul, Brazil. Rev Inst Med Trop Sao Paulo 2002; 44(5):269-272.^,2323 Boff C, Zoppas BCDA, Aquino VR, Kuplich NM, Miron D, Pasqualotto AC. The indoor air as a potential determinant of the frequency of invasive aspergillosis in the intensive care. Mycoses 2013; 56(5):527-531..

There is no consensus in the literature regarding seasonality and spore dispersal. A study in Porto Alegre reported higher spore counts in the summer than in the autumn, while research in Fortaleza demonstrated that the concentration of spores was higher in slightly lower temperatures in January and June²⁰20 Menezes EA, Trindade ECP, Costa MM, Freire CCF, Cavalcante MDS, Cunha FA. Airborne fungi isolated from Fortaleza City, State of Ceará, Brazil. Rev Inst Med Trop Sao Paulo 2004; 46(3):133-137.^,2121 Mezzari A, Perin C, Santos SA, Bernd LAG. Airborne fungi in the city of Porto Alegre, Rio Grande do Sul, Brazil. Rev Inst Med Trop Sao Paulo 2002; 44(5):269-272.. A study evaluating the air quality of ICUs in the South found a pronounced variation in fungi counts between seasons, with the autumn months showing the highest prevalence rates²³23 Boff C, Zoppas BCDA, Aquino VR, Kuplich NM, Miron D, Pasqualotto AC. The indoor air as a potential determinant of the frequency of invasive aspergillosis in the intensive care. Mycoses 2013; 56(5):527-531.. There are stark differences in climate between the South and Northeast of Brazil, making it difficult to establish a pattern of fungal growth. In 2021, Bernardi and do Nascimento corroborated the results of a study in Manaus showing that certain genera are more common in specific seasons, with Cladosporium sp. having higher incidence in the rainy season and Aspergillus sp., Curvularia sp. and Penicillium sp. being more prevalent in the dry season²⁴24 Bernardi E, Nascimento JS. Fungos anemófilos na Praia do Laranjal, Pelotas, Rio Grande do Sul, Brasil. Arq Inst Biol 2005; 72(1):93-97.^,2525 Tiago MRM, Oliveira JAA, Cortez ACA, Souza JVB. Airborne fungi isolated from different environments of a primary school in the city of Manaus, Amazonas, Brazil. Arquiv Asma Alerg Imunol 2018; 2(2):264-269..

Some genera of airborne fungi, such as Alternaria sp., Aspergillus sp., and Cladosporium sp., occur worldwide²⁰20 Menezes EA, Trindade ECP, Costa MM, Freire CCF, Cavalcante MDS, Cunha FA. Airborne fungi isolated from Fortaleza City, State of Ceará, Brazil. Rev Inst Med Trop Sao Paulo 2004; 46(3):133-137.. The distribution of fungi differs according to season and the type of environment (indoor or outdoor)²¹21 Mezzari A, Perin C, Santos SA, Bernd LAG. Airborne fungi in the city of Porto Alegre, Rio Grande do Sul, Brazil. Rev Inst Med Trop Sao Paulo 2002; 44(5):269-272.. This compilation of studies of airborne fungi shows that the same high-incidence genera of fungi were found outdoors in different cities at different times of the year ¹⁴14 Bezerra GFDB, Gomes SM, Silva MACN, Santos RM, Muniz Filho WE, Viana GMC, Nascimento MDSB. Diversity and dynamics of airborne fungi in São Luis, State of Maranhão, Brazil. Rev Soc Bras Med Trop 2014; 47(1):69-73.^,2626 Mezzari A, Perin C, Santos Júnior SA, Bernd LAG, Gesu GD. Airborne fungi and sensitization in atopic individuals in Porto Alegre, RS, Brazil. Rev Assoc Med Bras 2003; 49(3):270-273..

