Coronavirus (COVID-19) is a highly contagious disease. The severe acute respiratory syndrome (known scientifically as SARS-CoV-2) that causes COVID-19 can pass easily from infected people to healthy people. Although it’s a new virus, it has spread to almost every country in the world in a very short space of time.
But how does disease transmission of coronavirus actually work? We take a look at all the ways infected people can spread the virus.
How we measure the spread of COVID-19
When governments and healthcare experts have to contain a disease outbreak, such as coronavirus, they need to understand how contagious it is. They need to consider how far and how quickly the virus can spread so they can take containment measures.
One of the measurements that epidemiologists look at is called R0 (pronounced R-zero). The idea is that an average infected person, in a susceptible population with no immunity, has to infect at least one other person for a disease to spread. The R0 must be higher than one to cause a contagious outbreak.
The novel coronavirus has an R0 of between 2 and 2.5. Each COVID-19-infected person infects an average of 2.25 other people. For comparison, seasonal influenza has an R0 of 1.28, which is quite low. Measles has a high R0 of between 12 and 18.
The R0 level means COVID-19 is more contagious than flu but considerably less than measles. The reason for concern is how quickly it has spread globally and the relatively high death rate.
Thankfully, R0 isn't fixed. When people use the correct preventive measures to stop or slow the spread, the R0 decreases.
An essential step to decreasing the COVID-19 R0 is to understand how you can become infected, then act accordingly. Here’s how the virus can spread from infected to healthy people:
The primary route of COVID-19 transmission is through person-to-person contact, according to the US Centers for Disease Control and Prevention (CDC).
When an infected person coughs or sneezes, without using their hand or a tissue to cover their mouths, they release millions of SARS-CoV-2 laden droplets into the air. These droplets land on your skin and clothes, or you breathe them in, giving the virus a doorway into your body.
You may not realise it, but you touch your face all the time. The average person touches their face around 23 times an hour, and almost half of those touches involve a mucous membrane. If an infected person touches their nose or mouth, they can readily pass the virus onto other parts of their skin or clothing.
If you shake hands with, hug, kiss or in any other way touch an infected person, you could find that the virus passes to you as you touch your face. Once on your face, the virus can enter your body through the nose and mouth.
Germs of all types spread quickly on surfaces. Tables, desks, door handles, coffee machines; in fact, any surface than an infected person touches can become a vector for coronavirus.
When someone infected with COVID-19 coughs, sneezes or touches a runny nose, the virus contaminates their hands. Every object they touch is now a new breeding ground for the virus.
When a healthy person touches the viral-laden surface, the virus transfers to their hands. They can now spread the virus on their hands to other surfaces, including their face.
It might seem unlikely that a virus could spread effectively from surfaces, but research shows the opposite. Scientists from the American Society for Microbiology demonstrated that inside two to four hours, a harmless virus placed on a doorknob or tabletop in an office could be detected on 40% to 60% of workers, visitors and other surfaces.
Poor hygiene contributes to the spread of viruses on high-touch surfaces. This is why regular and proper hand washing is vital.
How long can coronavirus survive on surfaces?
While transmission of SARS-CoV-2 to people from surfaces has not yet been documented, evidence suggests it may remain viable for hours to days on surfaces made from a variety of materials, according to the Centre for Disease Control and Prevention (CDC).
When a disease passes from person to person because infected poo enters a healthy person’s mouth, this is called the faecal-oral route of transmission.
Although this sounds absolutely horrifying, it’s a common route of infection for many diseases. It doesn’t mean that you need to consume faeces, like a dung beetle, it refers to how faecal material from an infected person can transfer to surfaces due to poor hygiene or from flies. A healthy person can then eat food that has touched the contaminated surfaces, hence faecal-oral transmission.
This route of transmission is extremely an extremely common way to contract food poisoning. Researchers are not entirely certain if the faecal-oral route can transmit SARS-CoV-2.
Studies have shown that there is evidence of coronavirus in patients’ faecal samples. In fact, some patients have positive faecal samples long after their respiratory samples become negative.
When faeces carry a pathogen, like SARS-CoV-2, it can contaminate toilet bowls, sinks, bathroom surfaces and anywhere the person touches if they have not washed their hands correctly.
There exists the possibility that asymptomatic people with COVID-19 could spread the virus through the faecal-oral route of transmission. Further research is called for, but once again, this information highlights the need for good hygiene practices.
What about pregnancy and breastfeeding?
Experts do not yet know if a mother can transmit coronavirus to their baby while it’s in the womb, during birth or through breast milk.
One study from China looked at 38 pregnant women with COVID-19. They found that all neonatal specimens, including placentas, were negative for the disease.
The advice from the CDC is that mothers with confirmed COVID-19 should separate themselves from newborn babies to decrease transmission risk and follow the CDC advice on breastfeeding.
Can you catch coronavirus from food?
Is that pizza delivery safe? The US Food and Drug Administration (FDA) says there is "currently there is no evidence of food or food packaging being associated with transmission of COVID-19." SARS-CoV-2 cannot survive for extended periods on surfaces. The level of virus decreases over time, unlike bacteria that can multiply on surfaces, including food.
Supermarket food, or delivery food, comes in a package of some sort. That packaging material is a surface that, technically, could be infected with COVID-19 if an infected person sneezed or coughed onto it. It is, therefore, a good idea to wash your hands if you’ve been handling food packaging from an outside source. Even in more normal times, the food we eat is produced to a high standard that aims to eliminate food-borne pathogens.
People who work in the food industry are trained and aware of good practices for food safety. Most food we eat is cooked in some way. The cooking process for most food would kill the virus. Plus, the stomach is extremely acidic, so if a virus made its way there on the food you eat, it’s unlikely to survive.
Can you catch coronavirus from blood?
Many diseases can be spread through blood and blood products. Thankfully, in common with other respiratory diseases, COVID-19 does not seem to be one of them.
There have been no reported cases of blood transfusion-transmitted coronavirus. Researchers and medical teams are now considering using plasma extracted from the blood of COVID-19 survivors to treat current patients.
The take-home message:
Researchers still have much to learn about COVID-19 and how it is transmitted.
The best advice, for now, is to carry out good hygiene practices, including proper hand washing.
The information in this story is accurate as of the publication date. While we are attempting to keep our content as up-to-date as possible, the situation surrounding the coronavirus pandemic continues to develop rapidly, so it's possible that some information and recommendations may have changed since publishing. For any concerns and latest advice, visit the World Health Organisation. If you're in the UK, the National Health Service can also provide useful information and support, while US users can contact the Center for Disease Control and Prevention.
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