Evaluation of procedures for hygienic hand-disinfection: controlled parallel experiments on the Vienna test model

Controlled parallel experiments were performed on the Vienna test model for the evaluation of procedures for hygienic hand-disinfection in three laboratories (Vienna, Mainz, Birmingham). The degerming activity of four procedures, each taking 1 min, was assessed repeatedly and compared with that of a standard disinfection procedure (ST) using isopropanol 60% (v/v). The mean log reductions (mean log RF) for each procedure were as follows: n-propanol 50% (v/v) 4.85 and 5.14 in Vienna (V) and Mainz (M) respectively, ethanol 70% (v/v) + chlorhexidine-gluconate 0.5% (w/v), 4.01 (V), 3.76 (M) and 4.00 in Birmingham (B). Washing procedures were less effective, mean log RF's of 3.19 (V), 3.49 (M) and 3.04 (B) were obtained with povidone-iodine soap, and 2.91 (V), 3.37 (M) and 3.27 (B) with a liquid phenolic soap. Analysis of variance on the data from Vienna and Mainz revealed significant differences of means not only between procedures ('preparations') but also on repeat testing. To compensate for the influence of variables such as test subjects, laboratory and day, the Vienna test model provides a method of standardization by testing a ST in parallel with the test procedure (P). Standardization of the results was obtained by pair-wise substraction, log RFPi-log RFSTi. Analysis of variance on the resulting values demonstrated that comparability of the results between laboratories and on repeat testing was achieved. The relative variation of the measurements within the laboratories ranged from 0.9 to 4.2%. As assessed by power-analysis, a disinfection procedure will be detected as significantly (P = 0.1) inferior to the standard processes in 95 of 100 experiments if it produces a mean log RF that is at least 0.55-0.65 log units smaller than that of the standard.