A pioneering study of the prevalence of airborne fungi in Porto Alegre published in 2001 showed that the most prevalent genera were Cladosporium sp., Aspergillus sp., Penicillium sp., Curvularia sp., Alternaria sp., Fusarium sp., and others²¹21 Mezzari A, Perin C, Santos SA, Bernd LAG. Airborne fungi in the city of Porto Alegre, Rio Grande do Sul, Brazil. Rev Inst Med Trop Sao Paulo 2002; 44(5):269-272.. Similar results were found in 2021 in Pelotas, where the following genera were identified: Cladosporium sp. (18.22%),Alternaria sp. (13.84%),Penicillium sp. (10.20%), Curvularia sp. (7.47%), and Aspergillus sp. (3.28%)²⁴24 Bernardi E, Nascimento JS. Fungos anemófilos na Praia do Laranjal, Pelotas, Rio Grande do Sul, Brasil. Arq Inst Biol 2005; 72(1):93-97.. In a similar study in Fortaleza in 2004, the most prevalent genera were Aspergillus sp., Penicillium sp., Curvularia sp., Cladosporium sp., Mycelia sterilia, Fusarium, Rhizopus, Neurospora sp., Rhodotorula sp., and Aureobasidium sp., while in Recife and Natal, cities with identical climates, Aspergillus sp. and Penicillium sp. were the most frequent²⁰20 Menezes EA, Trindade ECP, Costa MM, Freire CCF, Cavalcante MDS, Cunha FA. Airborne fungi isolated from Fortaleza City, State of Ceará, Brazil. Rev Inst Med Trop Sao Paulo 2004; 46(3):133-137.. In São Luís, the most prevalent genera in outdoor environments were Aspergillus sp., Penicillium sp., Cladosporium sp., Curvularia sp., and Fusarium sp.¹⁴14 Bezerra GFDB, Gomes SM, Silva MACN, Santos RM, Muniz Filho WE, Viana GMC, Nascimento MDSB. Diversity and dynamics of airborne fungi in São Luis, State of Maranhão, Brazil. Rev Soc Bras Med Trop 2014; 47(1):69-73. The results of these studies are consistent with the findings of a similar study undertaken in the Metropolitan Area of Sao Paulo, which reported that Penicillium sp. and Aspergillus sp. were the most prevalent species in both indoor and outdoor environments²⁷27 Gonçalves FLT, Bauer H, Cardoso MRA, Pukinskas S, Matos D, Melhem M, Puxbaum H. Indoor and outdoor atmospheric fungal spores in the São Paulo metropolitan area (Brazil): species and numeric concentrations. Int J Biometeorol 2010; 54(4):347-355..

The findings reveal the constant presence of spores from the genera Aspergillus sp., Penicillium sp., Cladosporium sp., Curvularia sp., and Fusarium sp. across Brazil over the ten-year study period.

This review also included studies that demonstrated the prevalence of airborne fungi in indoor environments. A study in the state of Pernambuco evaluating the microbiological quality of environments in a university identified the following genera: Aspergillus sp., Penicillium sp., Talaromyces sp., Curvularia sp., and Paecilomyces sp. The frequency of Aspergillus sp. and Penicillium sp. was 50% and 21%, respectively¹²12 Sobral LV, Melo KN, Souza CM, Silva SF, Silva GLR, Silva ALF, Wanderley KAA, Oliveira IS, Cruz R. Antimicrobial and enzymatic activity of anemophilous fungi of a public university in Brazil. An Acad Bras Cienc 2017; 89(3):2327-2340.. In a study investigating the diversity of airborne fungi in a library in the state of Mato Grosso, Júnior et al. found that Aspergillus sp. was one of the most prevalent fungi, being identified in 89.6% of the samples. Penicillium sp. was identified in 10.4% of the samples¹⁹19 Leite Júnior DP, Yamamoto ACA, Amadio JVRS, Martins ER, Santos FAL, Simões SAA, Hahn RC. Trichocomaceae: biodiversity of aspergillus spp and penicillium spp residing in libraries. J Infect Dev Ctries 2012; 6(10):734-743.. Another study that monitored the microbiota of the air in a library in São José do Rio Preto in 2020 identified Aspergillus sp., Cladosporium sp., Penicillium sp., Scopulariopsis sp., and Trichoderma sp.²⁸28 Duo Filho VB, Siqueira JPZ, Colombo TE. Monitoramento de fungos anemófilos no ambiente de uma biblioteca no município de São José do Rio Preto - SP, Brasil. Arq Cienc Saude UNIPAR 2020; 24(2):75-80. Similarly, a study in Rio de Janeiro evaluating the impact of the demolition of a hospital wing on the concentration of fungi found that the most frequent genus was Cladosporium sp. (mean of 45.09 CFU/m³ of air), followed by Penicillium sp. (mean of 14.35 CFU/m3) and Aspergillus sp. (mean of 9.22 CFU/m3)²⁹29 Barreiros G, Akiti T, Magalhães ACG, Nouér SA, Nucci M. Effect of the implosion and demolition of a hospital building on the concentration of fungi in the air. Mycoses 2015; 58(12):707-713..

