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Covid-19 symptoms vary widely, and undertesting in many countries means that many people may have already had the coronavirus without having received a positive diagnosis. Is it possible to find out, and how should you behave if you think you may have been infected?
Is there any way to know whether someone has had Covid-19 in the past?
Dr William Hillmann: At this point, we don’t have a test to tell that. We are developing antibody tests to check for a prior infection, but those aren’t ready for clinical use yet. The only definitive way to know that you’ve had it is to get tested while you have it and to have that test be positive.
Could I have had it and been asymptomatic?
Hillmann: Coronavirus is actually quite a significant spectrum of symptoms, from people who are entirely asymptomatic and would have no idea that they have it to people with very mild, cold-like symptoms – runny nose, congestion, sore throat – to people with more flu-like symptoms – high fevers, muscle aches, shortness of breath and cough. All the way up to people with severe illness, who we’re seeing in the hospital with respiratory failure, requiring ICU care. (Editor’s note: recent reports suggest that loss of smell and taste are also signs of Covid-19 infection.)
What percentage of carriers are asymptomatic?
Dr David Buchholz: Right now in New York, we’re only testing the sickest possible people. So we have no idea. However, there was a study in Iceland, which tested [a large segment of its] population, and 50% of the people who tested positive had no symptoms.
Are people who are asymptomatic also contagious?
Hillmann: A significant proportion of people who are totally asymptomatic are contagious for some portion of time. We just don’t know [for how long] at this point, because we don’t have the kind of testing available to screen for asymptomatic infections.
When people are symptomatic, they’re contagious. A day or two before they become symptomatic, they’re likely contagious as well. A virus builds up and starts to shed, and then after symptoms resolve, people can still be contagious for a couple of days. We have some evidence of viral shed even a couple of weeks after symptoms are resolved. It’s hard to know if that’s actual live virus, which is still able to infect somebody, or if that’s just dead virus that the body is shedding.
Should someone behave differently if they think, but don’t know for certain, that they have already had it?
Buchholz: We all have to be role models. If we’re all in it together, we all should be doing social distancing.
Hillmann: Since there’s no real way to know at this point who might have had it, unless you’re symptomatic, you get a swab and are definitively diagnosed with it, I would just act as if you hadn’t had it. Keep doing all of those things that we all should be doing at this point: social distancing and hand hygiene.
If I think I may have had it, do I have an ethical obligation to tell people I came in contact with? Even if it may in fact just have been a cold?
Buchholz: I would, absolutely. I’m in New York, and it was definitely in the community before we knew it. So, yeah, any family members and close friends, maybe somebody you work next to, I think I would just alert them, especially if it was in the last 14 days. If it’s been more than 14 days, they would have gotten sick by now if they had significant exposure.
Hillmann: It’s up to every individual about what they feel is right. If somebody is diagnosed with a case of coronavirus, I might feel a little bit more strongly that they should tell people because if you’re in close contact with a healthcare worker, it could have implications for precautions that healthcare worker needs to take.
If I’ve had it, can I get it again?
Buchholz: There’s not been any evidence that anyone’s gotten it more than once. Someone with a normal immune system that can react to the virus and get better should have immunity for quite some time, at least a year, if not lifelong.
There have been reports out of China suggesting people are testing positive for Covid-19 a second time. Most scientists think it is an issue around the inaccuracy of the testing and not that people are having two separate cases of the disease.
Dr David Buchholz, senior founding medical director, primary care, assistant professor of pediatrics, Columbia University Irving medical center
Dr William Hillmann, associate inpatient physician director at Massachusetts general hospital
Due to the unprecedented and ongoing nature of the coronavirus outbreak, this article is being regularly updated to ensure that it reflects the current situation as best as possible. Any significant corrections made to this or previous versions of the article will continue to be footnoted in line with Guardian editorial policy.