Microbial Air Samplers for Meaningful Cleanroom Environmental Monitoring

Abstract

Airborne microbiological concentrations within pharmaceutical cleanrooms are determined by sampling and to maximise the detection of any airborne microbes, it is essential that the sampling is undertaken in locations where there is greatest contamination risk using air samplers that have a verified and appropriate performance. Sampler performance can be assessed by review of both the physical and biological collection efficiencies that are determined by testing. The physical collection efficiency is the ability to collect particles of various sizes and the biological collection efficiency assesses the collection of viable microbes that includes the losses caused by the physical collection efficiency and the detrimental effect that the sampling has on the viability of the captured microbes. Due to the limitations of the established biological collection efficiency test method, this efficiency is only determined for microbes of sub-micron size which are not representative of the larger microbe-carrying particles typically present with cleanrooms. Samplers with a low physical collection efficiency for sub-micron particles are likely to have a poor performance when this test method is utilised and in an attempt to remove this bias from the testing the ‘biological efficiency’, is often reported. This is a measure of the likelihood that any captured microbes would survive, but is often mistaken for the biological collection efficiency and samplers may be utilised in the false belief that they have an appropriate performance. This article provides information regarding air sampler performance testing and reviews the test results reported by the same independent specialist testing company, therefore negating issues resulting from different testing methods, for three different air samplers. The results that are used to determine the ‘biological efficiency’ are examined to provide information relating to the biological collection efficiency of each sampler and to also provide additional information relating to the physical collection efficiency. Improvements to enhance the air sampler testing procedures, to enable a better direct comparison of the performance of different samplers, are suggested.