Viral Shedding Continues Up to 6 Weeks After Coronavirus Symptom Onset

By Marilynn Larkin

April 28, 2020

NEW YORK (Reuters Health) - Patients may continue to shed the SARS-CoV-2 virus for up to six weeks after symptoms emerge, a small study of recovered COVID-19 patients suggests.

"In the convalescence period, a trace of virus may still be detected," Dr. Sheng Zhang of Huazhong University of Science and Technology in Wuhan told Reuters Health by email. "However, similar to other virus infections, this is not indicative of the transmission ability of the infected individual."

Dr. Zhang and colleagues summarized their experience with 56 COVID-19 patients (median age 55; 61% men) admitted to Tongi Hospital in Wuhan in January and February. Throat or deep nasal cavity swab samples were collected on different dates after symptom onset. SARS-CoV-2 was diagnosed by real-time reverse transcription polymerase chain reaction (RT-PCR) assays All patients had mild-moderate infection.

As reported in Clinical Infectious Diseases, 299 RT-PCR assays were performed (about five tests per patient). The longest duration between symptom onset and an RT-PCR test was 42 days, whereas the median duration was 24 days.

In the first three weeks after symptom onset, the majority of RT-PCR results were positive for SARS-CoV-2. From week three onward, negative results increased. All tests were negative at week six after symptom onset.

The rate of positive results was highest at week one (100%), followed by 89.3%, 66.1%, 32.1%, 5.4% and 0% at weeks two, three, four, five and six, respectively.

Patients were further divided into non-prolonged and prolonged shedding groups based on nucleic acid conversion time (up to or more than 24 days). Patients with longer viral shedding tended to be older and were more likely to have comorbidities such as diabetes and hypertension.

No patients were transferred to an intensive care unit; all recovered and were discharged from the hospital.

Dr. Zhang said, "I would suggest three consecutive negative RT-PCR results to safely discharge, due to high false-negative rate" of nasal or throat swabs.

From a public health perspective, he added, "I need to emphasize that the public should not be scared by those seemingly 'prolonged' positive cases. It is way harder to prove 'no transmission ability' than 'potentially transmissible.'"

Dr. Jack Lipton, Chair of the Department of Translational Neuroscience at Michigan State University College of Human Medicine in Ann Arbor commented in an email to Reuters Health, "The study demonstrates that repeated testing is absolutely necessary. In our clinical trial of university personnel at MSU, we have a young healthy subject with mild symptoms who has tested positive five times over four weeks. People need to realize that a 14-day isolation is appropriate for seeing whether one will develop symptoms after a known exposure to an infected person. Fourteen days is not a sufficient amount of time to be infected, recover and then be virus free."

Dr. Robert Quigley, Senior Vice President and Regional Medical Director of International SOS, noted in an email to Reuters Health, "The question that remains is how great does the viral load need to be to infect another person if in fact the viral load actually decreases over time. Regardless, until this virologic feature is defined, it is clear that infected healthcare professionals (HCPs) should have two consecutive negative tests before returning to the healthcare arena where they could potentially infect a fragile patient."

"It is unclear when non-HCPs can return to the workplace after testing positive for COVID-19," he added. "This study implies that the absence of symptoms may not eliminate the risk of transmission to co-workers for up to 42 days post the onset of symptoms. Such conclusions could clearly impact our present practices of quarantine and isolation."

Dr. Taylor Heald-Sargent, an infectious diseases fellow at the Ann and Robert H. Lurie Children's Hospital of Chicago who studied coronaviruses for her PhD, commented by email that the study "confirms other reports that older patients with other medical issues are more at risk for severe disease. This could mean that this patient population has immune systems that are unable to efficiently clear infection. However, more research is needed to explore that hypothesis."

"One limitation is that (the study) focused on one geographic location," she told Reuters Health. "However, it seems likely that these results would be similar to other countries, including the United States."

SOURCE: Clinical Infectious Diseases, online April 19, 2020.