Can the coronavirus (2019-nCOV) be spread by people without symptoms?
It’s been a controversial question ever since a case report in the New England Journal of Medicine (NEJM) last week claimed that a woman who was “asymptomatic” triggered a chain of infections near Munich.
It was a surprising observation because coronaviruses are believed to be spread primarily by people who are already sick, through droplets generated by coughing and sneezing.
The original report said the woman did not show symptoms until later.
“During her stay, she had been well with no sign or symptoms of infection but had become ill on her flight back to China,” the authors wrote.
Because the report was published in one of the most prestigious medical journals in the world, it immediately raised questions about how to manage people exposed to the virus.
But the report was wrong.
The case study was based on faulty information because the original authors did not speak directly to the patient, according to a news report in the journal Science.
The NEJM report was signed by 17 doctors from several German hospitals and research institutes. The Science article quotes one author, Michael Hoelscher of the Ludwig Maximilian University of Munich Medical Centre, who said the information about the asymptomatic visitor came from the infected German patients.
Since then, German health officials have spoken directly with the woman from Shanghai. She told them she was already feeling ill when she met with German colleagues near Munich.
The woman had “mild, unspecific symptoms” while in Germany and took medication to reduce a fever, said Marieke Degen, a spokesperson for Germany’s public health agency, the Robert Koch Institute (RKI), in an email to CBC News.
So far, at least 10 German people including two children have coronavirus (2019-nCOV) infections linked to that business meeting at the Webasto automotive supply company two weeks ago.
The original NEJM report was cited by prominent public health officials as they made decisions about how to handle people potentially exposed to the virus.
On Friday, the U.S. Centers For Disease Control (CDC) held a news conference to outline the quarantine plan for Americans who had been flown home from China.
“While we still don’t have the full picture and we can’t predict how this situation will play out in the U.S., the current situation, the current scenario, is a cause for concern,” said CDC spokesperson Dr. Nancy Messonnier, citing the NEJM report.
Despite that initial report, infectious disease experts continued to insist that most of the risk of infection comes from people who are coughing and sneezing, and already feeling ill.
Asymptomatic vs. ‘subclinical’
Still, the case study raised questions.
“Many of us were open-minded about the possibility of asymptomatic transmission, but also many of us believe that it’s just more likely that symptomatic people would be transmitting the infection,” said Dr. Isaac Bogoch, an infectious disease physician at Toronto’s University Health Network.
The question of asymptomatic spread is still controversial even though this prominent case study was wrong.
There is evidence that people can be infected and show no symptoms. And there are people who have a mild illness and might not seek out medical attention, but will still be able to spread the virus, said Bogoch.
Bogoch prefers the term subclinical. “These are people who have a range of symptoms ranging from zero symptoms to overt symptoms but the symptoms aren’t severe enough such that they seek medical care.”
Subclinical infections are important because there’s a risk that people who are still well enough to go to work and circulate in the community will drive the epidemic, he said.
Scientists and medical journals around the world have committed to sharing information about the coronavirus quickly and openly during this epidemic to help contain and treat the disease. But that rapid turn-around time increases the risk of errors.
“We’re balancing getting as much information out as fast as possible to help with this, but of course, we also have to be careful,” said Bogoch.
“Mistakes happen. Just acknowledge and correct the mistakes.”
So far, the NEJM has not retracted the article.
“We’re working on it but we’re not yet in a position to make a statement or answer additional questions,” the journal told CBC News in an email.
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