Airborne fungi can be used as bioindicators for environmental monitoring³⁰30 Schoenlein-Crusius IH, Trufem SFB, Grandi RAP, Milanez AI, Pires-Zottarelli CLA. Airborne fungi in the region of Cubatão, São Paulo State, Brazil. Braz J Microbiol 2001; 32(1):61-65.. A study conducted in 2020 investigating correlations between airborne fungi and air pollutants found that a reduction in the circulation of vehicles due to a truck driver strike had an influence on fungal growth. During the strike, there was an 80% increase in the number of atmospheric fungi, representing a significant difference (p < 0.05) when compared to previous periods before the strike³¹31 Castro e Silva DM, Marcusso RMN, Barbosa CGG, Gonçalves FLT, Cardoso MRA. Air pollution and its impact on the concentration of airborne fungi in the megacity of São Paulo, Brazil. Heliyon 2020; 6(10):e05065..

Airborne fungi and implications for allergic reactions

Fungal spores are aeroallergens that can be inhaled and are associated with various respiratory diseases, including allergic rhinitis and allergic asthma20. Groups of fungi that release airborne spores include zygomycetes, ascomycetes, basidiomycetes, and deuteromycetes. It is in the latter group that the allergens Aspergillus sp., Penicillium sp., Cladosporium sp., and Alternaria sp. are found²⁶26 Mezzari A, Perin C, Santos Júnior SA, Bernd LAG, Gesu GD. Airborne fungi and sensitization in atopic individuals in Porto Alegre, RS, Brazil. Rev Assoc Med Bras 2003; 49(3):270-273..

Human beings are constantly exposed to bioaerosols and fungal spores during their personal and professional lives, constituting a potential occupational biological hazard¹⁴14 Bezerra GFDB, Gomes SM, Silva MACN, Santos RM, Muniz Filho WE, Viana GMC, Nascimento MDSB. Diversity and dynamics of airborne fungi in São Luis, State of Maranhão, Brazil. Rev Soc Bras Med Trop 2014; 47(1):69-73.. High concentrations of spores in the air can lead to hypersensitivity of the respiratory tract and increase symptoms that are typical of the sick building syndrome, such as pneumonia, allergic rhinitis and sinusitis, lack of concentration, and fatigue²³23 Boff C, Zoppas BCDA, Aquino VR, Kuplich NM, Miron D, Pasqualotto AC. The indoor air as a potential determinant of the frequency of invasive aspergillosis in the intensive care. Mycoses 2013; 56(5):527-531.^,3232 Mobin M, Salmito MDA. Microbiota fúngica dos condicionadores de ar nas unidades de terapia intensiva de Teresina, PI. Rev Soc Bras Med Trop 2006; 39(6):556-559..

Skin tests and measures of specific IgE antibody levels for airborne fungi were used in a study in Porto Alegre, which demonstrated that 15.38% of atopic individuals with asthma and/or rhinitis had sensitivity to airborne fungi²⁶26 Mezzari A, Perin C, Santos Júnior SA, Bernd LAG, Gesu GD. Airborne fungi and sensitization in atopic individuals in Porto Alegre, RS, Brazil. Rev Assoc Med Bras 2003; 49(3):270-273.. A study in São Luís with 100 children reported increased concentrations of IgE in 96.9% of patients with allergic asthma and/or rhinitis. Seventy-five per cent of the children tested positive for Aspergillus, 87% for Penicillium, 46% for Neurospora, and 45% for Fusarium³³33 Bezerra GFDB, Haidar DMC, Silva MACN, Muniz Filho WE, Santos RM, Rosa IG, Viana GMC, Zaror L, Nascimento MDSB. IgE serum concentration against airborne fungi in children with respiratory allergies. Allergy Asthma Clin Immunol 2016; 12(1):18.. A similar study in São Luís analyzing IgE antibody levels against airborne fungi in atopic adults found that 79.7% tested positive for Penicillium, 77.8% for Neurospora, and 44.9% for Aspergillus³⁴34 Bezerra GFDB, Almeida FC, Silva MACN, Nascimento ACB, Guerra RNM, Viana GMDC, Muniz Filho WE, Costa MR, Zaror L, Nascimento MDB. Respiratory allergy to airborne fungi in São Luís-MA: clinical aspects and levels of IgE in a structured asthma program. J Asthma 2014; 51(10):1028-1034..

In a study in Fortaleza that performed skin tests on individuals with respiratory allergies using fungal extracts, all patients had positive reactions to extracts of Aspergillus, Alternaria, and Drechslera and 70% had positive reactions to extracts of Penicillium and Curvularia. None of the patients from the control group had positive skin test reactions35.

