New research suggests COVID-19 patients remain capable of transmitting the virus for several days after all symptoms of infection have disappeared.
One small study, published in the American Journal of Respiratory and Critical Care Medicine in the paper, Time Kinetics of Viral Clearance and Resolution of Symptoms in Novel Coronavirus Infection (DOI: 10.1164/rccm.202003-0524LE), showed that COVID-19 patients were still shedding the virus for up to 8 days after symptoms were no longer experienced.
“The most significant finding from our study is that half of the patients kept shedding the virus even after resolution of their symptoms,” said co-lead author of the study Lokesh Sharma, PhD, instructor of medicine at Yale School of Medicine. “More severe infections may have even longer shedding times.” The researchers have recommended patients continue to self-isolate for at least two weeks after the symptoms have disappeared.
The study was conducted on 16 patients who had received treatment at the Treatment Center of PLA General Hospital in Beijing between January 28 and February 9, 2020. The patients had experienced a range of mild symptoms which included fever, continuous cough, throat pain, and respiratory difficulty. Only one of the patients required respiratory support. Throat swabs were taken on alternate days after symptoms had disappeared and polymerase chain reaction (PCR) tests were performed.
For all but one of the patients, the incubation period was determined to be 5 days and symptoms lasted for an average of 8 days. The subsequent tests confirmed that more than half of the patients remained viral positive after symptoms had disappeared, with the virus detected for between 1 and 8 days. The researchers suggest that in more severe infections, viral shedding may take even longer.
That view has been backed up by a larger study published in The Lancet. In the paper, Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study (DOI: 10.1016/S0140-6736(20)30566-3), the median time of viral shedding was 20 days in survivors, with the longest time to clear the virus being 37 days. This was a much larger study, conducted on 191 patients, 91 of whom died in hospital.