Monitoring viable fungal and bacterial bioaerosol concentrations to identify acceptable levels for common indoor environments

Little characterization of bioaerosol concentrations between 200 and 450 cfu.m(-3) has been carried out to address potential concerns about indoor air quality. The present research describes measurements of indoor bioaerosol concentrations and concludes that a level of nontoxigenic and nonpathogenic organisms less than or equal to 300 cfu.m(-3) should be typical for environments in which normal, nonimmunocompromised people live. With the exception of Cladosporium, no organism should individually contribute more than 50 cfu.m(-3) to the total. The author believes that levels >300 cfu.m(-3) and/or not meeting the above criteria require further investigation for: a bias from prominent outdoor bioaerosol(s), inadequate air filtration, excessive indoor humidity and micro-humidity environments, and/or potential indigenous contamination source(s). This is not to say that a level of contamination >300 cfu.m(-3) represents any threshold having medical or health significance nor necessarily that it is representative of an unacceptable indoor environment. Rather it is proposed as a 'reactionary threshold' to incite further investigation into the cause(s) of what, from the measurements made, is an above average viable concentration for indoor bioaerosols. It is also concluded that outdoor sampling should only be carried out for comparisons with individual indoor components and that indoor/outdoor ratios involving total cfu.m(-3) concentrations should not be used for evaluating acceptable indoor bioaerosol concentrations.