The characterization of airborne fungal microbiota helps guide epidemiological research and the diagnosis and treatment of allergic reactions¹²12 Sobral LV, Melo KN, Souza CM, Silva SF, Silva GLR, Silva ALF, Wanderley KAA, Oliveira IS, Cruz R. Antimicrobial and enzymatic activity of anemophilous fungi of a public university in Brazil. An Acad Bras Cienc 2017; 89(3):2327-2340.. The allergies addressed by the studies demonstrate the capacity of airborne fungi to cause reactions in individuals who are predisposed to producing IgE response to environmental allergens.

Airborne fungi and implications for fungal infections

It is known that airborne fungi are important biological air contaminants; however,

according to ANVISA, the presence of pathogenic or toxigenic species in the air is unacceptable when assessing the air quality of indoor environments¹⁸18 Agência Nacional de Vigilância Sanitária (Anvisa). Resolução - RE nº 9, de 16 de janeiro de 2003. Determinar a publicação de orientação técnica elaborada por grupo técnico assessor, sobre padrões referenciais de qualidade do ar interior, em ambientes climatizados artificialmente de uso público e coletivo. Diário Oficial da União 2003; 20 jan.. Fungal infections caused by airborne microorganisms, especially hospital-acquired infections, have received much attention in the medical literature in recent years. The patients most affected by opportunistic mycoses are immunocompromised patients, such as cancer, transplant, AIDS, and polytraumatized patients and neonates³⁶36 Bortoluzzi BB, Maciel CG, Reis D, Freitas J. Estudo da microbiota fúngica do ar em três ambientes de uma Universidade em Santa Catarina. Rev Prev Infec Saude 2020; 6:9833.^,3737 Belizario JA, Lopes LG, Pires RH. Fungi in the indoor air of critical hospital areas: a review. Aerobiologia 2021; 37(3):379-394.. Nosocomial infections are particularly associated with fungi from the following genera: Aspergillus sp., Cladosporium sp., Paecilomyces sp., Penicillium sp., and Scopulariopsis sp., and, to a lesser extent, Candida sp., Rhodotorula sp., Cryptococcus sp., and Trichosporon sp.²²22 Cordeiro RA, Brilhante RS, Pantoja LD, Moreira Filho RE, Vieira P, Rocha MF, Monteiro AJ, Sidrim JJ. Isolation of pathogenic yeasts in the air from hospital environments in the city of Fortaleza, northeast Brazil. Braz J Infect Dis 2010; 14(1):30-34.

A quantitative evaluation of fungi in the air of three ICUs in Porto Alegre showed a marked predominance of the genera Cladosporium sp. in indoor environments and Penicillium sp. in outdoor environments, followed by species from the genus Aspergillus sp. (predominantly A. fumigatus, A. niger, and A. flavus)²³23 Boff C, Zoppas BCDA, Aquino VR, Kuplich NM, Miron D, Pasqualotto AC. The indoor air as a potential determinant of the frequency of invasive aspergillosis in the intensive care. Mycoses 2013; 56(5):527-531.. These results are similar to those of a study conducted in an ICU in Pelotas, which found that the most prevalent genera werePenicillium, Aspergillus, and Cladosporium¹⁵15 Gonçalves CL, Mota FV, Ferreira GF, Mendes JF, Pereira EC, Freitas CH, Vieira JN, Villarreal JP, Nascente PS. Airborne fungi in an intensive care unit. Brazilian J Biol 2018; 78(2):265-270..

Similar results were found in a study in an ICU in Mato Grosso, which reported that the most frequent genera were Aspergillus sp., Penicillium sp., and Cladosporium sp.³⁸38 Almeida Alves Simões S, Júnior DPL, Hahn RC. Fungal microbiota in air-conditioning installed in both adult and neonatal intensive treatment units and their impact in two university hospitals of the Central Western Region, Mato Grosso, Brazil. Mycopathol 2011; 172(2):109-116. A study in the surgical center and adult and neonatal ICUs in a hospital in Araraquara found that the most prevalent genera were Cladophialophora sp., Fusarium sp., Penicillium sp., Chrysosporium sp., and Aspergillus sp.³⁹39 Martins-Diniz JN, Silva RAM, Miranda ET, Mendes-Giannini MJS. Monitoring of airborne fungus and yeast species in a hospital unit. Rev Saude Publica 2005; 39(3):398-405.

