Airborne microbial monitoring in an operational cleanroom using an instantaneous detection system and high efficiency microbial samplers

The airborne microbial contamination in a non-unidirectional airflow cleanroom, occupied by personnel wearing either full cleanroom attire or only cleanroom undergarments was simultaneously determined using an instantaneous microbial detection (IMD) system and efficient microbial air samplers that detected both aerobic and anaerobic microbes. Depending on the type of cleanroom clothing, the IMD system recorded between 7 to 94 times more ‘biological’ particles than microbe carrying particles (MCPs) recovered by the air samplers. Change in the airborne concentration of ‘biological’ particles due to the different clothing was not consistent with the change in the concentration of MCPs. The median size of the ‘biological’ particles was smaller than the MCPs and the associated particle size distributions were considerably different. A number of sterile materials in the cleanroom were shown to disperse substantial quantities of ‘biological’ particles and it was concluded that the number of particles of microbiological origin, and the relationship between the counts of ‘biological’ particles to MCPs, were masked by non-microbial fluorescent particles dispersed from these materials. Consequently, adequate monitoring of this type of cleanroom operation to confirm appropriate airborne microbiological contamination control, using only an IMD system of the type used for this programme of work, is considered to be unfeasible. However, if the IMD system could be improved to more accurately differentiate between micro-organisms and non-microbial fluorescent particles, or if the dispersion of fluorescent particles from nonmicrobiological cleanroom materials could be reduced, then this system should provide an effective cleanroom airborne monitoring method