How we know disinfectants should kill the COVID-19 coronavirus

The spread of the coronavirus disease COVID-19 has spurred a surge in sales of cleaning and disinfection products. The Centers for Disease Control and Prevention (CDC) recommends regular cleaning of frequently touched surfaces, along with thorough hand washing—both standard practices for helping slow the spread of viruses and bacteria. But consumers will be disappointed if they go looking for a product that specifically promises to kill SARS-CoV-2, the virus that causes COVID-19.

Although there’s good evidence the novel coronavirus is one of the easiest types of viruses to kill, scientists are still determining its exact nature and how big a role surface transmission plays in its spread. As researchers rush to understand the new pathogen, the US EPA is working to provide the public with information about disinfectants that can help slow its spread. Such claims won’t be allowed in brick-and-mortar stores, though, until more testing can be done.

Understanding exactly how a new virus spreads and persists in the environment takes time, resources, and virus samples for research—all of which are spread thin in the early weeks and months of an outbreak. That lack of data creates challenges both for people seeking advice about how to avoid this new disease, and the experts and organizations offering that advice.

“Everyone puts in a word of caution in there that we don’t really know, because we don’t have enough data yet,” says Charles Gerba, a microbiologist at the University of Arizona who studies how viruses spread in indoor environments.

On March 3, the EPA released a list of antimicrobial products for use against SARS-CoV-2, under an emerging viral pathogens program developed for just this kind of scenario. (The EPA regulates antimicrobial products as pesticides.) Under the program, which was introduced in 2016 and activated for the first time in January, makers of disinfectants can request approval to claim a product is expected to kill a particular virus based on its ability to kill similar viruses. Once an outbreak has been identified and the identity of the virus is confirmed by the CDC, approved products are temporarily permitted to distribute information about using the product for the emerging pathogen. The claim appears in a standard format such as: [Product name] has demonstrated effectiveness against viruses similar to SARS-CoV-2 on hard, nonporous surfaces. Therefore, [product name] can be used against SARS-CoV-2 when used in accordance with the directions for use.

According to the EPA, these statements are intended to “inform the public about the utility of these products against the emerging pathogen in the most expeditious manner.” The emerging pathogens program sidesteps the lengthy review process that is typically required for vetting disinfectant efficacy claims, which requires the establishment of a standardized protocol and testing with the actual virus or an EPA-approved surrogate. At this time, an EPA spokesperson says, no companies have sent the agency any efficacy data on the novel coronavirus or any surrogates.

Speed is of the essence, because surfaces such as doorknobs, countertops, and electronic equipment can transmit viral and bacterial diseases. According to the CDC, SARS-CoV-2 is believed to spread primarily person-to-person through airborne respiratory droplets. But it may be possible for the virus to spread on surfaces, too. Scientists know that similar respiratory viruses expelled into the air by coughing, breathing, or speaking can settle on surfaces, where they can linger in an active state for days, protected in a cozy covering of mucus. Although scientists aren’t sure yet how long the novel coronavirus remains active on a surface, one study done in a hospital found that similar coronaviruses can persist on hard surfaces like glass, metal, or plastic for up to 9 days (Journal of Hospital Infection 2020, DOI: 10.1016/j.jhin.2020.01.022). Another study, recently published on medRxiv and not yet peer reviewed, found that SARS-CoV-2 remains stable on plastic and stainless steel for 2–3 days. (MedRxiv 2020, DOI: 10.1101/2020.03.09.20033217). The authors also published their data in a correspondence in the New England Journal of Medicine (2020, DOI: 10.1056/NEJMc2004973).

During that time the virus can potentially be spread to anyone touching the surface, and to whatever they touch next. People tend to underestimate how quickly a virus can spread through a building and beyond via touched surfaces, Gerba says.

Gerba notes that technological advancements like large airliners, massive sports stadiums, and the proliferation of self-service kiosks have made it easier for diseases to spread rapidly. Mobile devices like smartphones can pick up germs from contaminated hands and then offload those germs later on to spread in a new location.

Enveloped viruses like SARS-CoV-2—which rely on a protective lipid coating—are the easiest type to deactivate. In contrast with many gastrointestinal viruses like norovirus which have a tough protein shell called a capsid, viruses with this fatty wrapping are relatively vulnerable.

“It’s much more sensitive. It’s sort of a wimpy protective shell,” says virologist Seema Lakdawala of the University of Pittsburgh.

There are a few ways to burst this flimsy shell. Alcohol-based products disintegrate the protective lipids. Quaternary ammonium disinfectants, commonly used in health-care and food-service industries, attack protein and lipid structures, thwarting the pathogen’s typical mode of infection. Bleach and other potent oxidizers swiftly break down a virus’s essential components.

The EPA’s list of disinfectants presumed effective against SARS-CoV-2 contains several dozen antimicrobial products including ready-to-use sprays, concentrates, and wipes. Each has been shown to be effective against at least one small or large nonenveloped virus, which are considered harder to kill than the enveloped variety. And that list is likely to grow; on March 9, the EPA announced it was expediting emerging pathogen-related requests that met certain requirements.

But consumers are unlikely to see such language on product labels any time soon. The EPA’s emerging viral pathogens program limits the places disinfectant makers can publish such a claim to off-label sources like websites, company help lines, and social media. Responding to public comments on an early draft of the program, the agency explained that this measure enables claims to be quickly removed if necessary. Product makers may also include the claims in technical literature distributed to health-care facilities, where it’s expected its recipients would have the background to put such claims in context.

The Clorox Company, which has several products on the EPA list, names three on its website’s coronavirus cleaning page along with the following statement: “Per the EPA Emerging Pathogen Policy, these products can be used against SARS-CoV-2 when used as directed.” The cleaning products giant has shared information about those products’ efficacy since late January, when the EPA activated its emerging viral pathogens program, according to a Clorox representative. The company’s standard practice is to seek pre-approval for the program when registering new products.

Of course, for the products to be effective, they should be used according to directions. The recommended contact time for common disinfectants ranges from 30 s to 10 min. Wiping them off too soon might clean the surface without disinfecting it, says Brian Sansoni of the American Cleaning Institute, a trade group for the cleaning products industry.

“Each disinfectant product—be it a spray or wipe, for instance—is formulated differently,” Sansoni says. Different products require different amounts of time to effectively kill a particular germ or virus.

Cleaning electronic devices like smartphones can be particularly challenging, with concerns about damaging sensitive components and coatings.

“Don’t use bleach,” Apple directs in recently released cleaning guidance for its products. The tech company says it’s safe to gently wipe keyboards and displays with a 70% isopropyl alcohol wipe or Clorox Disinfecting Wipes.

Gerba recommends disinfecting wipes for cleaning other surfaces, too. With spray-and-wipe products, consumers often wipe the product up before it can do its job. But in studies done in people’s homes, they are more likely to let a surface air-dry after swabbing it with the wipe, giving the disinfectant compounds time to work.

“Disinfecting wipes win hands-down,” he says.