[Outdoor moulds and respiratory health]

Mould spores constitute the largest portion of biologic particulate matter suspended in the outdoor atmosphere. There is no universal method for collecting airborne mould spores. The most used sampler, Hirst's apparatus, operates continuously and gives results in individual spores per cubic metre of air. Spore concentrations depend on available substrates, human activities such as agriculture, season, diurnal meteorological variations and climate changes. Under natural conditions, concentrations of over 100,000 spores per cubic metre are not exceptional. Cladosporium is the most commonly identified outdoor mould. The association between respiratory health and outdoor mould spore exposure has been assessed in clinical studies, and also by cross-sectional, and less often longitudinal, epidemiological studies. The relationship between asthma exacerbations and specific mould spores has been demonstrated in longitudinal studies. Cross sectional studies have related measurements of mould spore concentrations to severity of bronchial symptoms, drug consumption and peak-flow measurements in groups of asthmatic subjects. Ecological time-series studies use daily indicators of asthma exacerbations (emergency room visits, hospitalizations) within the general population. The moulds mainly incriminated are Cladosporium and Alternaria. They are associated with seasonal, but also perennial, asthma and rhinitis. Further studies are needed to better assess the impact of outdoor moulds on health, particularly basidiomycetes. Studies with molecular biology tools are probably a way forward.