Contribution of particle counting in assessment of exposure to airborne microorganisms

The aim of the study was to determine the relationship between airborne bac terial concentrations and particle counts measured simultaneously at differ ent sites. Andersen single stage viable particle samplers were used for mic robial measurements while a Laser particle counter gave the cumulated count s of particles larger than 0.5 mu m diameter. The first phase of the study was performed in two experimental rooms where the basic level of microbial contamination was low. Peaks of concentrations were generated by human acti vity and both bacterial and particle counts were monitored over 1 h. In the second phase, measurements were run for several days in three different bu ildings normally occupied. Natural variations of bacterial and particle cou nts were monitored: microbial measurements were performed each hour while p article counts were started with a 10 min frequency. Statistics revealed st rong positive correlations between bacterial and particle counts in four si tes out of five. Analyses of covariance used to compare the regression fine s obtained in each area showed that except for two natural sites, the regre ssion lines were significantly different, indicating that no absolute relat ionship can be established between the two parameters. Therefore, particle counting should, of course, not take the place of microorganism measurement s, but combining particle counting with bioaerosols measurements may allow detection of rapid variations instantaneously and indicate further microbia l measurements. This strategy should improve the assessment of people"s rea r exposure to airborne microorganisms. (C) 1999 Elsevier Science Ltd. All r ights reserved.