What To Know About Asymptomatic COVID-19 Cases

To me, one of most troubling aspects of COVID-19 is that you could have the virus and not know it. Although more research needs to be done, some scientists believe as many as 20% of cases might be asymptomatic. This means a person is infected without showing any symptoms, such as a cough, shortness of breath, or a loss of taste and smell.

The reason the potential to be asymptomatic is so worrisome to me — and to many experts — is that if you don't feel sick, you won't know to quarantine yourself. You could be going about your usual routine, risking passing on the virus wherever you go.

More research needs to be done to determine why one person infected with COVID-19 might not feel so much as a tickle in their throat, while others become severely ill. But we asked doctors to tell us what we do know — if there are any red flags that indicate you might be an asymptomatic carrier, and what you should do if you suspect you are. Here's what we know so far.

If you're asymptomatic, you would be positive for COVID-19 if you took a test, but you don't feel any of the symptoms of the virus, such as fever or a loss of taste and smell.

This is different than having "presymptomatic COVID-19." That's when you get a positive test before you notice any symptoms — but you do develop them later, according to the Centers for Disease Control and Prevention. 

Many people think they're asymptomatic when they're not, because they have mild symptoms of COVID-19 or symptoms they don't associate with the illness. “This virus has shown to be very atypical in terms of how it presents,” explains Darien Sutton, MD, an emergency medicine physician. “Early on, we thought it was primarily causing respiratory symptoms, but as time went on we started to see that people started to have headache, body aches, and diarrhoea, and even additional complaints such as non-specific skin changes, much of which might not present because people might not even think of it.”

Early in the pandemic, there were reports that asymptomatic cases of COVID-19 were more common than we believe them to be now. In May, for instance, 81% of 104 COVID-19-positive people on board a quarantined cruise ship were found to be asymptomatic, according to an article in the BMJ Journals Thorax. As we test more people and gain a better understanding of the disease, however, studies are indicating that the prevalence of asymptomatic cases is much lower. For instance, only 20% of patients said they developed no symptoms at all over the course of their illness in a September analysis of 79 international studies, reports PLOS Medicine.

Age and overall health may also play a role in how likely someone is to develop symptoms. In an investigation of a nursing home in King County, Washington, for example, only 4% of those who tested positive for COVID-19 actually remained asymptomatic throughout the course of their illness.

Ultimately, more research and testing will need to be done before we can say for certainty how common this is.

Mostly likely, yes. In the PLOS analysis, asymptomatic people seemed less likely to infect others than symptomatic and presymptomatic folks. But that doesn't mean asymptomatic people don't transmit the virus. What's more, as we said earlier, asymptomatic people who don't realise they're positive may risk passing on COVID-19 by going about their daily routine. So be careful, and keep doing the things that we know work to prevent the spread, including wearing a mask (and maybe using mouthwash) and trying to stay away from people outside of your pod all the time, whether you feel sick or not.

"The contribution of presymptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand and respiratory hygiene, testing and tracing, and isolation strategies and social distancing, will continue to be needed,” the PLOS Medicine study authors said in a news release.

Additionally, there's some evidence that people with asymptomatic COVID-19 may be less likely to produce lasting antibodies — the proteins that help your body fight off the virus often associated with future immunity to it — than people with more severe cases, according to a study published in June in Nature Medicine. That means an asymptomatic person may be at risk for catching the virus again in two or three months.

You can't, unless you happen to get a test for some reason despite having no symptoms and it comes up positive — or you get an antibody test and realise later than you had it. In the most cut-and-dry asymptomatic cases, there’ll be no symptoms to look out for at all. That's why it's important to be so diligent about the precautionary measures — and for people who do test positive to tell everyone they were in contact with the days and weeks before that they may have been exposed.

"There’s no way to know who’s going to be asymptomatic," adds Anurag Malani, MD, the medical director of infection prevention and antimicrobial stewardship programs at St. Joseph Mercy Health System. "It's probably a younger demographic with fewer comorbidities, but the thing is we don't always know for sure."

If you think or know you've been exposed to someone who has tested positive for COVID-19, it's a smart idea to quarantine yourself for 14 days and consider getting tested. Whether you're asymptomatic, presymptomatic, or mildly symptomatic, the best thing you can do is try your best to avoid passing on the virus to anyone else — which means staying indoors alone or with your "pod", and being extra-diligent about wearing a mask, sanitising your hands, and socially distancing if you have to go out.

“Asymptomatic responses to COVID-19 are a possibility, but we have also seen cases where people become dangerously ill and need hospitalisation,” Dr Sutton says. And you won't know what your outcome will be until you’re infected. That’s why he says it’s wise to be cautious. 

“If you happen to be an asymptomatic carrier, you may spread that to someone you know — a grandparent, a friend, a coworker,” Dr Sutton adds. “I would ask people, 'how much risk do you want to take?' Why take the chance? Wear a mask and keep your distance as much as possible.”