Re-evaluation of current A0 value recommendations for thermal disinfection of reusable human waste containers based on new experimental data

Issues over the correct cleaning and disinfection of reusable medical devices are of great concern for local infection control teams. We investigated the heat resistance of two important micro-organisms implicated in nosocomial infections, Enterococcus spp. and spores of Bacillus subtilis (a surrogate for Clostridium difficile). Disinfection with moist heat, based on the A0 concept (EN ISO 15883-1), is the most common method for disinfection of human waste containers in the hospital setting. The aim of this study was to scrutinise the A0 concept regarding the inactivation of the above-mentioned micro-organisms and to look for possible interferences. Experiments were carried out in phosphate-buffered saline, artificial soil in suspension (ASS) and dried artificial soil (AS). Artificial soil was used to simulate insufficient cleaning of bedpans. Micro-organisms were treated at different temperatures and time periods. It was shown that soil protected the micro-organisms against heat and that dried soil enhanced this effect, probably as a result of thermal insulation. The results of the current study do not support the general recommendation to use an A0 of 60 for the disinfection of bedpans but warrant differential strategies depending on the expected microbial load. We generally recommend for disinfection processes aimed at vegetative bacteria an A0 of ≥180. Furthermore we want to emphasise the utmost importance of not allowing freshly contaminated bedpans to dry for longer time periods, as the significance of thorough cleaning of contaminated human waste containers before being exposed to heat treatment for their disinfection was clearly demonstrated.