Measurement of Indoor Bioaerosol Levels by a Direct Counting Method

Research of indoor biocontamination is motivated by the potential for bioaerosols to cause human illness. Several methods have been used for sampling indoor bioaerosol levels. For screening or characterization purposes of indoor bioaerosol contamination, the Andersen viable (microbial) particle sizing sampler, the portable Reuter centrifugal sampler, and the gravitational collectors (agar-filled petri plates) are among the frequently used samplers. These conventional methods require an incubation period of about 2-7 d. An effort was undertaken to develop a measuring technique for screening purposes that would eliminate the incubation "wait time." The filtration fluorescence direct counting method was developed, tested in the laboratory, and applied in a pilot field study. The filtration fluorescence direct counting method is a modified six-stage Andersen viable sampler that uses sterilized water instead of culture medium in each petri dish. After sampling, water is filtered and the filter is stained with acridine orange for direct counting of bioparticles under a fluorescent microscope. This technique for measuring bioaerosol eliminates the necessity for incubation and provides a measure of total bioaerosol concentration within an hour after sampling. The database generated by the new method compares favorably with data from side-by-side sampling using conventional methods. It is concluded that the method developed is an appropriate screening tool for evaluating the bioburden of indoor and outdoor environments.