Why is contact so important in the disinfection process

Common contact times for household disinfectants can vary greatly; contact times for products approved by the U. Environmental Protection Agency EPA to be effective against the coronavirus, for example, range from 30 seconds to 30 minutes!

The average contact time for those products is nearly 6. One can then search for products featuring contact times of less than or equal to 1 minute, 5 minutes, 10 minutes, etc. Why do contact times vary so much? Different disinfectants may react differently with pathogens.

Additionally, the concentration of active ingredient s matters. Disinfectants registered with the EPA must document evidence of their effectiveness when applied according to label use directions. The simple fact is that if one does not allow for the correct contact time, the disinfection method may be woefully ineffective.

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Contact times for disinfectants range from 15 seconds to ten minutes, the maximum time allowed by the EPA. Disinfecting products usually include directions that instruct users to ensure that the surface is visibly wet for the contact time. This practice does have its challenges though. Keeping a surface visibly wet can be difficult for disinfectants that require a long contact time, such as ten minutes.

Under some conditions, such as high temperatures and low humidity, it can also be difficult even for disinfectants with contact times as short as three or four minutes to stay wet. It is particularly challenging for disinfectants with high alcohol content, which evaporate quickly.

If the disinfectant does dry on the surface before the contact time is reached, label instructions usually require reapplication to ensure that the contact or wet time is met.

If visible wetness for the contact time is not used as a measure of efficacy or as a way to help with compliance, then how would end users know that product application was sufficient to achieve disinfection?

Would the alternative approach be based on the surface area a wipe can cover and still effectively disinfect? This approach would require product labels to include instructions for how much surface area the product can cover and still effectively disinfect and would require users to measure the surface area being wiped to ensure proper use.

If the wipe is used on too large an area, then insufficient disinfectant may be applied, resulting in a failure to effectively decontaminate the surface.

This approach presents a more challenging situation than using visible wetness as an indicator. First, while measuring surface area may be relatively easy on large flat surfaces, hospital room surfaces and equipment are rarely flat and consistent, making it difficult and highly impractical to calculate surface area. Second, wipe sizes and the amount of disinfectant on each wipe varies between products and differences in wipe sizes and surface coverage could create confusion for users trying to monitor areas covered for specific wipes.

For these reasons, requiring the disinfectant to remain visibly wet on the surface is a useful and relatively simple practice to follow to ensure compliance and proper disinfection.

EPA regulations require data to support disinfecting claims. Data requirements are not specific or consistent around the requirement to keep the surface visibly wet for the full contact time and are also dependent on the microorganism against which a claim is obtained. The method even instructs the third-party laboratory to drain excess disinfectant from the carrier once the contact time is reached.

It is also common practice for third-party testing laboratories to cover the carriers after application of the disinfectant to create a closed environment that reduces drying and prevents contamination.

The germicidal resistance exhibited by the gram-positive and gram-negative bacteria is similar with some exceptions e. Rickettsiae , Chlamydiae , and mycoplasma cannot be placed in this scale of relative resistance because information about the efficacy of germicides against these agents is limited Because these microorganisms contain lipid and are similar in structure and composition to other bacteria, they can be predicted to be inactivated by the same germicides that destroy lipid viruses and vegetative bacteria.

A known exception to this supposition is Coxiella burnetti , which has demonstrated resistance to disinfectants With other variables constant, and with one exception iodophors , the more concentrated the disinfectant, the greater its efficacy and the shorter the time necessary to achieve microbial kill.

Generally not recognized, however, is that all disinfectants are not similarly affected by concentration adjustments. For example, quaternary ammonium compounds and phenol have a concentration exponent of 1 and 6, respectively; thus, halving the concentration of a quaternary ammonium compound requires doubling its disinfecting time, but halving the concentration of a phenol solution requires a fold i.

Considering the length of the disinfection time, which depends on the potency of the germicide, also is important. Several physical and chemical factors also influence disinfectant procedures: temperature, pH, relative humidity, and water hardness. For example, the activity of most disinfectants increases as the temperature increases, but some exceptions exist. Furthermore, too great an increase in temperature causes the disinfectant to degrade and weakens its germicidal activity and thus might produce a potential health hazard.

An increase in pH improves the antimicrobial activity of some disinfectants e. The pH influences the antimicrobial activity by altering the disinfectant molecule or the cell surface Water hardness i. Organic matter in the form of serum, blood, pus, or fecal or lubricant material can interfere with the antimicrobial activity of disinfectants in at least two ways. Most commonly, interference occurs by a chemical reaction between the germicide and the organic matter resulting in a complex that is less germicidal or nongermicidal, leaving less of the active germicide available for attacking microorganisms.

Chlorine and iodine disinfectants, in particular, are prone to such interaction. Alternatively, organic material can protect microorganisms from attack by acting as a physical barrier , The effects of inorganic contaminants on the sterilization process were studied during the s and s , These and other studies show the protection by inorganic contaminants of microorganisms to all sterilization processes results from occlusion in salt crystals , This further emphasizes the importance of meticulous cleaning of medical devices before any sterilization or disinfection procedure because both organic and inorganic soils are easily removed by washing Items must be exposed to the germicide for the appropriate minimum contact time.

Multiple investigators have demonstrated the effectiveness of low-level disinfectants against vegetative bacteria e. By law, all applicable label instructions on EPA-registered products must be followed. If the user selects exposure conditions that differ from those on the EPA-registered product label, the user assumes liability for any injuries resulting from off-label use and is potentially subject to enforcement action under the Federal Insecticide, Fungicide, and Rodenticide Act FIFRA.