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ScienceMarch 7, 2020

How to get rid of Covid-19 from surfaces the right way

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While handwashing is a vital weapon in the battle against Covid-19, so is keeping surfaces clean and disinfected. Microbiologist Siouxsie Wiles on what you need to know about destroying coronaviruses around your home and workplace.

Read Dr Siouxsie Wiles’ other explainers on the Covid-19 outbreak here.

This week several more people in New Zealand have been confirmed to have contracted Covid-19, and the number of confirmed cases globally is approaching 100,000. We’ve been talking a lot about how this coronavirus is droplet spread so here’s the answers to a few questions people have been asking about that.

But before I get on to that, I just want to mention that a paper has just been published that shows that this coronavirus can be found on surfaces in hospital rooms where people with Covid-19 were being treated. The good news is that they also sampled the air and didn’t find the virus there – in other words, it’s not likely to be airborne. And the other good news is that they weren’t able to find the virus in those same rooms after they had been cleaned.

If someone is coughing and sneezing, how long can this virus last on surfaces? 

This is an excellent question. Given the SARS-CoV-2 coronavirus was only recently isolated, there aren’t any specific studies about this yet. But this has been investigated for other coronaviruses like the ones that cause SARS and MERS. Researchers in Germany have just published a paper in the Journal of Hospital Infection summarising all that data.

The upshot is that other coronaviruses can hang around on inanimate surfaces like steel for up to 48 hours, glass and wood for four to five days, and plastic for up to nine days.

How do we get rid of the virus on surfaces? 

So, the first thing to say is it will depend on the surface! But before we get in to the how, let’s start with the what. All the things that you frequently touch will be covered in your bacteria and unlikely to be much risk. The things we’ll be looking at keeping clean are things that other people can cough and sneeze on, or that lots of people touch. In a shared workspace this will be things like door and fridge handles, handrails, lift buttons, and switches. You get the picture.

The next question is whether things need to be cleaned or disinfected. If surfaces look visibly dirty, they should be cleaned first. Best to use a detergent which will have the added bonus of likely deactivating coronaviruses as they are enveloped viruses.

If you are using a disinfectant make sure it says it is antiviral and follow the instructions. Often, we just end up using a cloth to wipe the microbes around rather than actually letting them sit and stew in the disinfectant first so that it can do its job. Surfaces will need about 10 seconds soaking with the disinfectant for it to work.

Good disinfectants to look out for are things that contain hypochlorite (which is the main active ingredient in bleach) or activated hydrogen peroxide (0.5%). Others may contain benzalkonium chloride, though some studies have shown this is less effective against coronaviruses. You could also just use conventional bleach (at 0.1-0.2% available chlorine – check the back of your bottle) in water. Or you could just use alcohol. Ethanol is best. In New Zealand, methylated spirits is actually ethanol so you can use that. Isopropyl alcohol is good too. Methanol isn’t but is better than nothing.

Be mindful of what kind of surface you are disinfecting though. You don’t want to damage it! Please follow any instructions, and definitely don’t mix disinfectants together as you could end up with all sorts of dangerous chemical reactions happening.

Read Dr Siouxsie Wiles’ other explainers on the Covid-19 outbreak here.

What’s this Zoono stuff I’ve started hearing about?

Not one to look a gift horse in the mouth, Kiwi company Zoono, who make a range of antimicrobial products including wipes and hand sanitiser, announced that their “Z-71 Microbe Shield (…used in Zoono hand sanitiser) is > 99.99% effective against feline coronavirus”. With many pharmacies running out of hand sanitiser, their orders have gone through the roof.

Now I’ve a quick conflict of interest to declare here. I’ve just recently co-supervised a PhD student who has been looking at how effective Zoono is when used in a real-world situation. I can’t talk about that work for a variety of reasons, including that the PhD hasn’t been examined yet.

The technology behind Zoono’s products is pretty cool. The chemical cocktail bonds to surfaces forming a layer that is best imaged as rows and rows of pins. The idea is that any microbe that lands on the pins is burst and dies. The company sells products they claim will give you “germ free surfaces for up to 30 days”. Likewise, they also sell a hand sanitiser they claim will protect you all day.

Here comes the BUT…

I am not sure what evidence they have that their products will actually be that effective when people actually use them for real. Have they actually tested if the hand sanitiser stays on all day, even when people have been properly washing their hands several times a day? Have they actually tested if the surfaces really can stay “germ-free” when those surfaces aren’t in a lab but are in people’s actual homes and people are going about their actual lives in and around them?

One of the concerns I have when people rush to buy products like this is that they may end up with a false sense of security and think they are more protected than they actually are, and then end up doing things that put them at higher risk of infection.

In other words, don’t feel like you are putting your family at risk by not buying these products. There are plenty of cheaper options that we definitely know work in the real world.

Keep going!