New article: coronavirus lingers on surfaces longer than we thought

October 14, 2020 • 9:45 am

While most cases of Covid-19 are surely contracted via interperson contact (hugging, respiratory droplets, talking next to someone, handshakes, and so on), this new article from Virology Journal, produced by five Australian researchers, suggests that the virus can linger on various surfaces substantially longer than we suspected, and those infection-bearing surfaces (called “fomites”) can carry a viral load large enough to cause infection. Remember when you thought that paper and cardboard could be “disinfected” by leaving it untouched for 24 hours, so that the virus would all die? That doesn’t seem to be the case, at least according to this paper.

Click below to read the screenshot; the pdf is here , and the reference is at the bottom.

The results can be conveyed briefly. The researchers inoculated live virus onto six types of surfaces that might be encountered by people on a daily basis: Stainless steel (cookware, etc.), polymer currency (used in Australia), paper currency (no longer used in Australia but used in many other places), a glass surface (cellphones, touchscreens, etc.), vinyl, and cotton fabric.  The materials were incubated at three temperatures (20, 30, and 40 Celsius, corresponding respectively to 68, 86, and 104 degrees Fahrenheit, respectively), and incubation was in the dark, as UV light kills the virus more quickly (hint, put your envelopes and packages in the light when disinfecting them).  The relative humidity was 50%, though higher humidity also decreases viral survival.

The virus titer is said by the researchers to “represent a plausible amount of virus that may be deposited on a surface”. Samples were taken over 28 days, and the amount of living (i.e., infectious) virus measured by standard methods.

The attrition of the virus due to death over time was measured in three ways: the D value (time at which only 10% of the original sample remained), the half life (time at which half the original sample remained), and Z values (the increase in temperature required to reduce the D value by 90%, in other words to kill 99% of the inoculate).

The table below tells you everything you need to know: the D values and half lives (latter in parentheses) for all six materials at three temperatures, as well as the Z values:

Now what we don’t know about these values, and what is really important, is how much virus has to remain on the surface before it loses its ability to infect you (remember, probability of getting infected is proportional to the amount of virus you pick up and transfer to your nose, mouth, or eyes). This isn’t discussed in the paper, but I’d say a reasonable precaution is the D value: 90% loss of titer.  Perhaps readers in the know can tell us after they’ve read the paper.

But even if you use the half life, at 20°C, two days is a minimum for any surface save cotton (1.7 days). Paper loses half its virus load in three days, and glass in two. But remember, this is in the dark, and half-lives will be shorter in sunlight. Half-lives and Z values decrease dramatically at higher temperatures, though I think 20°C is what we should pay attention to because it’s close to room temperature.  If 10% of the original titer is not enough to infect you, you’ll have to wait 10 days for paper and 6 days for glass. Surprisingly, cotton cloth was the material that retained viable virus for the shortest amount of time.

The Z values show that an increase in temperature of about 15°C is enough to kill 99% of the virus existing at a given temperature.

The researchers also found that except for cotton, viable virus was still found on all surfaces after 28 days.

What’s the lesson for us? Well I can’t say (nor do I wish to purvey public-health advice!), because the crucial information—the amount of virus normally deposited on a surface, and how much of that must remain to give you an appreciable chance of getting infected if you pick it up—is missing. What the authors conclude is this:

The data presented in this study demonstrates that infectious SARS-CoV-2 can be recovered from non-porous surfaces for at least 28 days at ambient temperature and humidity (20 °C and 50% RH). Increasing the temperature while maintaining humidity drastically reduced the survivability of the virus to as little as 24 h at 40 °C. The persistence of SARS-CoV-2 demonstrated in this study is pertinent to the public health and transport sectors. This data should be considered in strategies designed to mitigate the risk of fomite transmission during the current pandemic response.

I guess we’ll have to leave it to the “considerers”, i.e., medical researchers and public health experts, to translate these results into recommended behaviors. But I think it’s smart to disinfect paper for two days instead of one after getting it, and use as little currency as possible (currency is like a circulating Petri dish, carrying E. coli as well as coronavirus. Use your credit card instead, and wipe it off with ethanol or wash it with soap and water after you use it. Put it in the machine, and don’t hand it to anyone unless you have to. Oh, and don’t let anybody use your cellphone.


Riddell, S., Goldie, S., Hill, A. et al. The effect of temperature on persistence of SARS-CoV-2 on common surfacesVirol J 17, 145 (2020).

42 thoughts on “New article: coronavirus lingers on surfaces longer than we thought

  1. This paper has been criticised in the virology community because of the dark conditions of the experiment (accurately described by our host as you would expect, but less so in the wider press). This is because UV inactivation is usually one of the most important ways that viruses bite the dust so it’s not clear how applicable the results are in the real world.

    Note, I am not a virologist, although I know a few.

