Comparative study of airborne viable particles assessment methods in microbiological environmental monitoring

A comparative study was done among available assessment methods to measure airborne viable particles in controlled rooms. Active methods were compared (sieve/nozzle impactor, slit-to-agar, centrifugal, filtration, and impinger). The comparative study was carried out by means of a two-way (factors: day and method) analysis of variance, after to logarithmical transformation of experimental results in order to fulfill the normality test of the variables. Statistically significant differences were found among the results of the five methods (P < 0.0001). In a post hoc study, by means of Tukey's test, no differences were found among centrifugal, filtration, and impinger methods. Differences were found among all the other methods (P < 0.05). It is concluded that centrifugal, filtration, and impinger methods (in which numerical results were higher than in the others) may be the most suitable methods for microbiological monitoring of a clean room. The mean results among the three selected active methods were compared with results on the settle plate (SP) (the passive method). A relationship was established between results of the passive method (CFU/h/plate 90 mmø) and the results of active methods (CFU/m3 air). By means of a lineal regression study, it was obtained a relation factor of 22.7; (95% CI: 19.7, 25.7). This factor is only valid for values between 3 and 16 in CFU/h/plate 90 mmø, and it is put on record that the experimental study took place in a room that fulfills Class D clean room specifications (WHO standards) in microbiological terms.