As large infection outbreaks continue to occur, there is a constant need for evaluation whether air filters and products that claim to reduce pathogens through filtration are actually effective. Until now, however, there was no designated method to test filters directly with actual human pathogenic microorganisms or highly allergenic particles without the previous workaround of surrogate model organisms.

Currently, the filtration efficiency of filter media and filter elements such as indoor cabin filters, is predominantly characterised on filter test rigs or test chambers using standardized, non-biological test dusts & -aerosols, such as ISO 12103-1 A2 fine dust, DEHS or salt particles. The drawbacks of testing with non-biological particles and aerosols, being that they focus on particle size but do not factor in actual inactivation of potential biohazards. Air filtration tests with bioaerosols have been investigated in recent years, however, due to necessary safety precautions, test methods with actual human pathogenic microorganisms in distinctive test rigs are not widely available.

Therefore, a new filter test rig was developed to test not only flat sheet filter media but also filter elements for microbial reduction efficacy directly with human pathogenic microorganisms up to biosafety level 2 (BSL 2) as well as potentially highly allergenic particles. In order to achieve this, it was necessary to down scale the dimensions of the test rig in such a way that it could be fitted under commercially available biosafety cabinets used typically in microbiology laboratories of biosafety level 2, while still generating reproducible results under realistic conditions regarding airflow rates and particle nature. The configuration of the test rig was designed with a modular approach in mind.

By incorporating quickly interchangeable components, the test rig can be used for a great variety of biohazards, from pathogenic bacteria and viruses to highly allergenic fine dusts and pollen. The final test rig was validated against the well-established bioaerosol filtration tests methods currently performed at OFI.

Results demonstrate that it is possible to perform reproducible and highly sensitive tests for determination of microbial and allergenic reduction efficiency of critical human pathogens for a wide range of filter media and filter elements with the novel test rig under representative test conditions. Furthermore, the highly modular configuration opens new pathways for future planned endeavours, such as efficacy testing of air stream UV disinfection devices against airborne human pathogens.