COVID-19: Many people could still be infectious after 5-day quarantine

After a five-day quarantine, about a third of people infected with SARS-CoV-2, the coronavirus that causes COVID-19, might still be infectious, according to new data.

PCR tests detect virus particles but cannot tell whether they are infectious or merely inactive remnants.

For a study using samples obtained from March through November 2020, researchers used a new test.

In sequential samples from 176 people with positive PCR tests, they looked for genetic material that the virus produces when it is actively making copies of itself and is still transmissible. “At five days, 30 percent of people still exhibited clinically relevant levels of potentially active virus,” said study leader Lorna Harries of the University of Exeter Medical School in England.

After a 10-day quarantine, one in 10 people might still be infectious, her team reported on Thursday in the International Journal of Infectious Diseases.

Some people retained these levels for up to 68 days, the researchers said. “There was nothing clinically remarkable about these people, which means we wouldn’t be able to predict who they are,” Harries said in a news release.

The study was conducted before the Delta and Omicron coronavirus variants began circulating last year.

The researchers intend to conduct larger trials to confirm their findings. In the meantime, they suggest, in facilities “where onward transmission would be especially problematic, it may be prudent to obtain molecular evidence of remission to prevent ongoing transmission.”