Scientists have assessed respiratory samples from 35 COVID-19 patients, and found that contagious coronavirus was "rarely detectable" beyond eight days after onset of illness, an advance that can help develop better self-isolation and quarantining protocols to curb the spread of the pandemic.
The study, published in the journal Emerging Infectious Diseases, analysed 68 respiratory specimens from 35 COVID-19 patients in Hong Kong, of whom 32 had mild disease, and found that the novel coronavirus SARS-CoV-2 was rarely detectable beyond eight days after onset of illness.
However, the researchers, including Ranawaka Perera from the University of Hong Kong, said the virus genetic material RNA was detectable for many weeks using the RT-PCR technique. The scientists explained that SARS-CoV-2 RNA detection by RT-PCR does not prove the presence of infectious virus, adding that culture isolation of the pathogen is a better indication of its contagiousness.
They said in patients with predominantly mild COVID-19, virus isolation was positive within the first eight days after onset of illness. Citing previous studies, the researchers said that "virus culture for mildly ill or moderately ill patients showed virus culture was only successful within the first nine days after onset of illness."
"Patients who are severely ill and immunocompromised might shed infectious virus for much longer periods, and this shedding might also be prolonged by corticosteroid therapy," the scientists wrote in the study. According to the research, patients with mild or moderate illness might be less contagious eight days after symptom onset.
"Mildly ill patients who have clinically recovered, and are not immunocompromised, might be discharged from containment in nine or more days after symptom onset, as long as they are not being discharged into settings that contain other highly vulnerable persons," the study noted.