Sanitising the city: does spraying the streets work against coronavirus?


Lisa Bricknell, CQUniversity Australia and Dale Trott, CQUniversity Australia

As the COVID-19 pandemic has grown, you will probably have seen photos and video of workers in protective gear using high-pressure sprays to sanitise city streets. Spain has even taken the radical step of spraying bleach on beaches. You may have asked yourself if this really makes much difference to the risk of coronavirus transmission. If not, why would governments expend time, energy and dollars doing it?

Based on our knowledge of the conditions required for disinfectants to work, we suspect these activities are as much about authorities being seen to do something as about actually stopping the spread of COVID-19.

The likely effectiveness of spraying streets and other public places depends on how the virus spreads, how the disinfectants work and what conditions these are used in.

How does the virus spread?

We now know the virus is spread mainly in two ways.

The first is through airborne droplets and aerosols that originate from infected individuals. The droplets are expelled into the air through a cough or sneeze and can infect another person who encounters them at close range. Droplets are larger and do not remain in the air for very long, quickly settling to the ground or another surface.

Aerosols are smaller and remain suspended for longer – up to three hours. Aerosols will rapidly dry out and disperse over time. This makes it less likely a person will be exposed to enough viral particles – known as the infectious dose – to be infected.




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The second way the disease is spread is via contamination of surfaces. When droplets settle, the virus can persist for varying periods, depending on the nature of the surface. For example, one study found the virus survives for up to 72 hours on plastic and stainless steel, 8 hours on copper and 4 hours on porous surfaces such as cardboard.

This experiment, however, was conducted under laboratory conditions indoors. So far, no information is available on how long the virus can survive outdoors. It’s also unknown how likely it is for you to become infected when you’re walking the city streets.




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How might disinfectant work?

We must also consider the process of disinfection. According to news reports, most authorities are using a diluted bleach solution to disinfect city areas. Research suggests the COVID-19 virus is susceptible to bleach, but it requires a contact time of about one minute to be effective.

Disinfectant is deactivated by a layer of organic matter on surfaces, including the same skin oils and sweat that leave fingerprints.
Shutterstock

Even if the disinfectant reaches every outdoor surface likely to be touched by people, including areas shielded from the spray, there is still a problem with using bleach in the typical conditions encountered outdoors. Sunlight and the build-up of organic matter on surfaces will rapidly deactivate the chlorine, the active ingredient in bleach. This means the disinfectant would probably become ineffective before the virus is killed.

For the virus to infect a person, it needs to enter the body. This can occur when your hands have become contaminated by touching a surface and you put your hands to your face, near your nose or mouth. But when was the last time you touched the ground and then touched your face without washing your hands?

The average person is rarely going to come into direct contact with city streets and footpaths with their hands. That’s another reason spraying these surfaces with disinfectant is unlikely to be an effective control measure.

Commonly touched surfaces such as handrails and road-crossing buttons are more likely sources of infection but would have to be cleaned before being sanitised with bleach. This is because organic matter builds up on frequently touched surfaces, including the natural oils on human skin. Even if cleaning were undertaken prior to sanitising, this process would need to be continuous as the next time an infected person touches the surface it can be recontaminated.

Spraying disinfectant into the air will have the effect of reducing the amount of virus that is suspended as aerosols. However, this will have a very limited effect as the disinfectant will rapidly disperse. Aerosols will be reintroduced the next time an infected person travels through the area.

Another consideration is that the droplets of bleach in the spray can be corrosive and cause harmful respiratory effects when inhaled. Spraying should only be done when there are no people around.

A far more effective regime is to recommend stringent personal hygiene. This includes regular hand washing with soap and water and the use of alcohol-based sanitiser when hand washing isn’t possible.

Why, then, are countries spraying streets?

So, if spraying disinfectant in urban areas is unlikely to be effective, why are we seeing some countries doing this?

Without being privy to the decision-making process, it’s hard to say. There are, however, a couple of possibilities. One is that the authorities want to create an environment that is free from COVID-19 but aren’t following the science. A more likely reason is to help people feel safe because they see authorities taking action.

In a crisis, people are less likely to take on board information that challenges their current beliefs. Although the science indicates urban disinfection is probably ineffective, it’s likely the general public believes otherwise. As a result, spraying city streets might have the effect of allaying fears and building trust in government and the messages it distributes.

A possible downside of this, however, is people who feel their environment is safe might be less stringent about personal hygiene and physical distancing. These precautions are vital in preventing the virus spreading through the community; if people stop observing these behaviours, the virus is likely to spread much more quickly.

The take-away message from this is that, while urban disinfection may increase public confidence, it is likely to be ineffective in protecting the public from infection.The Conversation

Lisa Bricknell, Senior Lecturer in Environmental Health, CQUniversity Australia and Dale Trott, Lecturer, Environmental Health, CQUniversity Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Can I get coronavirus from mail or package deliveries? Should I disinfect my phone?



