There are no absolute standards, and decisions on whether a building has a fungus problem or not are often made arbitrarily. Methods of collection can give divergent results and are therefore heavily subject to interpretation. Swabbing a sample from a duct or an exhaust grille will yield some concentration of fungal or bacterial cells, but doesn't exactly correlate with airborne concentrations. Measuring airborne concentrations can likewise produce results that depend on interpretation. Often, the testing agencies will not identify the specific microorganisms, but will merely state that colonies were formed, or that there is a potential contamination problem.
Most fungi are unique and have distinctive characteristics.
The photomicrograph at right shows a colony of actinomyces, in which the radiating rays of the mycelium are clearly visible around the central granule. Large-volume air sampling of human respiratory disease pathogens. The assessment of airborne microorganisms. Problems associated with the assessment of airborne microorganisms. Druett, H. A., J. M. Robinson, et al.