Researchers at the Treatment Center of PLA General Hospital in Beijing, China, have found that half of the patients they treated for mild COVID-19 disease still had coronavirus for up to 8 days after symptoms disappeared.
“The most significant finding from our study is that half of the patients kept shedding the virus even after resolution of their symptoms,” said Yale University’s Dr. Lokesh Sharma, co-lead author of the study.
“More severe infections may have even longer shedding times.”
The study included 16 patients (median age of 35.5 years) with COVID-19 who were treated and released from the Treatment Center of PLA General Hospital between January 28 and February 9, 2020.
The scientists collected samples from throat swabs taken from all patients on alternate days and analyzed.
Patients were discharged after their recovery and confirmation of negative viral status by at least two consecutive PCR tests.
The primary symptoms in these patients included fever, cough, pain in the pharynx (pharyngalgia) and difficult or labored breathing (dyspnea). Patients were treated with a range of medications.
The time from infection to onset of symptoms (incubation period) was 5 days among all but one patient.
The average duration of symptoms was 8 days, while the length of time patients remained contagious after the end of their symptoms ranged from one to 8 days.
Two patients had diabetes and one had tuberculosis, neither of which affected the timing of the course of COVID-19 infection.
“If you had mild respiratory symptoms from COVID-19 and were staying at home so as not to infect people, extend your quarantine for another two weeks after recovery to ensure that you don’t infect other people,” said PLA General Hospital’s Professor Lixin Xie, co-author of the study.
The researchers had a special message for the medical community:
“COVID-19 patients can be infectious even after their symptomatic recovery, so treat the asymptomatic/recently recovered patients as carefully as symptomatic patients.”
They emphasized that all of these patients had milder infections and recovered from the disease, and that the study looked at a small number of patients.
They noted that it is unclear whether similar results would hold true for more vulnerable patients such as the elderly, those with suppressed immune systems and patients on immunosuppressive therapies.
“Further studies are needed to investigate if the real-time PCR-detected virus is capable of transmission in the later stages of COVID-19 infection,” Professor Xie said.
The study was published in the American Journal of Respiratory and Critical Care Medicine.
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De Chang et al. Time Kinetics of Viral Clearance and Resolution of Symptoms in Novel Coronavirus Infection. American Journal of Respiratory and Critical Care Medicine, published online March 23, 2020; doi: 10.1164/rccm.202003-0524LE