Counting On Contact Times

Disinfectants are widely used in healthcare and other settings to kill the microorganisms and pathogens that can cause infections and illnesses. The length of time a particular disinfectant must remain on a surface to do its job effectively is usually known as the contact time but is sometimes called the dwell or kill time.

Contact time is important because different types and concentration of disinfectant will work at different speeds for each pathogen. And some pathogens are harder to kill than others. C.diff spores, for example, generally take longer to kill than the viruses that cause colds, Norovirus or the flu when using the same disinfectant at the same concentration. In practice contact times can be as low as 30 seconds or as high as ten minutes or even longer depending on specific product, pathogen and setting.

A disinfectant must generally remain wet so that its active ingredients can stay in contact with the surface being treated long enough to do their job. If the liquid dries too quickly the disinfectant will become inactive and ineffective. When this happens, some pathogens survive on the surface and remain a potential source of contamination and infection. Further applications are required to maintain the “wetness” for the right amount of time. That is expensive, inefficient and wasteful, especially in settings where the people responsible for disinfection tasks have lots of other things to get on with.

It follows that the best disinfectants are those with contact times shorter than the time they take to dry because these only need one application. Alcohol-based disinfectants are often very effective but they do tend to dry quicker than water-based formulations. Sometimes they dry faster than the contact time which means repeat applications are necessary.

Water-based products (including those containing hypochlorite or hydrogen peroxide) are more likely to remain wet for the right contact time after just one application. But if the contact time is too long these too can dry before they can disinfect properly. Adding larger amounts of liquid in the first place is not usually practical but is also wasteful and inefficient. Disinfectants that work quickly and only need one application are also less likely to be misused or result in non-compliance than products that need repeat applications.

Disinfectants certified for use in healthcare and food settings will generally have passed one or more recognised industry standard “EN” test. They will also have labels and documentation that includes details of their contact times. Reputable suppliers will offer a choice of products and be able to recommend the right one for any given application. They will also be able to supply proper evidence and statutory documentation to support their claims and offer user guides and other training aids to promote compliance and simplicity in use.

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