Seasonality and diversity of airborne Aspergillus in the outdoor air of Badajoz

Abstract

The airborne presence of Aspergillus in both outdoor and indoor air is important from the point of view of environmental and public health. The aim of this work was to study the seasonal presence of Aspergillus in outdoor air using viable methods. The exterior atmosphere of the city of Badajoz (SW Spain) was sampled at the University of Extremadura for two years from March 25, 2009, to March 25, 2011, using 3 types of viable portable volumetric samplers: two Burkard samplers–one provided with a device having a conical structure (Bd) and another one fitted with a sieve (Bs)– and one Sampl’air sampler (AES). The aspiration flow rate was 20 liters per minute for the Burkard samplers and 100 liters per minute for the AES sampler. Two kinds of culture media were used: Agar Dextrose Sabouraud (SDA) and Agar Extract Malt (MEA). During the first sampling period (March 25, 2009 - March 26, 2010) sampling was done with Bd and Bs and with SDA, whereas during the second sampling period (March 30, 2010 - March 25, 2011) AES and Bs and MEA were used. Data are provided in colony-forming units per cubic meter (CFU/m³). A total of 610 colonies of Aspergillus were counted during the overall period. The daily average concentration was 17 CFU/m³ throughout the period. A total of 15 Aspergillus species were identified, the most frequent being, in descending order: A. niger, A. candidus, A. fumigatus, A. niveus and A. versicolor. Some species were characterized by marked seasonality, predominating during autumn or winter or being absent in the summer. Others showed no marked seasonality. On average, Aspergillus concentration was highest in autumn and lowest in spring; the values in summer and winter were intermediate. Significant differences were found considering the three samplers used (χ²=28.491, p<0.001).