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Euan Tovey, University of Sydney

According to Google Trends, the top two most searched terms about mobile phones this week in Australia were “how to disinfect phone” and “how to clean your phone.”

And the third most-searched “can I get coronavirus from…?”-style question in the past week in Australia was “can you get coronavirus from mail?” (If you were wondering, “can you get coronavirus from food?” was number one, followed by “can you get coronavirus twice?”)

In short, many Australians are wondering what role phones and mail and/or package deliveries may play in the risk of coronavirus transmission.

To better understand the risk, and what you can do to reduce it, it helps to think about how your phone or mail might come into contact with coronavirus – and what the evidence says about how long it lives on various surfaces.




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What do we know about how long the coronavirus can survive on a phone or mail?

Not a whole lot yet.

There has been some general media reporting on the role that surfaces play in the transmission of this coronavirus, termed SARS-CoV-2. That’s the disease that causes COVID-19.

But the main peer-reviewed journal paper on this topic was published about a week ago by the New England Journal of Medicine.

That paper found:

SARS-CoV-2 was more stable on plastic and stainless steel than on copper and cardboard, and viable virus was detected up to 72 hours after application to these surfaces.

It also noted:

On copper, no viable SARS-CoV-2 was measured after 4 hours […] On cardboard, no viable SARS-CoV-2 was measured after 24 hours.

These might be underestimates. The virus may survive even longer on these surfaces, depending on conditions. That’s because these studies looked at how long the virus would survive when in a “buffer” (a solution in which viruses live in the lab). In real life, they would be in mucous and would be more stable.

The fact that the viruses seemed to last longest on plastic is something of a worry and means that, on phones, the virus could potentially last for days.

It is important to remember this is a new virus and we don’t yet have all the data. New findings are emerging every day.

It’s also possible that, in reality, the virus may last longer on phones than indicated in the recent lab experiments.

CDC data published yesterday detected the faint genetic signature of viruses (viral RNA) which had survived 17 days on surfaces in cruise ships. That doesn’t mean infectious virus particles were found after 17 days – only a part of the virus was detected in this study – but it does suggest there may be some cause for concern regarding how long this coronavirus can last on surfaces. More research is required on this question.

Ideally, you should be cleaning your phones, tablets and keyboards with alcohol wipes – if you can get them.
Shutterstock



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How might virus particles end up on a phone?

Talking on the phone generates an invisible spray of airborne droplets. A person with COVID-19 can have a lot of virus in the mucous at the back of their throat, so they’re likely spraying the virus on their phone every time they make a call.

If an infected person hands their phone to someone else, the virus could transfer to the new person’s fingertips, and then into their body if they touch their mouth, eyes or nose. (And remember, not every infected person displays the classic symptoms of fever and cough, and may be infectious before symptoms show).

It’s also possible there is an oral-faecal route for transmission of coronavirus. This coronavirus is often detected in faeces.

That means, for example, that tiny particles of poo generated by flushing a toilet could settle on a toothbrush, on a phone brought into the bathroom or on surfaces/food in an adjoining room. They could then end up in your mouth. At the moment this has not been shown, but it is certainly possible. SARS was sometimes spread by this route.

That’s why frequent handwashing with soap is so crucial.

What about mail?

It is technically possible a package or mail coming to your house is contaminated with virus picked up somewhere along the way by people handling or coughing on it. I think, though, the infection risk is very low because, as the New England Journal of Medicine study found, the survival time on cardboard is thought to be around one day.

And unlike plastic surfaces, cardboard is porous. That means a droplet would probably penetrate into the material and may not be so easily picked up when you touch the package.

The survival time on cardboard is thought to be one day.
Shutterstock

What can I do to reduce my risk?

For starters, do the obvious things: wash hands frequently, reduce your contact with others (and if you do see other people, stay at least 1.5 metres apart, particularly if you are talking). Definitely don’t go out at all if you’re unwell.

Keep your phone to yourself. I’d be very reluctant to share my own phone with anyone right now, especially if they seem unwell.

It’s not clear what role children play in the transmission of this coronavirus but, just in case, children should be washing hands before they touch their parents’ phones. That said, it seems more likely at present that adults give it to children than the other way round.

Ideally, you should be cleaning your phones, tablets and keyboards with alcohol wipes (which need to be around 70% alcohol). They are quite effective at deactivating viruses (if somewhat hard to get now). Most baby wipes only have a low percentage of alcohol so are less effective but just the wiping would help remove virus particles.

In the worst case scenario, you can try using a damp cloth with a small amount of soap and water to clean your phone – but don’t let water get inside your phone and wreck it.

When it comes to mail and package deliveries, try to keep apart from the delivery person. Many delivery people are already forgoing the customary signature on the tablet, meaning you don’t have to touch a device or e-stylus that many others have already handled. You could consider wiping down a package before opening it, and washing your hands well after disposing of the packaging.

At the end of the day, the risk is never zero, and the world is a nightmare if you go too far down this route of worrying about every single surface.




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The Conversation


Euan Tovey, Associate Professor & Principal Research Fellow in Medicine, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.