Disinfection by hydrogen peroxide at low concentration in air: The key role of condensation.

Gazeous hydrogen peroxide (H2O2) is commonly used for disinfection of room surfaces or sterilization of medical devices. Disinfection and sterilization processes are controlled by mean values measured at sterilizer chamber or room level. However, the surface phenomena (adsorption/condensation) taking place on inoculum are essential and still not well-known. In the present study, a solution of water and H2O2 is sprayed in a room disinfection system (Glosair 400, ASP) for 12 min. Condensation mass, H2O2 concentration, relative humidity (RH), macro zoom observations and inactivation kinetics of various microorganisms (Staphyloccocus aureus, Pseudomonas aeruginosa Candida albicans, Aspergillus niger) are reported. Macro-zoom observations reveal condensation and bubbling activities. Microbial inactivation is found optimal at low initial RH, corresponding to high H2O2 vapor concentration and low condensed mass. H2O2 concentration in the condensate is high and probably boosted by fractional condensation. In surface disinfection processes, inactivation of microorganisms occurs in presence of condensation although excessive condensation, due to high initial RH conditions or the presence of salt, decreases the microbial inactivation efficiency by dilution. While the present experimental conditions differ from those prevailing in H2O2 sterilization (59 % H2O2 under vacuum) or industrial disinfection processes (30 % H2O2 at atmospheric pressure), they are partially transposable.