The study, published in the American Journal of Respiratory and Critical Care Medicine, looked at Chinese patients who contracted coronavirus in late January or early February.
Eight of 16 patients who had been admitted to PLA General Hospital in Beijing still carried the virus well after they believed themselves to be healthy, the Yale University School of Medicine researchers found.
Some were still infectious as many as eight days after their coughs and fevers had gone away.
The study calls into question whether a 14-day quarantine period for coronavirus patients – a protocol adopted by countries all over the world, including New Zealand – is long enough.
“The most significant finding from our study is that half of the patients kept shedding the virus even after resolution of their symptoms,” said Dr Lokesh Sharma, the study’s co-lead author.
“More severe infections may have even longer shedding times.”
Coronavirus is known to spread most frequently by droplet transmission, which occurs when an infected person is in close contact with another person. This is why self-isolation is such a common tool around the world in the fight against COVID-19.
The novel coronavirus is a global pandemic. There are already 784,000 positive cases of the disease around the world, which has caused the deaths of more than 37,000 people.
New Zealand has 647 positive cases. One person has died of the virus here so far.