Disinfectant Contact Time is Not Zero!

“Contact time,” as used by the EPA, is “the amount of time the surface should be treated for. The surface should be visibly wet for the duration of the contact time.” In practice, most people spray the countertop or others surface, wipe it off and go about their business, assuming that pathogens (aka germs) are killed on contact. It will come as a surprise to many that disinfectants simply do not work this way, and that EPA contact time is measured in minutes.

Disinfectants are “antimicrobial pesticides” regulated and defined by the EPA as “substances or mixtures of substances used to destroy or suppress the growth of harmful microorganisms such as bacteria,viruses, or fungi on inanimate objects and surfaces” as opposed to hand sanitizers, which are regulated by the FDA and intended only for use on skin. Any legally marketed disinfectant will display an EPA registration number on the product label that allows the user to access all related product information, including the required contact time, on the EPA pesticide registration website. “List N” identifies products registered for use against SARS-CoV-2, which causes COVID-19, our current pandemic affliction. This has direct implications for the spread of virus, since common practice does not reflect the need to keep the target surface wet for up to 10 minutes before contact. How many of us watch grocery cart handles being wiped or sprayed by store personnel and then offered for use with a total contact time of around five seconds?

If enforced, disinfectant contact time becomes a major chokepoint for venues that rely on frequent passthrough of riders or passengers (think amusement parks) while trying to do rapid wipe-downs or sprays between runs. Long-contact products will put the brakes on that.

The math also looks bad for voters, since the touch screens, knobs and other contact points on voting machines will require disinfection and a contact-time delay before the next voter steps up. Added to the already complicated logistics of long lines, social distancing and limited voting hours and stations, it is difficult to imagine tens of thousands of precinct personnel across the nation having the necessary and approved disinfectants and supplies and successfully enforcing both the cleaning and timing for every voter at every station.

There are thousands of disinfectants in the marketplace, and this list is not intended to promote or demote any of them. It is meant only to demonstrate the range of contact times and inform readers to consider contact time when selecting a product. Finding that number is usually not as simple as it should be, since labels tend to shout “Kills 99.9% of germs*” while burying contact time (if there at all) in very small print in the use instructions. The takeaway here is that disinfectants do not kill on contact, treated surfaces should not be considered “clean” until the prescribed contact time has expired, and that faster is better for most users. To borrow from a familiar idiom, it ain’t over until the disinfectant disrupts the viral outer lipid bilayer and disables its nucleocapsid proteins — and that takes time.

About the Author:

Scott Harris, PhD is the Associate Director of EHS Services in the Austin, TX office of GDS Associates, Inc. and an adjunct faculty at University of Texas at San Antonio, University of Utah and UNC-Chapel Hill. Dr. Harris received his PhD in Environmental Science, with a specialization in Disaster and Emergency Management, from Oklahoma State University and holds degrees in Public Health and Geology from Western Kentucky University.