Advancing the science of bioaerosol exposure assessment.

Research on bioaerosols has experienced, and continues to experience, stellar growth. This is evident in the rocketing number of scientific articles published during recent years (double the number in 2013 compared to 2003 based on keywords on Web of Science and about 10% of the articles in the last volume of Annals of Occupational Hygiene). This outbreak of research is due, among others, to (i) an emerging interest in the role of environmental exposure to biological agents (in public and occupational health), (ii) the development of new biotechnologies used in some industrial sectors, and (iii) the access to news molecular tools allowing finer and faster bioaerosols characterization. Bioaerosols are defined as airborne particles including fungal spores and hyphae, bacteria, endotoxin, β(1→3)-glucans, mycotoxin or high-molecular-weight allergens, and organic dusts in general that is composed of or derived from biological matter. They are found everywhere on earth. Indeed, environmental bacteria, viruses, and fungi are a part of our natural environment, having co-evolved with all the other living organisms, including humans. However, due to the presence of great amounts of organic matter, the release of bioaerosols can be very high in certain industrial sectors (for instance: agriculture, waste management, textile, and wood industries). In addition to infectious diseases, they can also cause allergic, toxic, or irritant reactions. The presence of high levels of bioaerosols is frequently the result of the natural colonization of an organic substrate present in the workplace but may also be integral to the processes at work and are deliberately added (for instance: breweries, wineries, and biotechnology production). Each bioaerosol sample is unique as its composition varies in time and space (abundance and diversity of species, quantity of pro-inflammatory components such as endotoxins and β-d-glucans). This often leads not only to high variation between samples from the same workplace, which can be due to external factors, but also to the dynamic evolution of the colonized substrate and the fast multiplication rate of microorganisms. These variations in airborne concentrations are often considerably large compared to chemical pollutants. Bioaerosols from some typical work sectors are associated with well-known diseases (for instance: farmer's lung in agriculture or the byssinosis in cotton industry). In this issue, four articles focus on bioaerosol problems in four very different workplaces. In two studies (Madsen et al., 2014; Simon and Duquenne, 2014), bioaerosols were measured in occupational situations where microorganisms are used deliberately: as agents of cheese maturation …