Coronavirus carriers can transmit it without symptoms: what you need to know


  • The coronavirus infected more than a million people worldwide in three months. Scientists rush to find out how it spreads so quickly.
  • According to the director of the CDC, 1 in 4 people can be asymptomatic carrier – a contagious person but not physically ill.
  • These carriers are thought to play an important role in the spread of the virus and are the reason why the general American public will probably be invited to start wearing face masks.
  • Visit the Business Insider home page for more stories.

At least a third of the world is subject to some type of foreclosure as a result of the coronavirus pandemic, while governments encourage social distancing to curb the spread of the virus.

This is because the COVID-19 virus is insidious.

“There is significant transmission from people with no symptoms,” Stephen Morse, epidemiologist at Columbia University, told Business Insider.

According to Robert Redfield, director of the Centers for Disease Control and Prevention, 25% of people infected with the new coronavirus have no symptoms or get sick, but they can still spread the disease to others.

” A die [pieces of] The information we have pretty much confirmed today is that a significant number of those infected remain in fact asymptomatic, “Redfield told NPR on Tuesday.

These asymptomatic carriers, Redfield added, are likely to contribute to the rapid spread of the coronavirus worldwide and make it difficult for experts to assess the true extent of the pandemic.

“We do not know all the unidentified cases. It is mostly hospital patients who are listed, “said Morse.

The prevalence of asymptomatic transmission does not bode well for global containment efforts, as Bill Gates recently wrote in an article published in the New England Journal of Medicine.

“This means that COVID-19 will be much more difficult to contain than Middle East respiratory syndrome or Severe Acute Respiratory Syndrome (SARS), which has been spread much less effectively and only by symptomatic people,” said Gates.

What we know about asymptomatic and presymptomatic transmission

coronavirus in Wuhan

A worker takes the temperature of a customer at the entrance to a Walmart store in Wuhan on January 27, 2020.

Photo AP / Arek Rata

The first confirmation that the coronavirus could be transmitted by asymptomatic people came in February, when a case study described a 20-year-old woman from Wuhan, China, who transmitted the coronavirus to five family members but no has never been physically ill herself.

A report by the World Health Organization on the coronavirus epidemic in China, published in February, found very few cases in which a person tested positive has never had symptoms. Instead, the majority of asymptomatic people at the time of diagnosis (a relatively small group anyway) then developed symptoms later.

“The proportion of truly asymptomatic infections is unclear but appears to be relatively rare,” the authors of the report wrote.

In the WHO study, 75% of people in China who were first classified as asymptomatic have developed symptoms, ProPublica reported. This technically means that “presymptomatic transmission” is what is probably common.

Other research has confirmed these results. A CDC study of patients with coronavirus in a nursing home in King County, Washington, found that out of 23 people who tested positive, only 10 had symptoms on the day of their diagnosis. Ten people in the other group developed symptoms a week later.

“These results have important implications for infection control,” the authors wrote, adding that many public health approaches “rely on the presence of signs and symptoms to identify and isolate residents or patients who may have COVID.” -19. “

The CDC also evaluated patients with coronavirus on the Diamond Princess cruise ship, which was quarantined in Japan in February. Of the 3,711 people on board, 712 tested positive, but almost 50% of them had no symptoms at the time.

Brooklyn Coronavirus medical PPE mask

A worker wearing personal protective equipment builds a mudguard during a mass production operation to supply New York City with protective supplies March 27, 2020, at the Brooklyn Navy Yard.

AP Photo / John Minchillo

Other examples of asymptomatic and presymptomatic transmission abound

Redfield told NPR that “it looks like we are eliminating an important virus” about 48 hours before the onset of symptoms.

“This explains how quickly this virus continues to spread across the country because we have asymptomatic transmitters and we have individuals who transmit 48 hours before they become symptomatic,” he added. .

A handful of recent studies and reports suggest that presymptomatic and asymptomatic transmission is not unusual.

  • A small study among Japanese expatriates evacuated from Wuhan in February found that 31% of those tested positive had no symptoms.
  • Research that has examined cases of coronavirus in Singapore has revealed that out of 157 locally acquired cases, 10 involved presymptomatic transmission. Scientists have concluded that most exposures by presymptomatic transmission occurred one to three days before a person develops symptoms.
  • Research conducted in China in February found that 13% of the 468 confirmed cases studied involved presymptomatic transmission.
  • The LA Times recently reported that three-quarters of a group of singers who attended a choir practice of 60 people contracted the COVID-19 virus, although none showed symptoms during the practice.
  • Last month, 14 NBA players, coaches and staff tested positive for the coronavirus. Half of them had no symptoms when diagnosed, according to the Wall Street Journal.
  • A biotech company in Iceland that has tested more than 9,000 people has found that about 50% of those who test positive have been asymptomatic, the researchers told CNN.

Presymptomatic people eliminate the greatest amount of virus

A particularly troubling aspect of presymptomatic transmission is that people appear to eliminate more coronaviruses in the early stages of their infection. But the average onset of symptoms takes five days.

Research that has examined 23 coronavirus patients in two hospitals in Hong Kong has revealed that individuals’ viral loads – how many viral particles they carry and release into their environment – peaked in the first week of onset symptoms, then gradually decreased. A SARS patient, on the other hand, clears the virus the most seven to 10 days after being visibly ill.

China comes back to life after coronavirus trip

People wearing face masks lead an escalator to the exit of a metro station following an epidemic of coronavirus disease (COVID-19) in Beijing, China, March 30, 2020.

Carlos Garcia Rawlins / Reuters

A Guangzhou study found similar results: among 94 patients, people were most contagious when symptoms started to appear, or just before.

Children may be asymptomatic carriers

A potential group of asymptomatic carriers could be children. So far, children are among the least sick with coronavirus – but some may get very mild infections and then spread the virus.

Research published Wednesday in The Lancet examined 36 children who tested positive for the coronavirus between January 17 and March 1 in three Chinese hospitals. Half of these children had “a mild illness with no symptoms,” the authors wrote.

child coronavirus

A child wears a face mask at Ninoy Aquino International Airport in Manila, the Philippines, February 3, 2020.

Ezra Acayan / Getty Images

Another study, which has not yet been peer reviewed, found that 56% of the 700 children infected with COVID-19 in China had mild symptoms, if any.

John Williams, a pediatric infectious disease expert at the University of Pittsburgh Medical Center, told ABC that “asymptomatic infection is common in children, occurring in 10 to 30 percent” of cases.

Wearing masks could help reduce presymptomatic transmission

The WHO and CDC have not yet recommended that healthy members of the general public wear masks when going out in public; only healthcare workers are required to use face protection. But the White House is expected to announce a new policy, based on CDC guidelines, that would encourage Americans to wear cloth masks while traveling, the Washington Post reported.

The prevalence of presymptomatic transmission is probably the main reason for the change.

Dr. Anthony Fauci, director of the National Institute of Allergies and Infectious Diseases, told CNN on Wednesday that he “would lean towards” asking everyone to wear masks “if we don’t have the problem of removing the masks of healthcare workers who need them. their. “

Anthony Fauci Stephen Lynch

Representative Stephen Lynch ties up with Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, before Fauci testified before a House oversight committee.

Photo AP / Patrick Semansky)

He added that the change could be significant “especially now that we get the impression that there is transmission of infection from an asymptomatic person who does not cough, who does not sneeze, who looks just fine. “

Most face protection does not benefit the wearer; instead, the masks mainly protect others from the wearer’s germs, as they might be infected but not know it.

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