Research has indicated that, of those who show symptoms of COVID-19, most will likely do so within five days of being infected by SARS-CoV-2, the virus that causes the disease. However, how long people remain contagious once they are infected is proving to be a difficult question for researchers to answer.
According to Reuters, on Apr. 10, South Korean officials reported 91 patients who had recovered from COVID-19 had once again tested positive for the novel coronavirus. The World Health Organization is looking into the claims, which the director of the Korea Centers for Disease Control and Prevention says are likely cases of the virus being “reactivated” rather than patients being infected with the virus again, Reuters says. It’s not certain whether such patients would still be contagious.
Information on the CDC website as of Apr. 13 says those diagnosed with COVID-19 who haven’t been tested for the virus can stop self-isolation once their fever has gone away for three days without taking medication, other symptoms such as coughing and difficulty breathing have improved, and at least seven days have passed since they first started showing symptoms. For those who will be re-tested, they can stop self-isolating once they no longer have a fever without taking medication, other symptoms have improved, and they have received two negative tests in a row, 24 hours apart.
Research so far shows that the time period from COVID-19 symptom onset to the first negative test for the virus is around nine days, on average. Another study confirmed those results, showing that among the 16 patients they looked at, most showed symptoms for eight days. However, that study also showed that half of those patients still tested positive for the virus even after their symptoms vanished. Based on those results, the researchers recommend that those diagnosed with COVID-19 should continue to self-isolate for another two weeks after their symptoms disappear as an added precaution. Other research has shown that, in some patients, the virus is still present in saliva and feces samples even after it has been cleared from pharyngeal samples. However, it’s not clear how contagious those individuals would be at that point.
A study by researchers in Germany indicated that virus shedding was highest during the first week of infection and people were far less infectious by day 10 of symptoms. Hospitalized people who were beyond day 10 of symptom onset could likely be safely discharged to self-isolate at home, provided they had “less than 100,000 viral RNA copies per ml of sputum,” the researchers said, adding that “both criteria predict that there is little residual risk of infectivity, based on cell culture.”
Researchers also note that the positive tests of patients thought to be clear of the virus could be an issue with the real-time PCR tests used to detect the virus and that, as most of these studies are based on early cases of the disease and relatively small numbers of patients, more research is needed before we know definitively how long people with COVID-19 remain contagious.
Editor’s note: This article is intended to be a summary of the current research on contagiousness of COVID-19 rather than provide advice on how long you should self-isolate once you are diagnosed. As COVID-19 is a quickly evolving situation, always follow the recommendations of your local health authority, such as the CDC or your health care provider for the most current knowledge.