Aerosolization of fungal spores in indoor environments

Measurement and prediction of the detachment of Aspergillus niger spores in turbulent flows

Aspergillus niger (A. niger) spores can induce numerous health problems. Once the airflow-imposed drag force on an A. niger spore exceeds its binding force with the colony, the spore is detached. Turbulent flow may considerably increase the spore detachment. No method is currently available for prediction of the drag force on a spore and its detachment in turbulent flows. This investigation measured the turbulent velocities and detachment of A. niger colonies in a wind tunnel. Computational fluid dynamics (CFD) was employed to model an A. niger unit subjected to turbulent flow blowing. The top 1 % quantile instantaneous velocity of the turbulent flow was specified as the steady entry flow boundary condition for solving the peak velocity distribution and the peak drag forces onto spores. The predicted spore detachment ratios were compared with the measurement data for model validation. The results revealed that the spore detachment ratios with a turbulence intensity of 17 % to 20 % can be twice to triple the ratio with a turbulence intensity of approximately 1 %, when the average velocity for blowing remains the same. The proposed CFD model can accurately predict the detachment ratios of the A. niger spores. ENVIRONMENTAL IMPLICATION: Some people are sensitive to the Aspergillus niger (A. niger) spores, and excessive exposure can cause nasal congestion, skin tingling, coughing, and even asthma. Turbulent flow can considerably increase the spore detachment, due to the increased airflow-imposed drag force on the spores during turbulence. This investigation developed a numerical model to solve for the peak velocity distribution and the peak drag forces onto spores in turbulent flows to predict the spore detachment. With the numerical tool, the airborne fungal spore concentrations would be predictable, which paves a way for intelligent and precise control of fungal aerosol pollution.

Bioaerosolization behaviour of potential pathogenic microorganisms from wastewater treatment plants: Occurrence profile, social function and health risks

Wastewater treatment plants (WWTPs) are the leading sources of potential pathogenic bioaerosol that cause non-negligible health risks. However, bioaerosolization behaviour of potential pathogenic microorganisms (PPMs) migrating from wastewater to the atmosphere is still unclear. This study investigated the occurrence profile of PPMs in wastewater, sludge and bioaerosol, then analyzed bioaerosolization level, impact factors and social function. Staphylococcus aureus was selected as the target due to its pathogenicity, and the health risks of workers, engineers and researchers wearing various masks (N90, N95 and medical masks) were evaluated. The results showed that there were 38 and 64 PPMs in bioaerosol from plant A and B. Streptomyces in plant A (average bioaerosolization index, BI= 237.71) and Acinetobacter in plant B (average BI = 505.88) were more likely to migrate from wastewater to the atmosphere forming bioaerosol. Environmental factors (relative humidity, wind speed and temperature) affected both BI and microbial species of PPMs in different ways. PPMs related to fermentation, aerobic chemoheterotrophy, and chemoheterotrophy are the most abundant. Meanwhile microbial networks from plants A and B showed that PPMs were well-connected. Emission level of Staphylococcus aureus bioaerosol can reach 980 ± 309.19 CFU/m3 in plant A and 715.55 ± 44.17 CFU/m3 in plant B. For three exposure population, disease burden (DB) and annual probability infection (Py) of Staphylococcus aureus bioaerosol in two plants were both higher than the U.S.EPA benchmark (10-4 DALYs pppy). All three masks (N90,N95 and medical masks) can decrease Py and DB by at least one order of magnitude. This study illustrated the bioaerosolization behaviour of PPMs comprehensively, which provides a scientific basis for exposure risk prevention and control.

A comprehensive review of microbial contamination in the indoor environment: sources, sampling, health risks, and mitigation strategies

The quality of the indoor environment significantly impacts human health and productivity, especially given the amount of time individuals spend indoors globally. While chemical pollutants have been a focus of indoor air quality research, microbial contaminants also have a significant bearing on indoor air quality. This review provides a comprehensive overview of microbial contamination in built environments, covering sources, sampling strategies, and analysis methods. Microbial contamination has various origins, including human occupants, pets, and the outdoor environment. Sampling strategies for indoor microbial contamination include air, surface, and dust sampling, and various analysis methods are used to assess microbial diversity and complexity in indoor environments. The review also discusses the health risks associated with microbial contaminants, including bacteria, fungi, and viruses, and their products in indoor air, highlighting the need for evidence-based studies that can relate to specific health conditions. The importance of indoor air quality is emphasized from the perspective of the COVID-19 pandemic. A section of the review highlights the knowledge gap related to microbiological burden in indoor environments in developing countries, using India as a representative example. Finally, potential mitigation strategies to improve microbiological indoor air quality are briefly reviewed.

