We inoculated FFRs with a high bacterial burden to simulate clinical situations such as pneumonia, in which secretions may contain upwards of 107 CFU per gram of sputum.23 At high cell densities, H2O2 degradation can occur via catalase enzymes produced by S. aureus soon after exposure and can contribute to their persistence.24 Recently, Ibáñez-Cervantes et al6 reported that S. aureus was not recoverable from 3M 8210 model FFRs when inoculated at concentrations of 102–106 CFU and treated by the STERRAD NX system, which is discordant with our study. Here, CAT is linked to susceptibility to pneumonia measurement.