    1. I can see the problem, but contact transmission would likely happen inside buildings where there is not much UV.

  2. After spending four months in Massachusetts, where I spent a lot of time outdoors, I am back in Florida where the temperature and humidity is high and the sunlight is intense, I should worry less about lingering virus load on surfaces.

    We continue to wear masks, wash hands thoroughly and use antiseptic.

    The most annoying aspect of driving for two days was that most of the rest areas had air blowers for drying hands which I will not use, so I had to shake my hands dry after washing.

      1. Or, if you are a COVID denialist, you can just close your eyes, knowing that if you can’t see the virus, it can’t see you.

  3. Also an interesting article in the WP yesterday concerning how far behind we are in this country with sequencing the genomes of the virus. Other countries are way ahead of us in this regard. Considering our anti science chief it is not surprising.

  4. The relevant question is whether there is evidence for fomite transmission, that is, cases where a susceptible host has acquired infection from being in an environment where an infected host had been previously. My understanding is that there isn’t much.

  5. Speaking of cell phones, my wife ordered an interesting gizmo called “Phone Soap.” It’s a container you put your phone in, and it baths it in UV light for a few minutes. We use it whenever we use our phones out and about.

  6. … use as little currency as possible (currency is like a circulating Petri dish, carrying E. coli as well as coronavirus[)].

    That sucks, since I’ve always been a gangster roll kinda guy. Except for a few bouts of serious impecuniousness, I’ve always been that way, from the time I fist started making money of my own as an adolescent. I like the comfort of starting the day with a wad of cash in a clip in my pocket, since you never know what kind of needs and opportunities might arise in the course of a day, some of them involving folks who don’t take plastic.

    Maybe now, for health reasons, I’ll go back to keeping the larger, cleaner, less circulated bills on the outside of the roll again (a habit I broke after discovering I’d accidentally dropped a pair of C-notes in the cup of a busker, thinking they were ones. After that incident, the busker always gave me a big smile every time I walked by.)

    1. “[S]ince you never know what kind of needs and opportunities might arise in the course of a day, some of them involving folks who don’t take plastic.” – I wondered where you were going with that until you mentioned the busker, Ken! (And no wonder he always gave you a smile after your unintended generosity.)

      1. When I lived in the Village in NY there was a beggar who sat at every day at his fixed spot at the bottom of the stairs leading to the Subway, and I sometimes droped a few coins in his bag. One day I went to my bank and there he was in front of me in the line, depositing the content of his bag into his account.

    2. I can’t remember when I last used actual hard cash to pay for something. In the UK, cash was already going the way of the dodo before the pandemic, but now I think this is its K-T boundary event.

      1. t has definitely accelerated the dominance of digital media over physical media. Films, TV shows, albums, games in particular: I haven’t bought a blu-ray or DVD/CD in ages.

        With gaming in particular there’s a big incentive for me to buy physical copies because they’re both considerably cheaper than digital and you can part-exhange them once you’ve finished them. But COVID might have sounded the death knell for that way of playing and owning games.

      1. My sons, when they were teenagers and I’d reach in my pocket to pick up a tab, used to say, “Check out Dad, big-ballin’.” Usually right before they hit me up for “an inside bill.” 🙂

    3. I have always preferred cash, but have not used it since March. I don’t even carry any in my pocket. The best part of credit cards these days is the technology that let’s you just tap the card on the reader instead of sliding it or inserting it. I have been taking some Clorox wipes with me when I go shopping and if I have to enter numbers on a key pad, I do it with the wipe and not my fingers. I almost always give something to buskers (as I have done a bit of busking myself, usually on St. Patrick’s day), but I have not seen anyone doing so since this all started.

      1. I have always been a cash kind of person, as it makes tracking my finances easier (really, for me. Fixed wad each week for groceries, fuel, and so on, and I keep good track so I don’t run tight).

        For many things, I have been using the plastic more, and as policy I give NO other personal information (or, on line, name and cards info), yet I get emails, paper mail, telephone calls, and so on, following card transactions, often from direct competitors of whom I made purchase from, I suspect that the bank is selling the information, despite regulations prohibiting it, my explicit order, and the banks written policy.

        If I keep my wallet in my pocket (30 to 35C) the half life for US notes will be about a day. I go out once a week. Add that the humidity/moisture level is a bit higher in the wallet than the environment as a whole, and that there is no consideration of the difference between viable virus and the ease of transmission from the surface, I don’t know that there is much concern, other than in the case of the busker or an ecdysiast.

  7. The idea of taking the train to visit my elderly mum at Christmas is looking more and more like a no-go. Other than pretending to be an orthodox Jew and sitting in one of those clear plastic bags for the whole journey I can’t see any way to do it safely.

    BTW, and I’m being half-serious here, but if an increase in temperature as outlined in the chart kills 99% of the virus couldn’t you just set up some kind of mild-heating-disinfectant chamber at your door? Like an easy-bake oven? Stick your shopping in there, wait for the ding, then retrieve it. I’m excluding stuff like chocolates, yoghurts, giant ice swans, new pet hamsters, etc. but for the rest of your stuff?

