How long can the new coronavirus live on a surface, like say, a door handle, after someone infected touches it with dirty fingers? A study out this week finds that the virus can survive on hard surfaces such as plastic and stainless steel for up to 72 hours and on cardboard for up to 24 hours.
"This virus has the capability for remaining viable for days," says study author, James Lloyd-Smith, an assistant professor of ecology and evolutionary biology at the University of California, Los Angeles, who researches how pathogens emerge.
Although the World Health Organization had previously estimated the survival time on surfaces to be a "few hours to a few days" based on research on other coronaviruses, this is the first study by scientists at a federal laboratory to test the actual virus causing the current pandemic, SARS-CoV-2.
The study is out in preprint form and expected to be published.
Interestingly, some surfaces are less hospitable to SARS-CoV-2. For instance, the virus remained viable on copper for only about four hours.
It's useful to know how long it can stay alive of course, because the virus can contaminate surfaces when an infected person sneezes or coughs. Virus-laden respiratory droplets can land on doorknobs, elevator buttons, handrails or countertops — and spread the virus to anyone who then touches these surfaces.
To test the survival time of the virus, scientists at the Rocky Mountain Laboratories in Montana, part of the National Institutes of Health, conducted a series of experiments comparing the novel coronavirus with the SARS virus (a similar coronavirus that led to an outbreak back in 2003).
In the lab, "they'd pick up the virus from the surfaces that had been contaminated and then put [the virus] into cell cultures," he explains. Then the researchers documented whether the virus could infect those cells in the dish. They did this multiple times, for both the viruses, at various time points.
"Big picture, the [two viruses] look very similar to each other in terms of their stability in these environments," Lloyd-Smith says.
Lloyd-Smith says these findings establish a good ballpark estimate for the survivability of the virus on these surfaces. "In a laboratory experiment, the conditions are pretty carefully controlled and constant," he says. By comparison, "in the real world, conditions fluctuate" — conditions like temperature, humidity and light. So the survivability may vary, too.
For instance, if the virus contaminates a sunny windowsill or countertop, it may not last as long.
"Ultraviolet light can be a really powerful disinfectant and we get a lot of UVA light from the sun," says Daniel Kuritzkes an infectious disease expert at Brigham and Women's Hospital. "Direct sunlight can help rapidly diminish infectivity of viruses on surfaces," he says. He was not involved in the new research.
Much is still unknown about the virus's survivability on other types of surfaces like clothing, or carpeting. Kuritzkes says that based on prior research, it seems that "flat surfaces and hard surfaces are more friendly to viruses than cloth or rough surfaces."
And how about food? "Food is probably not a major risk factor here," Kuritzkes says. That's because most infection from the new coronavirus starts with the respiratory system, not the digestive tract. So infection comes from getting the virus on your hands and then touching your own eyes, nose and mouth. "Of more concern would be utensils, and plates and cups that might be handled by a large number of people in a cafeteria setting, for example," he says.
So, what can you do to protect yourself? Well, you've likely already heard this. Wash your hands. And wipe down shared surfaces.
Follow these tips for cleaning surfaces — your own and public ones.
Wipe right: Use ammonia or alcohol-based products. Skip the baby wipes
"The good thing about COVID-19 is that it does not require any unique cleaning chemicals to disinfect hands and surfaces," says Andrew Janowski, an infectious disease expert at Washington University School of Medicine and St. Louis Children's Hospital. COVID-19 is the disease caused by the current coronavirus.
Good old-fashioned soap and water does the trick.
You can also use a wipe, but make sure you use an alcohol-based wipe, not baby wipes, which may not be effective, Janowski says.
And given that wipes are hard to come by at many stores at the moment, you can instead buy an EPA-registered disinfecting spray, such as one on this list from the Center for Biocide Chemistries, recommended by the Centers for Disease Control and Prevention and by Dr. David Warren, an infectious disease specialist at Washington University School of Medicine in St. Louis.
Or make a bleach-based spray yourself. You can make a DIY cleaning spray by mixing 4 teaspoons bleach per quart of water, according to the CDC.
Wash. Your. Hands. (Seriously!)
Yes, you've heard it a hundred times. So do it, already! Especially after you've been out in public, touching a lot of surfaces. Lather up with soap and scrub for 20 seconds. (Two times the "Happy Birthday" song, or sing "Baby Shark" — you'll get midway through Daddy Shark).
And be thorough. Spend some time rubbing the backs of your hands as well as the front, interlace your fingers and pull them through, soap up each thumb with the opposite hand and, finally, to keep your fingernails virus-free, lightly scratch them against your palm. (For more detail, listen to NPR Short Wave's Maddie Sofia give a lesson here.)
Hand-washing is so important that if everyone followed good hand-washing hygiene, it could prevent an estimated 1 in 5 respiratory infections, according to the CDC — that's the equivalent of about 6 million cases of the flu this year.
Hand sanitizer: DIY in a pinch?
Hand sanitizer is effective at killing viruses, too, although hand-washing is preferred, according to the CDC. If you can't get to a sink, hand sanitizer is a good backup plan — just make sure it's at least 60% alcohol.
Given the shortage of hand sanitizers in some stores and reports of price-gouging online, there's lots of interest in DIY hand sanitizer. We've seen lots of recipes calling for a combination of rubbing alcohol and aloe vera gel, like this one from Wired.
"On paper, if a recipe can maintain the alcohol concentration above 60%, it should be effective against SARS-COV-2," says Janowski, but he says getting it just right might be trickier than you think. If in doubt when making these homemade sanitizers, soap and water are still effective against the virus.
Your smartphone is like a third hand. Wipe it down
So you've just washed your hands and you're feeling squeaky clean. Then you pick up your cellphone, and guess what? It's covered with potential pathogens.
"Studies have shown that smartphones surfaces are covered in bacteria, including bacteria that can cause serious infections like Staphylococcus species," says Judy Guzman-Cottrill, an infectious disease expert at Oregon Health & Science University.
And phones are often held close to the eyes, nose and mouth, where germs can enter the body. So wipe it down often.
And you don't have to rub down your phone for long if you're using an alcohol-based sanitizer. "Just a few seconds should be sufficient to disinfect," says Janowski.
Try this stinky trick to stop touching your face
Your face offers multiple entry points for the virus. So every time you touch your eyes, nose and mouth with grubby hands, you risk infection.
"If you have touched a table or a doorknob or some surface contaminated [with the virus] and then touch your eyes, nose or mouth, you have a chance of inoculating yourself with the virus," Kuritzkes says.
But, as a matter of habit, most of us touch our faces multiple times an hour without even realizing it.
So, here's an idea. "After you wash your hands really well, touch a piece of raw onion," says Catherine Belling of Northwestern University Feinberg School of Medicine. With this strong smell on your fingers, "you'll notice when you touch your face," she says. Sure, it may make you a tad antisocial, but it could be a good way to train yourself to touch less.