Prevalence of culturable airborne spores of selected allergenic and pathogenic fungi in outdoor air

Temporal and spatial variations in airborne spore concentrations of selected allergenic and pathogenic fungi were examined in Dublin, Ireland, in 2005. Air samples were taken at four outdoor locations in the city every 2 weeks, coupled with measurements of meteorological conditions. Total culturable airborne fungal spore concentrations in Dublin ranged from 30–6800 colony forming units per cubic metre of air (CFU m−3) over the 12-month period. Cladosporium, Penicillium, Aspergillus and Alternaria spores were constantly present in the Dublin atmosphere, representing >20% of the total culturable spore count. Concentrations of Cladosporium increased significantly in summer and reached allergenic threshold levels, peaking at over 3200 CFU m−3 in August. Penicillium spore concentrations never reached allergenic threshold levels, with average concentrations of <150 CFU m−3. Alternaria conidia formed only 0.3% of the total culturable fungal spore count and concentrations never exceeded 50 CFU m−3, attributable to the coastal position of Dublin and its low levels of arable production. The opportunistic human pathogen Aspergillus fumigatus was present throughout the year in nominal concentrations (<10 CFU m−3), but sporadic high counts were also recorded (300–400 CFU m−3), the potential health implications of which give cause for concern. Spores of neither Cryptococcus neoformans nor Stachybotrys chartarum were detected, but airborne basidiospores of Schizophyllum commune were evidenced by the dikaryotization of monokaryon tester strains following exposure to the air. The relationships between airborne fungal spore concentrations and meteorological factors were analysed by redundancy analysis and revealed positive correlations between temperature and Cladosporium and relative humidity and Penicillium and Aspergillus.