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Is it possible to be infected with the coronavirus and show no symptoms? Or go through a period of several days before symptoms appear?
And even at this stage with no cough, no fever, no signs of illness, could you pass the virus on to others?
“There is evidence that SARS-CoV-2 has this ability to spread silently,” says Shweta Bansal, an infectious disease modeler at Georgetown University.
In fact, COVID-19 cases among nursing home residents, choir groups, and families fuel growing concern for infected people, but generally feel good and get on with their daily lives, passing the virus on to friends, family and strangers without knowing that they have it themselves.
But there are big gaps in our understanding of how many people fit this category of “silent spreaders,” as some public health researchers call them, and how much they contribute to disease transmission.
Silent spreaders can be divided into three categories: asymptomatic, presymptomatic, and very mildly symptomatic. This is what we know about these variations.
Asymptomatic: People who carry the active virus in their body but never develop any symptoms.
“Nothing at all,” says Tara C. Smith, an epidemiologist at the Kent State University College of Public Health. “No fever, no gastrointestinal problems, no respiratory problems, no cough, none of that.”
As you can imagine, it is difficult to notice when someone has a disease but shows no signs of it.
Some cases of asymptomatic carriers have been confirmed by finding and evaluating people who were in close contact with patients with COVID-19. For those who tested positive without symptoms, follow-up exams confirmed that about 25% continued to show no signs, World Health Organization officials said April 1, citing data from China.
No one can really determine the impact of asymptomatic cases on spread until there is more evidence. But so far, they have made up a small portion of the total number of people who tested positive. And affected individuals appear to bias young. A small clinical study from Nanjing, China followed 24 people who tested positive but showed no obvious symptoms at the time. Within one to three weeks after diagnosis, seven continued to show no symptoms. Their median age was 14.
“Can those people who are completely asymptomatic, who never develop symptoms, transmit the infection? That remains an open question,” says Smith.
Presymptomatic: People who have been infected and are incubating the virus but still show no symptoms.
After infection, symptoms may not develop for five to six days, or even two weeks, depending on the Annals of internal medicine. The time between the capture of the virus and the appearance of symptoms is called the presymptomatic phase.
How do these individuals figure in the broadcast?
People appear to be more infectious when symptoms begin, said Maria Van Kerkhove, technical manager of the WHO Health Emergencies Program, at a press conference on April 1. However, “we have evidence, testing, and model studies, that suggest presymptomatic people can definitely transmit this virus,” says the epidemiologist, Smith, most likely within one to three days before symptoms begin to show. , according to the WHO.
Until now, presymptomatic is a much more common category than asymptomatic. About 75% of people who test positive without showing symptoms turn out to be presymptomatic, showing cough, fatigue, fever and other signs of COVID-19 on a subsequent follow-up exam, Van Kerkhove said.
At a King County, Washington, nursing home, about a third of its 82 residents tested positive for coronavirus in mid-March. Half of those who were free of fever, malaise and cough when the virus was sampled, although most developed symptoms. The coronavirus spread rapidly through the facility just two weeks after a healthcare provider introduced it, despite the nursing home’s policy of isolating residents with signs of COVID-19. This suggests that “transmission of asymptomatic and presymptomatic residents, who were not recognized as having SARS-CoV-2 infection and therefore not isolated, may have contributed to further spread,” according to research published in the journal. CDC’s Morbidity and Mortality Weekly on April 3. Report.”
A study in Singapore found similar evidence of presymptomatic spread among people who attended church, took singing lessons, or slept at home with their spouses.
Very mildly symptomatic: People who feel a little bad about an infection with COVID-19 but continue to be in close contact with other people.
“We are very fortunate that this is not a serious infection for everyone, but because of that, some people feel a little sick and powerful,” says Seema Lakdawala, a flu researcher at the University of Pittsburgh.
The spread of COVID-19 while having a very mild cough or fever does not fully count as silent transmission, says Bansal, the infectious disease modeler: “There is at least some sign there.”
But people who continue to frequent public and communal places with a mild cough or mild fever may inadvertently transmit the disease in the first few days of the onset of symptoms, when they are believed to be most infectious.
Even when a person’s symptoms remain mild, others who infect can become seriously ill. In mid-January, a man returned home to Nanjing from a trip to Hubei province, the epicenter of the Chinese epidemic. Ten days later, his wife began to have a fever and vomiting; Soon, she developed severe pneumonia and required care in the intensive care unit. The man was examined for the coronavirus, and the test was positive; he is presumed to have spread the virus to his wife. X-ray scans showed signs of the virus in his lungs, but he always reported feeling good, according to epidemiological research published in Chinese Science Life Sciences.
What we don’t know yet
How many people mix in the population without knowing that they have been infected with the coronavirus?
It is simply too early to say. In one of the places where extensive testing has been done, the Washington state nursing home, 56% of those who tested positive had no symptoms when tested. On board the Diamond Princess cruise ship docked in Japan, February data showed that up to 50% of those who tested positive showed no symptoms at the time and that approximately 18% remained asymptomatic.
Are asymptomatic and presymptomatic cases responsible for a lot of transmission?
Uncertainties abound.
Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, told NPR in an interview on April 9 that while he believes “the asymptomatic spread was and is more significant than what was appreciated in January , the relative contribution of asymptomatic spread to symptomatic spread has not been clearly defined. “
A role of modeling in Science suggests that in China before closure, undiscovered cases, mainly people with “mild, limited or no symptoms,” were less infectious than known cases, but were still possibly responsible for 79% of transmission, because many of them They continued to congregate or travel while contagious. Other documents from Singapore and China suggest that presymptomatic cases account for 6% to 13% of transmission.
To begin answering these propagation questions, “we really need more testing and more follow-up,” says Smith.
The National Institutes of Health announced Friday that it is recruiting up to 10,000 volunteers for blood tests to look for antibodies against COVID-19, a sign that a person was infected in the past. “This studio … [tell] how many people in different communities were infected without knowing it, because they had very mild undocumented disease or did not access the tests while they were sick, “said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases., in a statement from press.
Although there is still a lot to learn about silent broadcasting, concerns about this mode of transmission give more weight to the advice we’ve been hearing all along: keep a distance of 6 feet from others, wash your hands frequently, and clean surfaces. “Don’t wait for symptoms to protect those around you,” says Bansal of Georgetown University, because there is increasing evidence that a person with the coronavirus could look and feel as healthy as ever, but still pass it on to others.
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