Exposure assessment of airborne microorganisms by fluorescence microscopy and image processing.

The purpose of this study was to improve the exposure assessment of airborne microorganisms by means of image processing of fluorescence microscopy images. This technique reduces the analysis time and also offers the opportunity to measure the size distribution of the microorganisms. We developed and implemented an automatic focusing procedure in order to count and size evaluate the microorganisms in the sample. However, automatic focusing was not possible if there were any impurities such as larger particles present. Therefore, manual focusing of the microscope had to be applied in connection with automatic counting and size evaluation when assessing the exposure of workers handling materials containing microorganisms, for example. This is also an improvement as it is faster than the fully manual standard methods. The new methods developed in this study correlated (r2 > 0.85) with the standard method for samples of E. coli and for samples of generated airborne bioaerosols from household waste, although a correction factor is necessary. No correlation was found for samples of generated bioaerosols from composted waste. This work has established a possibility for improving exposure assessment of airborne microorganisms by means of image processing instead of manual counting.