More people are staying indoors to avoid contact with people potentially infected by Covid-19. But in light of a recent report from the US’s Centers for Disease Control and Prevention (CDC) that said RNA from the virus that causes Covid-19 was found in the Diamond Princess ship 17 days after its passengers had left, what are the risks of handling packages, groceries and what scientists call “high-touch” surfaces?

Does the cruise ship report imply that viruses survive up to 17 days on surfaces?

Dr Julia Marcus: A CDC investigation of the cruise ship found evidence of viral RNA in cabins that hadn’t yet been cleaned. But to be clear, that just means the virus was detectable – not that it was viable or that contact with those services would have been able to infect someone. (Editor’s note: RNA, or ribonucleic acid, carries the virus’s genetic information.)

Dr Akiko Iwasaki: It just means that there are parts of the virus that still remain. The virus needs many other components to be intact. If you have bits and pieces of RNA, that’s not going to make a virus, you need an entire intact genome. Just because you had a little piece of RNA doesn’t mean that there’s an infection.

How long can the virus survive on surfaces?

Marcus: The New England Journal of Medicine just published a study that tested how long the virus can remain stable on different kinds of surfaces within a controlled laboratory setting. They found that it was still detectable on copper for up to four hours, on cardboard for up to 24 hours, and on plastic and steel for up to 72 hours.

But it’s important to note that the amount of virus decreased rapidly over time on each of those surfaces. And so the risk of infection from touching them would probably decrease over time as well.

Could you become infected from just a single particle of coronavirus?

Iwasaki: There’s a certain amount of viral particle that you need to be exposed to become infected. If you just had one viral particle on your finger, it’s unlikely that you’re going to be infected. Some viruses are very potent, you only need like 10 particles to get infected, while others you [may] need millions. The fewer viral particles you’re exposed to, the less likely you’re going to get infected. That’s why the amount of virus on a surface is important.

How many people are being contaminated via surfaces as opposed to airborne particles or direct contact with an infected person?

Marcus: As far as we know right now, people are much more likely to be infected by close contact with an infected person than by touching a contaminated surface. That said, it’s still important to be conscious of what we’re touching, especially high-touch surfaces, and be careful about cleaning our hands after touching things. For example, public transit or grocery stores and places where there tend to be a lot of people.

Iwasaki: The virus is pretty stable on [materials] like plastic and steel – they can persist for a few days. So it’s very possible that someone who’s sick will deposit the virus on to the surface and then somebody else will touch it and touch their face.

Is there a risk of being infected by groceries and packages that we have delivered?

Marcus: It’s a low risk, but it’s possible that if someone is delivering a package to your house and they are sick, that may be a route for transmission. I would recommend that any time something new comes into your household, be conscious of washing your hands after handling it.

Iwasaki: The [virus’s] stability is pretty good on the cardboard. Once you get those packages, open them, quickly throw away the cardboard, wash your hands, and try to avoid touching your face. Take any measures that you can to minimize contact from the surface of the package to your face.

Is it possible the contents of a package could have been contaminated by whoever packed it?

Iwasaki: There’s definitely a possibility of contamination, but it’s much more likely that the outer cardboard itself will come into contact with a lot more people than what’s inside. And if it takes days to get to your home, whatever virus that was inside will be deactivated already.

Do you have any tips for cleaning surfaces?

Marcus: It’s good to routinely clean any high-touch surfaces, like door handles and toilets. Regular household cleaners are effective, including bleach solutions and alcohol solutions of at least 70% alcohol. If somebody in your household has been diagnosed with Covid-19, then cleaning and disinfection becomes much more important and should be done more frequently.

Iwasaki: The [Food and Drug Administration] has a list of home cleaning products that are known to kill Covid-19. This virus is an enveloped virus so it doesn’t survive well in soap and alcohol.

Experts:

Dr Akiko Iwasaki, professor of immunology at Yale University