A test for cleaning and disinfection processes in a washer-disinfector

Disinfection processes such as heat, aldehydes or alcohols kill vegetative microorganisms but do not necessarily remove other organic contamination. O rganic residues impair the result of low-temperature sterilisation processe s. Heat-stable organic residues may give rise to clinical symptoms in the p atient. Standards are available in Britain and in Sweden for the examinatio n of cleaning processes in washer-disinfectors. The test substances are art ificial soil or blood. These standards are based on visual inspection of in struments or equipment. They cannot be used for examination of tubular inst ruments, nor can they be quantified. For validation of cleaning procedures a simple quantifiable method, which can be performed in an infection contro l laboratory is needed. We have used suspensions in horse blood of Enteroco ccus faecalis bacteria and Bacillus subtilis spores to test disinfection an d cleaning in a washer-disinfector. Instruments used for laparoscopic surge ry were contaminated with a blood-bacteria suspension containing 10(7) orga nisms/ml and then dried and processed in a washer-disinfector using a regul ar process. Remaining microbial contamination was cultured quantitatively. Nineteen objects were investigated in 10 experiments each. Cleaning, measur ed as log reduction >5-6 of B. subtilis, was achieved on surfaces that were adequately in contact with the water flow in the machine. Disinfection (an d cleaning) measured as log reduction >5-6 of E. faecalis was successful at all points examined. The test method is simple and quantifiable, and can b e used to evaluate and to improve cleaning and disinfection processes.