Poly(styrene–divinylbenzene)-4-(methyltrimethylammonium) triiodide (PMT) has recently been applied onto nonwoven air filter media to purportedly combine filtration and iodine disinfection to achieve enhanced attenuation of viable airborne pathogens without aggravating the pressure drop of the medium. This paper reports and compares the physical capture efficiency and biological removal efficiency of the novel biocidal filter medium. During challenges with inert fluorescent particles, both iodine-treated and untreated media displayed statistically equivalent physical capture efficiencies > 97%, and typically > 99%. The pressure drag (3.2 kPa•s/m) was less than 10% that of a glass fiber HEPA (38 kPa•s/m) medium. Biological disinfection by the media was evaluated using aerosols containing M. luteus and E. coli vegetative bacterial cells. Biological removal efficiency (99.997%) was observed to be two logs greater than inert particle capture. Viable penetration through the biocidal filters was observed in only two of 10 experiments. The results suggest that an antimicrobial-coated filter medium can provide effective protection against airborne pathogens with a significantly lower pressure drop than that imposed by conventional high-efficiency filtration systems. A near-contact mechanism is proposed in which the distances of nearest approach to treated fiber surfaces as a microbe penetrates through the filter define the probability that charge sites on the microbe’s surface will capture enough iodine molecules from triiodide complexes at the surfaces to terminate viability.