Hi Jerry. Using actual pathogen particles is the only acceptable approach. In principle filtration is purely a size selection but that’s not necessarily true in practice where there can be binding of species to internal membrane walls, competitive binding with other species and other complications. Manufacturers and the FDA don’t want to think about this but it’s true. So proxy particle retention is not acceptable since the surface chemistry and binding can be different.
Also, not all pathogen particles are infectious which is particularly true for viruses. So simply counting the fraction that are retained is not relevant, the test needs to be specific to the infectious particle fraction. This also accounts for the potential for pass through of damaged or inactivated pathogen. For example, if non infectious pathogen fragments pass through the filter, that is not hazardous.



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Versa Flow, Sawyer Mico, Hydrapak ..
here side by side including a BeFree
