ABSTRACT

This chapter examines microbiological considerations of filtration in depth. “Worst-case” in the realm of microbiological validation of filters can be a very difficult condition to define, and in the author’s opinion careful scientific analysis regarding appropriate microbial titers for the challenge have been lacking. The true mission of the filter is to adequately abate microbiological risk in terms of infection of the end user, absolute sterility being impossible to establish by this or any other widely applied test including the so-called “sterility test.” Filtration is all too often taken for granted in terms of both performance and outcome due to an overly optimistic belief in worst case challenge testing and a certain naivety regarding the true nature of the microbiological world. Treatises on the filtration of liquids with the objective of achieving a sterile effluent are typically replete with detailed discussions of the physical and chemical characteristics of filters and the various mechanisms at play in retention.