How coronavirus is spread

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Infectious disease researchers at The University of Texas at Austin studying the novel coronavirus were able to identify how quickly the virus can spread, a factor that may help public health officials in their efforts at containment. They found that time between cases in a chain of transmission is less than a week and that more than 10% of patients are infected by somebody who has the virus but does not yet have symptoms.

In the paper in press with the journal Emerging Infectious Diseases, a team of scientists from the United States, France, China, and Hong Kong was able to calculate what’s called the serial interval of the virus. To measure serial interval, scientists look at the time it takes for symptoms to appear in two people with the virus: the person who infects another, and the infected second person.

Researchers found that the average serial interval for the novel coronavirus in China was approximately four days. This also is among the first studies to estimate the rate of asymptomatic transmission.

The speed of an epidemic depends on two things — how many people each case infects and how long it takes for infection between people to spread. The first quantity is called the reproduction number; the second is the serial interval. The short serial interval of COVID-19 means emerging outbreaks will grow quickly and could be difficult to stop, the researchers said.

“Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial interval of only a few days. Public health responders to Ebola outbreaks have much more time to identify and isolate cases before they infect others,” said Lauren Ancel Meyers, a professor of integrative biology at UT Austin. “The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat.”

Meyers and her team examined more than 450 infection case reports from 93 cities in China and found the strongest evidence yet that people without symptoms must be transmitting the virus, known as pre-symptomatic transmission. According to the paper, more than 1 in 10 infections were from people who had the virus but did not yet feel sick.

Previously, researchers had some uncertainty about asymptomatic transmission with the coronavirus. This new evidence could provide guidance to public health officials on how to contain the spread of the disease.

“This provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” Meyers said. “Asymptomatic transmission definitely makes containment more difficult.”

Meyers pointed out that with hundreds of new cases emerging around the world every day, the data may offer a different picture over time. Infection case reports are based on people’s memories of where they went and whom they had contact with. If health officials move quickly to isolate patients, that may also skew the data.

“Our findings are corroborated by instances of silent transmission and rising case counts in hundreds of cities worldwide,” Meyers said. “This tells us that COVID-19 outbreaks can be elusive and require extreme measures.”

Zhanwei Du of The University of Texas at Austin, Lin Wang of the Institut Pasteur in Paris, Xiaoke Xu of Dalian Minzu University, Ye Wu of Beijing Normal University and Benjamin J. Cowling of Hong Kong University also contributed to the research. Lauren Ancel Meyers holds the Denton A. Cooley Centennial Professorship in Zoology at The University of Texas at Austin.

The research was funded by the U.S. National Institutes of Health and the National Natural Science Foundation of China

Like many others, you probably have questions about the 2019 coronavirus. And one of those questions may have to do with how the virus is able to spread.

First, some brief explanation about the coronavirus itself: The clinical name for this novel coronavirus is actually SARS-CoV-2. It stands for severe acute respiratory syndrome coronavirus 2.

It originated from a family of other virusesTrusted Source that causes respiratory diseases like severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS).

Because the novel coronavirus is a new strain, it’s unfamiliar to our immune systems. And there’s not yet a vaccine for it.

Person-to-person spread

The virus is thought to spread mainly from person-to-person.

  • Between people who are in close contact with one another (within about 6 feet).
  • Respiratory droplets produced when an infected person coughs or sneezes.

These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.

Can someone spread the virus without being sick?

  • People are thought to be most contagious when they are most symptomatic (the sickest).
  • Some spread might be possible before people show symptoms; there have been reports of this occurring with this new coronavirus, but this is not thought to be the main way the virus spreads.

Spread from contact with contaminated surfaces or objects

It may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes, but this is not thought to be the main way the virus spreads.

How easily the virus spreads

How easily a virus spreads from person-to-person can vary. Some viruses are highly contagious (spread easily), like measles, while other viruses do not spread as easily. Another factor is whether the spread is sustained, spreading continually without stopping.

The virus that causes COVID-19 seems to be spreading easily and sustainably in the community (“community spread”) in some affected geographic areas.

Imagine sitting next to someone with a SARS-CoV-2 infection on the bus or in a meeting room. Suddenly, this person sneezes or coughs.

If they don’t cover their mouth and nose, they could potentially spray you with respiratory droplets from their nose or mouth. The droplets that land on you will likely contain the virus.

Or perhaps you meet someone who contracted the virus, and they touched their mouth or nose with their hand. When that person shakes your hand, they transfer some of the viruses to your hand.

If you then touch your mouth or nose without washing your hands first, you may accidentally give that virus an entry point into your own body.

One recent small study trusted Source suggested that the virus may also be present in feces and could contaminate places like toilet bowls and bathroom sinks. But the researchers noted the possibility of this being a mode of transmission needs more research.

Pregnancy and breastfeeding

Medical experts haven’t determined whether a woman can transmit SARS-CoV-2 in utero, through childbirth, or through her breast milk.

The CDC currently recommends trusted Sources that mothers with a confirmed case of the virus, as well as those who may have it, are temporarily separated from their newborns. This separation helps decrease the risk of transmission.

Women should speak with their healthcare providers about the benefits and risks of breastfeeding. The CDC hasn’t released any official guidelines regarding whether women with confirmed or suspected cases should avoid breastfeeding. They have, however, suggested that these women take the following precautionary measures trusted Source:

  • Wear a face mask while breastfeeding, if possible.
  • Properly wash their hands before holding or breastfeeding their infant.
  • Properly wash their hands before touching a bottle or breast pump.
  • Clean the breast pump each time it’s used.

They should also consider having someone who isn’t sick to use expressed breast milk to feed the infant.

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