AN EVALUATION OF THE REPEATABILITY AND REPRODUCIBILITY OF A SURFACE TEST FOR THE ACTIVITY OF DISINFECTANTS

A collaborative study was carried out to determine the precision of a disinfectant surface test method which is currently under consideratio n for development as a harmonized European standard surface test. Resu lts indicate that significant variation in microbicidal effect occurs both within and between test laboratories despite careful standardizat ion of test conditions, but that the variability may be less than that associated with suspension tests. Indications are that much of this v ariability derives from random variations in the resistance of the tes t strains from day to day and, most particularly, from test period to test period both within as well as between laboratories. It is conclud ed that although the test may be sufficiently reliable to be used as a standard method, adequate replication must be specified to distinguis h borderline pass from borderline fail concentrations.