A study of dozens of COVID-19 patients in China found that 42 percent showed no symptoms of the disease but were contagious for shorter periods of time than symptomatic patients.
The study of 78 patients published in the Journal of the American Medical Association (JAMA) found COVID-19 patients who did not show symptoms of the disease were more likely to be younger and female; it also showed that symptomatic patients shed the virus for a median of 19 days, while patients with no symptoms shed the virus for a median of eight days.
“Although patients who were asymptomatic experienced less harm to themselves, they may have been unaware of their disease and therefore not isolated themselves or sought treatment, or they may have been overlooked by health care workers and thus unknowingly transmitted the virus to others,” wrote researchers at Wuhan University in China, where the outbreak was first discovered.
The authors wrote that identifying and isolating asymptomatic coronavirus patients as early as possible is "critical to control the transmission of COVID-19."
“Close contacts of patients with COVID-19 should be closely monitored to avoid secondary transmission,” the authors wrote.
In China, close contacts of confirmed COVID-19 cases are screened for the infection since many people may not show symptoms but can still be contagious.
In the U.S., the spread of the virus by people not experiencing symptoms has challenged the COVID-19 response.
It is still not clear how many people have the virus but aren’t showing symptoms, which is why the Centers for Disease Control and Prevention (CDC) recommends face coverings be worn in public when it is not possible to stay at least six feet away from others.