How long until a clean bill of health?

Medical experts grapple with what follows COVID-19 patient recovery

In the coming weeks, thousands of people in Ottawa are expected to recover from mild cases of COVID-19 — many more than are hospitalized with the respiratory disease.

The city’s medical officer of health, Dr. Vera Etches, has said that as many as 4,000 people could now have COVID-19 in Ottawa, and studies from China suggest that more than 80 per cent of those infected will recover without medical intervention. But once they’re back on their feet, how long will these people remain infectious and a danger to others in the same household? Should they be tested to ensure they’re no longer passing on the virus? And if not, how long should they remain in isolation? What’s more, will recovered patients have immunity against a second COVID-19 infection?

The answers to those questions will ultimately spell out how this pandemic ends. Those answers also hold profound implications for the health care system, which will have to establish how and when recovering COVID-19 patients can be discharged from hospital, along with when infected doctors and nurses can return to the front lines.

In a teleconference Wednesday, Dr. Etches said consensus recommendations on those questions are still emerging.

“The science is evolving,” she told reporters.

Right now, she said, Ottawa Public Health is recommending that someone with a suspected case of COVID -19 should remain in isolation for at least 10 days after their symptoms appear. “Going 10 days after the symptoms started is protective,” she said.

Even after 10 days, Etches added, if a fever or cough persists, that individual should remain in isolation until those symptoms resolve: “So it’s whichever is longer: 10 days or 24 hours after the end of the symptoms, then people can consider themselves no longer infectious.”

The recommendations, she said, are based on studies that have shown that after eight days, virus samples from most COVID-19 patients are “no longer viable to cause infection.”

A new German study, not yet peer reviewed, offers some of the best available evidence. That study suggests that COVID-19 patients are most infectious early in the course of their disease, and that those with mild cases are at low risk of spreading the virus 10 days after they first experienced symptoms.

The German researchers studied the viral shedding of nine patients, all with relatively mild cases of COVID-19, by taking nose and throat swabs for 22 consecutive days. They also tested sputum and stool for the virus’s genetic material.

Researchers found that patients were most infectious — their sputum contained the highest levels of active virus — on Day 4 of their illnesses. However, in the two most serious cases, involving patients who showed some signs of pneumonia, the viral loads did not peak until much later, around Day 10.

Among patients with milder cases, there was evidence that they were much less infectious after a week of illness: Scientists were unable to grow viruses in the lab from sputum or swabs taken eight days after the onset of COVID-19.

“Based on the present findings,” the researchers concluded, “early discharge with ensuing home isolation could be chosen for patients who are beyond Day 10 of symptoms with less than 100,000 viral RNA copies per millilitre of sputum. Both criteria predict that there is little residual risk of infectivity, based on cell culture.”

Studies have shown that traces of the coronavirus can persist in the body for up to two weeks after symptoms have resolved. The chances of passing on the virus, however, are much reduced.

According to guidelines published by the U.S. Centers for Disease Control and Prevention (CDC), people with COVID -19 who have stayed home can emerge from isolation provided they have not had a fever for three days (without using medicine to control a temperature); their other symptoms have improved; and at least seven days have passed since the illness first appeared.

Testing can also establish infectivity: Two negative swab tests, two days apart, can confirm that a COVID-19 patient is no longer a danger to other people.

Dr. Jerome Leis, medical director of infection prevention and control at Toronto’s Sunnybrook Health Sciences Centre, said the province does not have enough testing capacity to assess whether every COVID-19 patient is no longer infectious.

It means, Leis said, that anyone with cold or flu-like symptoms must assume that they have COVID -19 and isolate themselves for the recommended time period. “I think we need to be conservative,” he said.

Once recovered from COVID -19, people should have immunity to a second infection — at least for a while. But again, the science is not yet definitive.

Experience with other respiratory coronaviruses suggests that the protective effect of antibodies is not permanent, but lasts for a year or two after infection. One study found that MERS patients still had antibodies two years after being infected with the coronavirus. “But it is not yet known whether similar immune protection will be observed for patients with COVID-19,” the CDC warns.

Dr. Etches said Wednesday that the best information suggests “it’s likely people will have immunity for a number of months.”

“We don’t have any proof of that yet,” she said.

“There are studies underway to identify the antibodies for COVID-19. That will be useful: Then we’ll be able to tell if someone has been infected and if they have immunity. But we’re just not there yet.”

Scientists around the world are now racing to develop a blood test for COVID-19 antibodies.