Virucidal efficacy of glutaraldehyde for instrument disinfection

Aim: Glutaraldehyde (GDA) is an active ingredient in many instrument disinfectants and is effective against a broad spectrum of microorganisms. In the past, the virus-inactivating properties of these products were mainly claimed based on quantitative suspension tests with different test viruses. Recently, however, a European Norm EN 17111:2018 has been published which allows examination of instrument disinfectants in a surface carrier test, simulating practical conditions. Therefore, it is of interest to evaluate GDA for the ability to inactivate the viruses used in this European Norm as test viruses. Methods: The virucidal efficacy of GDA as the active ingredient in instrument disinfectants was evaluated with 4 different test viruses in a method simulating practical conditions (EN 17111:2018). Results: With a fixed exposure time of five minutes at 20°C, 100 ppm GDA were necessary to inactivate vaccinia virus, classifying it as a limited spectrum virucidal activity for pre-cleaning products. For adenovirus, 125 ppm GDA were required, whereas for murine norovirus as a surrogate for human norovirus, 4,000 ppm GDA were required for a significant reduction of viral titres. Both non-enveloped viruses must be tested to prove virucidal activity in EN 17111:2018. But even 4,000 ppm were not enough to yield a 4 log(10) reduction of the murine parvovirus at 20°C. This virus is only required as a test virus using this method if temperatures ≥40°C are used. Conclusion: GDA, as the active ingredient of many instrument disinfectants, shows virucidal efficacy at 20°C. The necessary concentrations are strongly dependent on the stability of the test viruses. Due to the high stability of murine norovirus, GDA levels of 4,000 ppm were required to inactivate this virus within the 5-minute exposure time.