A group of Covid-19 patients who were discharged from a community care facility yesterday despite testing positive are not infectious and do not pose a threat to the community, said the Ministry of Health (MOH).
This is because the 18 patients are shedding "dead viral components", which, though detectable in testing, are inactive and no longer transmissible and infectious to others, it added.
The patients, who stayed at the D'Resort community care facility - meant for those with mild symptoms and lower risk factors - were clinically well but "persistently" tested positive for Covid-19, said MOH.
They had stayed at the NTUC resort in Pasir Ris for between 38 and 51 days, it added. "After careful consideration, MOH decided that these individuals can be cleared for discharge," said a spokesman.
These are the first reported cases of patients here being discharged without first testing negative for the virus twice on consecutive days - a standard procedure before patients can be discharged.
The patients will need to quarantine themselves at home for another seven days as an added precaution, MOH said, adding that a medical review committee had carefully considered each case individually prior to their discharge.
In a CNA report yesterday, one of the patients expressed relief at being discharged, but was concerned about still testing positive. She was advised to go home, stay indoors and not be in the same room as her parents.
Infectious diseases experts have told MOH that patients, even if they continue to test positive in the polymerase chain reaction (PCR) test, are unlikely to be infectious beyond 14 days from the onset of illness as the virus can no longer be cultured from biological samples taken from them.
MOH said it will continue to adopt a "cautious approach" and consult local and international medical experts. "We will review the status of Covid-19 patients with prolonged stays at our community care facilities and consider if they need to remain in isolation, on a case-to-case basis," it said.
Highly sensitive PCR tests, which detect genetic sequences specific to Covid-19, are first used to determine the presence of the virus, with a more sophisticated culture method used in laboratories then applied to determine if the virus is alive or dead.
National Centre for Infectious Diseases executive director Leo Yee Sin told The Sunday Times yesterday that the virus is most infectious in the early stages of a patient's illness.
However, by day seven or eight, the virus levels in the patient would have fallen significantly, she said. By day 10 to 14, samples of the virus collected from the patient would no longer be able to be cultured, or artificially grown in a lab, due to very low levels. This means that when the active virus is no longer detected in the patient past day 14, he or she is deemed not infectious.
Dr Leong Hoe Nam, an infectious diseases expert at Mount Elizabeth Novena Hospital, said that past the 21-day mark, "clear, detectable neutralising antibodies are in the blood and destroying all live virus in the body".
"Let's not stigmatise the patients. They didn't choose to have the virus," he said.
Inactive virus can stay in patients for months
The inactive virus can remain in the respiratory tract for a long time, sometimes for months, said Professor Leo Yee Sin, executive director of the National Centre for Infectious Diseases.
That is why some patients falsely test "positive" for the virus, even though they are not infectious.
The respiratory tract will shed its cells over time, like skin does, and some of these cells on the surface - called epithelial cells - may contain inactive virus fragments.
"It's just like sweeping the floor - you have to sweep for quite some time before you clear all the debris. It's the same thing," Prof Leo said.
Similar cases in China, Japan and South Korea, where recovered patients had retested positive for the coronavirus, turned out to be false positives due to faulty testing procedures.