Comparison of bioaerosol release characteristics between windrow and trough sludge composting plants: Concentration distribution, community evolution, bioaerosolization behaviour, and exposure risk

Windrow and trough composting are two mainstream composting methods, but the effect of composting methods on bioaerosol release from sludge composting plants is unclear. The study compared the bioaerosol release characteristics and exposure risks between the two composting methods. The results showed that the bacterial aerosol concentrations in the windrow composting plant ranged from 14,196 to 24,549 CFU/m3, while the fungal aerosol concentrations in the trough composting plant reached 5874 to 9284 CFU/m3; there were differences in the microbial community structures between the two sludge composting plants, and the composting method had a greater effect on bacterial community evolution than on fungal community evolution. The biochemical phase was the primary source of the bioaerosolization behaviour of the microbial bioaerosols. In the windrow and trough composting plants, the bacterial bioaerosolization index ranged from 1.00 to 999.28 and from 1.44 to 24.57, and the fungal bioaerosolization index ranged from 1.38 to 1.59 and from 0.34 to 7.72, respectively. Bacteria preferentially aerosolized mainly in the mesophilic stage, while the peak of the fungal bioaerosolization index appeared in the thermophilic stage. The total non-carcinogenic risks for bacterial aerosols were 3.4 and 2.4, while those for fungi were 1.0 and 3.2 in the trough and windrow sludge composting plants, respectively. Respiration is the main exposure pathway for bioaerosols. It is necessary to develop different bioaerosol protection measures for different sludge composting methods. The results of this study provided basic data and theoretical guidance for reducing the potential risk of bioaerosols in sludge composting plants.

Passive fungal spore release from fruit and vegetable solid waste

Food substrates in municipal solid wastes processing facilities and open dumpsites are a source for the release of fungal spores into air and can cause potential health and climate effects. Experiments were conducted in a laboratory scale flux chamber to measure the fungal growth and spore release from representative exposed cut fruit and vegetable substrates. The aerosolised spores were measured using an optical particle sizer. The results were compared to experiments conducted previously with a test species (Penicillium chrysogenum) on a synthetic media (czapek yeast extract agar). Significantly higher surface spore densities were observed for the fungi on the food substrates as compared to that on the synthetic media. The spore flux was high initially and then decreased on continued exposure to air. The spore emission flux normalised to the surface spore densities indicated that the emission from the food substrates was lower than the emissions from the synthetic media. A mathematical model was applied to the experimental data and the observed flux trends were explained in terms of the model parameters. A simple application of the data and the model to release from a municipal solid waste dumpsite was shown.

A scoping review: What are the cellular mechanisms that drive the allergic inflammatory response to fungal allergens in the lung epithelium?

Allergic airway disease (AAD) is a collective term for respiratory disorders that can be exacerbated upon exposure to airborne allergens. The contribution of fungal allergens to AAD has become well established over recent years. We conducted a comprehensive review of the literature using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to better understand the mechanisms involved in the allergic response to fungi in airway epithelia, identify knowledge gaps and make recommendations for future research. The search resulted in 61 studies for final analysis. Despite heterogeneity in the models and methods used, we identified major pathways involved in fungal allergy. These included the activation of protease-activated receptor 2, the EGFR pathway, adenosine triphosphate and purinergic receptor-dependent release of IL33, and oxidative stress, which drove mucin expression and goblet cell metaplasia, Th2 cytokine production, reduced barrier integrity, eosinophil recruitment, and airway hyperresponsiveness. However, there were several knowledge gaps and therefore we recommend future research should focus on the use of more physiologically relevant methods to directly compare key allergenic fungal species, clarify specific mechanisms of fungal allergy, and assess the fungal allergy in disease models. This will inform disease management and future interventions, ultimately reducing the burden of disease.

