Most COVID-19 patients are no longer infectious 11 days after developing symptoms of the deadly disease, according to a new study by infectious disease experts in Singapore, findings that may affect patient discharge policies.
After examining the “viral load” in 73 COVID-19 patients, experts from Singapore’s National Center for Infectious Diseases (NCID) and the Academy of Medicine found that the virus “could not be isolated or cultured after day 11 of illness,” they said in a joint statement (pdf).
Patients who continue to test positive for the Chinese Communist Party (CCP) virus, the novel coronavirus that causes COVID-19, on day 12 and beyond, are likely doing so because of virus fragments that are no longer infectious, the study found.
“Active viral replication drops quickly after the first week, and viable virus was not found after the second week of illness,” the researchers wrote.
Patients with weakened immune systems are exceptions, and in such cases, the virus could be viable longer, they noted.
“Based on the accumulated data since the start of the COVID-19 pandemic, the infectious period of SARS-CoV-2 in symptomatic individuals may begin around two days before the onset of symptoms, and persists for about 7-10 days after the onset of symptoms,” the researchers stated.
NCID Executive Director Leo Yee-Sin told the Singapore newspaper The Straits Times that while the patient sample size in the study was small, she believes the conclusions of the study are sound.
“Scientifically, I’m very confident that there is enough evidence that the person is no longer infectious after 11 days,” she said.
COVID-19 patients in Singapore are currently discharged based on two negative tests, similar to de-isolation guidelines in the United States released by the Centers for Disease Control and Prevention (CDC), which call for two negative tests in a row, at least 24 hours apart.
Singapore’s Ministry of Health told The Straits Times it would examine the study carefully to see if it merits a change in policy related to discharging COVID-19 patients.
The Singapore study follows a similar one in South Korea, which found that patients who recovered from COVID-19 but later tested positive didn’t pass the virus to others while they were “re-positive.”
Scientists from the Korean Centers for Disease Control and Prevention identified 790 people, including 351 family members, who came into contact with nearly 300 of around 450 patients who recovered from the virus, but later tested positive.
Researchers didn’t find a single case of anyone becoming infected after coming into contact with the recovered patients who again tested positive.
“As of now, no case has been found that was newly confirmed from exposure during re-positive period alone,” researchers wrote in a May 19 report (pdf).
Researchers in South Korea put forward a theory similar to the Singaporean experts, which is that non-viable virus fragments remain in patients after recovery.
“We’re putting more weight on the theory that dead virus fragments remain in a recovered patient’s body, since we haven’t seen evidence of infectivity,” Ki Moran, a professor at the National Cancer Center who’s advising the South Korean government, told The Wall Street Journal.
More research is required to determine why patients are re-testing positive for the virus, officials cited in the report said.