By Siouxsie Wiles | Contributing writer to The Spinoff


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% in water. Or you could just use alcohol. Ethanol is best. Isopropyl alcohol is good too. Methanol is not as good but 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.