In-use tests of disinfectants.

In two different laboratories three methods were applied for in-use testing of 400 samples of disinfectants, primarily aldehyde and phenolic solutions, collected in 30 wards at 11 Danish hospitals. The results obtained with the Kelsey-Maurer test, the membrane filtration technique, and a standardized challenge test were in complete accordance, however, the challenge test revealed a few more inefficient samples, than the two other methods. For routine use at hospital laboratories the choice between the Kelsey-Maurer test or the modified Kelsey-Maurer technique using membrane filtration may be guided by the available equipment. The design and the application of a challenge test and pertinent criteria for test strains are discussed. Only about 3% of the samples failed to pass the tests, but a predominance (10%) of failures among the samples, received as number one in a series, underlines the didactic aspects of in-use testing. The study demonstrates that suitable methods exist and may be of value when introduced in the local policy of controlling disinfectants.