In contrast, a study of ICUs and wards in two hospitals in Fortaleza isolated four genera of yeast not found in studies in the south of the country: Candida sp., Rhodotorula sp., Trichosporon sp., and Saccharomyces sp.²²22 Cordeiro RA, Brilhante RS, Pantoja LD, Moreira Filho RE, Vieira P, Rocha MF, Monteiro AJ, Sidrim JJ. Isolation of pathogenic yeasts in the air from hospital environments in the city of Fortaleza, northeast Brazil. Braz J Infect Dis 2010; 14(1):30-34. A study in Sergipe isolated four genera of fungi in the surgical center, four in the intensive care center, four in the IUC, and five in the burn unit. The following genera were found: Aspergillus sp. (43%), Penicillum sp. (12%), Fusarium sp. (11%), Candida sp. (6%), and Curvularia sp. (5%)⁴⁰40 Venceslau EM, Martins RPP, Oliveira ID. Frequência de fungos anemófilos em áreas críticas de unidade hospitalar de Aracaju, Sergipe, Brasil. Rev Bras Anal Clin 2012; 44(1):26-30.. Finally, a study evaluating air conditioners in public and private ICUs in the state of Piauí, in the northeast region, found that the predominant genus was Aspergillus sp. The most prevalent species was A. niger, followed by A. fumigatus, Trichoderma koningii, A. flavus, and A. tamarii³²32 Mobin M, Salmito MDA. Microbiota fúngica dos condicionadores de ar nas unidades de terapia intensiva de Teresina, PI. Rev Soc Bras Med Trop 2006; 39(6):556-559..

The results of this review demonstrate a high diversity of fungal microbiota in the air of hospital environments in Brazil, with the predominance of the genera Aspergillus sp., Penicillium sp., Cladosporium sp., Fusarium sp., and Candida sp. Aspergillus sp. makes an evident contribution to the composition of this microbiota and implications include occupational health problems and infection.

The toxicity of species from the genera Aspergillus sp., resulting from their capacity to produce aflatoxin that can cause poisoning, is widely documented in the literature³⁶36 Bortoluzzi BB, Maciel CG, Reis D, Freitas J. Estudo da microbiota fúngica do ar em três ambientes de uma Universidade em Santa Catarina. Rev Prev Infec Saude 2020; 6:9833..

Aspergillosis is a type of mycosis caused by the inhalation of spores from the genus Aspergillus sp., which can develop into allergic bronchopulmonary aspergillosis and other invasive and systemic conditions. The etiologic agents most involved in these conditions are A. fumigatus, A. flavus, and A.niger¹⁹19 Leite Júnior DP, Yamamoto ACA, Amadio JVRS, Martins ER, Santos FAL, Simões SAA, Hahn RC. Trichocomaceae: biodiversity of aspergillus spp and penicillium spp residing in libraries. J Infect Dev Ctries 2012; 6(10):734-743.^,3232 Mobin M, Salmito MDA. Microbiota fúngica dos condicionadores de ar nas unidades de terapia intensiva de Teresina, PI. Rev Soc Bras Med Trop 2006; 39(6):556-559.. Invasive aspergillosis is common in patients with neutropenia and chronic obstructive pulmonary disease and has been increasingly identified in non-neutropenic patients admitted to ICUs²³23 Boff C, Zoppas BCDA, Aquino VR, Kuplich NM, Miron D, Pasqualotto AC. The indoor air as a potential determinant of the frequency of invasive aspergillosis in the intensive care. Mycoses 2013; 56(5):527-531.. A. flavus is associated with pulmonary infections in immunocompromised patients, A. fumigatus is the main agent involved in aspergillosis, and A. niger is frequent in otomycosis³²32 Mobin M, Salmito MDA. Microbiota fúngica dos condicionadores de ar nas unidades de terapia intensiva de Teresina, PI. Rev Soc Bras Med Trop 2006; 39(6):556-559..

The genus Cladosporium sp. is also common in hospital environments. This fungus influences seasonal allergies and is associated with central nervous system infections such as the formation of brain abscesses⁴¹41 Boniek D, Abreu CS, Santos AFB, Stoianoff MAR. Evaluation of microbiological air parameters and the fungal community involved in the potential risks of biodeterioration in a cultural heritage of humanity, Ouro Preto, Brazil. Folia Microbiol (Praha) 2021; 66(5):797-807..