    1. I’m getting on a plane tomorrow for the first time since the pandemic hit. My aunt and godmother — the matriarch regnant of the whole huge Irish-Catholic clan on my maternal side — died a couple days ago at age 92. (She was trying her best to hang on so she could vote Biden, but came up just short.)

      I’m reluctant to travel, but this is one where I’ve gotta go pay my respects, the ‘Rona be damned.

        1. Yes, that is good advice, an N95 not just protects others from you, but gives reasonably good personal protection.
          I think the airplane itself, with it’s high turnover aircon is relatively safe, but I doubt the same can be said of the airports.

          1. Don’t get carried away with the N95 cultism; they are not created equally.

            Note that some portion of them — all called N95 — have a free-flowing exhaust valve.

            Excellent for the construction trades, but making them useless towards others.

  8. I’m not sure about this, the dark conditions apply to your gangster roll and the cellphone in your pocket, but then the temperature in your pocket is higher than 20°C, and probably closer to 30°C.
    Anecdotal observation: with masks (I was an early proponent), social distancing and sanitising hands ad nauseam (yes, especially after touching cash), I did not have a cold since February. A whole winter without a cold, that is unusual. Normally I would have had at least 3! Maybe these measure do work?,

    1. No sicknesses at all since February (I do think I may have already had COVID, but I’ve been tested twice negative (but not for antibodies).

      There is no doubt that PPE helps. Just look to K-12 kids…they are much less sick than in previous years.

  9. Gloves can help a lot, not just for protection but reminders as well. When I wear gloves at work I am reminded to wash my hands when I take them off before touching my keyboard or eating. I also wash the gloves I use periodically. Also gloves would be useful if I carried COVID, since I would be less likely to contaminate surfaces at work.

    1. How exactly would gloves lower the contamination of surfaces?

      As far as I know (not being an expert but following many of their interviews and publications), gloves are often said to be contraproductive against SARS-CoV-2.

      o The virus may actually live longer on them because of their smooth surface and lack of the acidic environment of our skin.

      o They may give people a false sense of security, so they neglect other measures like cleaning their hands (or gloves).

      o Prolonged use may damage the skin, thus making it vulnerable to other germs or health issues.

      The CDC also doesn’t recommend them for everyday usage:

      This article goes into more details and cites some medical professionals:

  10. Here in NZ coming out of winter we’ve had low hospital admissions and cases for respiratory and flu type diseases.
    Higher vaccination uptake, lower contact in conducting daily business, safe distancing, mask-wearing, hand washing, cleaning surfaces or avoidance (don’t touch handrails in public areas) all of the above helping, and as you would expect some more than others.
    Just as well as we have been going hell for leather on testing, NZ MoH do sequencing as part of the control measures.. so that must take up a lot of lab time.
    Things are as normal as possible at the moment.

  11. “I think 20°C is what we should pay attention to because it’s close to room temperature.  If 10% of the original titer is NOT enough to infect you, you’ll have to wait 10 days for paper and 6 days for glass.” (Isn’t the “not” a typo here?)

  12. Doing the experiment in the dark made it useless. It is irrelevant to the real world.

    Rickflick above suggested that there is not much UV indoors, in offices, shops, and such. Fine. Then do the experiment in office light. Or better, outdoors, in office light, AND in total darkness.

    I seriously suspect the biases of the experimenters.

  13. I generally prefer cash but I’ve always washed my hands after going outside or touching money b/c the professor is right – it is filthy stuff at the best of times. In fact you can almost tell a country’s level of development/wealth by the filth of its currency. Japanese yen are almost always spotless and crisp like little banknotes going to the opera in a tuxedo, but go to Egypt or Bangladesh and the damp, stinky, grimy money turns your stomach.
    In the US our greenbacks aren’t bad but we’re no Japan.
    My birthplace Australia has polymer notes which are excellent (and apparently, cleaner). They make a bundle producing polymer bills for dozens of countries.

    I’m not a big fan of the cashless society though – cash is one of the last bastions of pure privacy we have and if you have, ummm… hobbies… that aren’t socially or legally acceptable it can be the only way to pay.
    Some countries like Sweden have gone almost completely non-cash, even panhandlers accept e-pay.

    D.A., NYC

    1. Filthy lucre?! 😸 become a money launderer! I quite agree about cash but not because of.. hobbies! ( Go to Oregon I am told). Privacy & too many people watching others if only for the purpose of selling you stuff, is at risk. But we could do more to protect that privacy, & we absolutely should.

  14. I think – what do I know? – that this is irrelevant. It was pretty clearly stated by most authorities that most transmission is aerosol rather than by touch. If you maintain social distance, & avoid crowded places when not wearing a mask, you cut your chances of infection a lot. They should have done the same experiment in real life situations.

    The virus is not a problem in laboratory conditions!

    Just do not touch your face when out, & wash hands.

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