Transmission of droplet aerosols in an elevator cabin: Effect of the ventilation mode

The recent outbreak of COVID-19 has threatened public health. Owing to the relatively sealed environment and poor ventilation in elevator cabins, passengers are at risk of respiratory tract infection. However, the distribution and dispersion of droplet aerosols in elevator cabins remain unclear. This study investigated the transmission of droplet aerosols exhaled by a source patient under three ventilation modes. Droplet aerosols produced by nose breathing and mouth coughing were resolved using computational fluid dynamics (CFD) simulations. We adopted the verified renormalization group (RNG) k-ε turbulence model to simulate the flow field and the Lagrangian method to track the droplet aerosols. In addition, the influence of the ventilation mode on droplet transmission was evaluated. The results showed that droplet aerosols gathered in the elevator cabin and were difficult to discharge under the mixed and displacement ventilation modes with specific initial conditions. The inhalation proportion of droplet aerosols for air curtain was 0.016%, which was significantly lower than that for mixed ventilation (0.049%) and displacement ventilation (0.071%). The air curtain confined the transmission of droplet aerosols with the minimum ratios of inhalation, deposition, and suspension and is thus recommended to reduce the exposure risk.

Fungal Aeroallergens-The Impact of Climate Change

The incidence of allergic diseases worldwide is rapidly increasing, making allergies a modern pandemic. This article intends to review published reports addressing the role of fungi as causative agents in the development of various overreactivity-related diseases, mainly affecting the respiratory tract. After presenting the basic information on the mechanisms of allergic reactions, we describe the impact of fungal allergens on the development of the allergic diseases. Human activity and climate change have an impact on the spread of fungi and their plant hosts. Particular attention should be paid to microfungi, i.e., plant parasites that may be an underestimated source of new allergens.

A Method for Capture and Detection of Crop Airborne Disease Spores Based on Microfluidic Chips and Micro Raman Spectroscopy

Airborne crop diseases cause great losses to agricultural production and can affect people's physical health. Timely monitoring of the situation of airborne disease spores and effective prevention and control measures are particularly important. In this study, a two-stage separation and enrichment microfluidic chip with arcuate pretreatment channel was designed for the separation and enrichment of crop disease spores, which was combined with micro Raman for Raman fingerprinting of disease conidia and quasi identification. The chip was mainly composed of arc preprocessing and two separated enriched structures, and the designed chip was numerically simulated using COMSOL multiphysics5.5, with the best enrichment effect at W2/W1 = 1.6 and W4/W3 = 1.1. The spectra were preprocessed with standard normal variables (SNVs) to improve the signal-to-noise ratio, which was baseline corrected using an iterative polynomial fitting method to further improve spectral features. Raman spectra were dimensionally reduced using principal component analysis (PCA) and stability competitive adaptive weighting (SCARS), support vector machine (SVM) and back-propagation artificial neural network (BPANN) were employed to identify fungal spore species, and the best discrimination effect was achieved using the SCARS-SVM model with 94.31% discrimination accuracy. Thus, the microfluidic-chip- and micro-Raman-based methods for spore capture and identification of crop diseases have the potential to be precise, convenient, and low-cost methods for fungal spore detection.

Moldy odor from air conditioners in the residences of Japanese participants with and without asthma

Fungi, a major allergen associated with asthma onset and severity, can contaminate air conditioners if not properly maintained. We surveyed the prevalence and risk factors associated with fungal contamination of air conditioners and patient behavior to reduce this contamination. Japanese adults aged ≥30 years registered in the database of an Internet research company were asked to participate in an online survey. A moldy odor from the air conditioners in their residences was used as an indicator of fungal contamination. Among a total of 1006 adults, including 631 patients with asthma, 37.1% reported a moldy odor from air conditioners. The prevalence was higher in residences with indoor condensation and in air conditioners used for ≥6 years or frequently during the summer, but was lower in air conditioners with an auto-cleaning function. The risk of indoor condensation was higher in apartments, in the presence of an aquarium, and in the absence of a 24-h ventilation system. These risk factors did not differ between the residences or air conditioners of participants with and without asthma. Asthmatic patients were conscious of indoor air quality; however, do not necessarily take appropriate measures to reduce indoor mold contamination, possibly due to a lack of knowledge. In conclusion, appropriate patient education is required to reduce environmental fungal contamination and improve asthma control.