The conditions of “Justified disinfection”

For a surface to present a risk of transmission of microbial disease, it must be able to serve as a vehicle between a microorganism and humans. For example, floors, urinals, ceilings and most walls cannot typically be used as a vehicle because we typically do not touch them. The presence of a pathogenic microorganism on these surfaces therefore does not represent a real biological risk to our health.

In contrast, a door handle, bathroom faucets/taps, toilet flush handles and light switches can present a genuine risk as we touch them frequently and then put our hands to our face and possibly our food. They can be sources of indirect transmission of microorganisms (individual – surface – individual) (CDC, 2016).

What to disinfect: Only surfaces frequently touched with the hands (high touch) should be disinfected as only these surfaces can serve as a vehicle for the transmission of microbial diseases.

When to disinfect: Disinfecting a surface provides immediate but short-lived protection. It will be contaminated again and will have lost its disinfected and safe status as soon as it is touched again – which can sometimes happen a few seconds after disinfection. It has been shown that a disinfected surface can return to its original level of contamination (in terms of microbial load) within 2.5 hours (Attaway et al., 2012) or six hours (Schmidt, Fairey & Attaway, 2019) after its disinfection depending on the microbes present. Indeed, in a hospital setting, disinfection was not found to make a significant difference in the colony numbers of certain bacteria, with microbial surface loads being indistinguishable 30 minutes before and 30 minutes after the disinfection procedure (Frickmann et al., 2017).

Since it would be impractical and excessive to disinfect a surface each time it is touched maintenance programs generally provide one disinfection per day when disinfection is required. This frequency can be increased if necessary depending on the situation and the traffic in a given location.

How to disinfect?

Like everything, if you want to disinfect a surface, you must do it correctly and observe the following application conditions:

• 1. Apply the disinfectant on a recently cleaned surface (the activity of the majority of disinfectants is reduced if used on unclean surfaces; the most effective regimen is precleaning, followed by disinfection [Tuladhar et al., 2012]);
• 2. Use the correct concentration of disinfectant as prescribed by the manufacturer;
• 3. Adhere to the wet contact time prescribed by the manufacturer.

If these conditions are not met you have not properly disinfected the surface and cannot expect to obtain the benefits sought by the disinfection process.