Can patients continue to shed the virus that causes COVID-19 after symptoms have disappeared? Yes -- and at least half do, according to a study published online March 23 in the American Thoracic Society's (ATS) American Journal of Respiratory and Critical Care Medicine.
Researchers found that patients treated for mild COVID-19 still had the virus for up to eight days after symptoms resolved -- a result that underscores the difficulty of curbing the disease.
"Our study provides initial insights into the viral clearance kinetics and the ability of the virus to persist even after the resolution of [symptoms] for as long as eight days, which may pose a significant challenge in controlling the spread of the disease," wrote lead co-author Lokesh Sharma, PhD, instructor of medicine in the section of pulmonary, critical care, and sleep medicine at Yale University, and colleagues.
The COVID-19 pandemic is the "third and the most lethal outbreak of coronavirus in the 21st century," the group noted, and its ability to spread appears to arise from transmission from asymptomatic patients.
"Cases have been reported where a patient could infect their close contacts even after 'apparent recovery' from the infection," the authors wrote. "This warrants [investigation into] the 'shedding window' after the clinical recovery of the patient."
Sharma and colleagues sought to investigate the time frame of "viral clearance" as it related to the resolution of COVID-19 symptoms. Their study included 16 patients (median age, 35 years) who were treated for the disease and released from the hospital between January 28 and February 9. The time from infection to the onset of symptoms was five days for all patients except one, and the average duration of symptoms was eight days. Patients were discharged after negative viral status was confirmed by at least two consecutive polymerase chain reaction (PCR) tests; they were asked to quarantine for 14 days at home and to present at the hospital for a follow-up visit one week after discharge to confirm negative virus status.
Eight patients were discharged after negative test results. But eight others tested positive for the virus, even after their symptoms disappeared, over a timeline that ranged from one to eight days.
"The most significant finding from our study is that half of the patients kept shedding the virus even after resolution of their symptoms," Sharma said in a statement released by the ATS. "More severe infections may have even longer shedding times."
The study is congruent with two others, one published March 16 in Science and the other to be published in the May issue of Emerging Infectious Diseases, in which researchers found that the novel coronavirus can spread before patients are symptomatic: A team from the University of Texas at Austin found that more than 10% of patients are infected by asymptomatic virus carriers, while researchers from Columbia University Mailman School of Public Health found that a high percentage of undetected cases contributed to the spread of the virus in China.
Sharma and colleagues acknowledged that the study cohort was small, and that it's unclear whether similar results would be found in older people, those with weak immune systems, and those on immunosuppressive therapies.
However, the findings do offer useful guidance to both patients and physicians, according to the group. Patients with mild COVID-19 symptoms should be advised to extend their home quarantine for another two weeks after symptoms abate, and physicians should take the possibility of patients continuing to be contagious under consideration.
"COVID-19 patients can be infectious even after their symptomatic recovery, so treat the asymptomatic/recently recovered patients as carefully as symptomatic patients," co-author Dr. Lixin Xie, a professor of pulmonary and critical care medicine at Chinese PLA General Hospital in Beijing, said in the ATS statement.
"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," he added.