Another genus commonly found in hospital environments is Penicillium sp. Though widely known for its role in the development of antimicrobials, this genus includes fungal air pollutants that can cause penicilliosis when inhaled by immunosuppressed individuals. This disease initially affects the lungs and develops into a systemic disorder¹²12 Sobral LV, Melo KN, Souza CM, Silva SF, Silva GLR, Silva ALF, Wanderley KAA, Oliveira IS, Cruz R. Antimicrobial and enzymatic activity of anemophilous fungi of a public university in Brazil. An Acad Bras Cienc 2017; 89(3):2327-2340.^,1919 Leite Júnior DP, Yamamoto ACA, Amadio JVRS, Martins ER, Santos FAL, Simões SAA, Hahn RC. Trichocomaceae: biodiversity of aspergillus spp and penicillium spp residing in libraries. J Infect Dev Ctries 2012; 6(10):734-743.^,2323 Boff C, Zoppas BCDA, Aquino VR, Kuplich NM, Miron D, Pasqualotto AC. The indoor air as a potential determinant of the frequency of invasive aspergillosis in the intensive care. Mycoses 2013; 56(5):527-531.. Penicillium sp. is also associated with disseminated infections, such as multiple brain abscesses, peritonitis, and pneumonia in immunocompromised patients¹⁵15 Gonçalves CL, Mota FV, Ferreira GF, Mendes JF, Pereira EC, Freitas CH, Vieira JN, Villarreal JP, Nascente PS. Airborne fungi in an intensive care unit. Brazilian J Biol 2018; 78(2):265-270..

Airborne fungal infections in hospital environments can involve different transmission mechanisms, including the inhalation of fungal spores transported and distributed by contaminated ventilation or air condition systems and contact with surgical wounds, surgical instruments, or the clothing and hands of medical staff ²²22 Cordeiro RA, Brilhante RS, Pantoja LD, Moreira Filho RE, Vieira P, Rocha MF, Monteiro AJ, Sidrim JJ. Isolation of pathogenic yeasts in the air from hospital environments in the city of Fortaleza, northeast Brazil. Braz J Infect Dis 2010; 14(1):30-34.^,3737 Belizario JA, Lopes LG, Pires RH. Fungi in the indoor air of critical hospital areas: a review. Aerobiologia 2021; 37(3):379-394.. This review focused on airborne fungi and therefore the most documented mode of transmission is certainly inhalation.

The literature underlines that air conditioning systems are key sources of dissemination of fungal spores, highlighting the importance of installing high efficiency particulate air filtration systems in health services as a way to improve indoor air quality³⁸38 Almeida Alves Simões S, Júnior DPL, Hahn RC. Fungal microbiota in air-conditioning installed in both adult and neonatal intensive treatment units and their impact in two university hospitals of the Central Western Region, Mato Grosso, Brazil. Mycopathol 2011; 172(2):109-116.^,3939 Martins-Diniz JN, Silva RAM, Miranda ET, Mendes-Giannini MJS. Monitoring of airborne fungus and yeast species in a hospital unit. Rev Saude Publica 2005; 39(3):398-405..

This study shows the importance of determining the prevalence of fungi in the environment and understanding the different mechanisms through which airborne fungi cause complications, health problems, and even death. Health professionals need to be aware of the various forms of fungal contamination in order to improve health care delivery. It is important to promote the adoption of preventive measures such as the use of personal protective equipment, raising awareness of fungal infections, and investment in adequate ventilation systems, including regular cleaning of air conditioners and the use of filters.

Conclusion

The study of airborne fungi in Brazil is a diverse field and has gained increasing prominence recently. The large concentration of airborne spores in both internal and external environments and potential contamination with airborne microorganisms highlights the importance of this study. The most prevalent genera of airborne fungi in Brazil are Aspergillus sp., Penicillium sp., Cladosporium sp., Curvularia sp. and Fusarium sp. High concentrations of spores in the air can lead to hypersensitivity and symptoms that are typical of the sick building syndrome, such as allergic rhinitis and sinusitis, lack of concentration, and fatigue. Allergic reactions mainly affect atopic individuals. Airborne fungi can be both pathogenic and toxigenic, causing invasive fungal diseases with disastrous consequences for immunosuppressed patients.

Study limitations include only including articles written in Portuguese and English and limiting the focus to Brazil. Unfortunately, there are few studies addressing airborne fungal microbiota in Brazil and therefore the sample of articles selected for this review was not very robust.

Given the importance of the study topic, further research should be conducted in this area in Brazil. This review seeks to contribute to discussions on the development of public health policies addressing microbiological air quality.

References

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