What is contact time?
Removing or killing the organisms on surfaces and equipment like blood pressure cuffs or tourniquets is critical in hospital and healthcare environments. Wet wipe manufacturers conduct tests to determine the time it takes for this to happen (referred to as contact time) and it can vary between 60 seconds to 10 ten minutes depending on the efficacy of the wipe.
What does log reduction mean, and is it relevant in healthcare?
The most common disinfectant claims relating to kill rates are called log reductions. Log is short for the mathematical term logarithm, the ‘power’ to which a number is raised. For example, if the base number is 10, a log 3 reduction is shown as 103 or 10x10x10=1,000.
Why is maths involved in cleaning?
In infection prevention and control, log reductions show how effectively a product reduces the number of microorganisms on a surface. The higher the log reduction, the better at killing the organism/pathogen.
The process adds 9 to the percentage for each log reduction, so a log 6 reduction is better than a log 3, eg 99.9999% is better than 99.9%.
How is this tested?
The efficacy of wet wipes in infection prevention and control is tested in accredited laboratories. As individual bacteria are too small to see, testing technicians count how many colonies of micro-oganisms are present at the start of the test. They then apply the wet wipe against a control product and wait the required contact time before recounting the colonies. These are measured in CFUs - colony forming units that can be seen with the naked eye.
If the number of CFUs in the control group were 1,000,000 (106) and the result after using the wet wipe was 1,000 CFUs, then the log reduction would be 99.9%.