Some patients test positive for SARS-CoV-2 after recovery, few may be infectious
Approximately 18% of patients who recovered from COVID-19 and tested negative for the virus later tested positive, and a small number may still have been infectious, according to a study published in JAMA Internal Medicine.
“This study highlights that many patients who recovered from COVID-19 may be still positive (albeit at lower levels) for SARS-CoV-2 RNA, but only a minority of the patients may carry a replicating SARS-CoV-2 in the respiratory tract,” Flora Marzia Liotti, PhD, of the department of basic biotechnological sciences at the Catholic University of the Sacred Heart in Italy, and colleagues wrote.
Liotti and colleagues assessed real-time polymerase chain reaction (RT-PCR) nasal or oropharyngeal swab samples from patients who recovered from COVID-19 and had previously tested negative for replicative SARS-CoV-2 RNA.
The study included 176 patients who were admitted to post-acute outpatient service at a center in Rome between April 21 and June 18 after recovering from COVID-19 illness. Prior to receiving post-acute care, these patients had ended isolation precautions after they no longer had a fever for 3 days, their other symptoms had improved and they tested negative for SARS-CoV-2 RNA through RT-PCR twice within 24 hours.
Among patients included in the study, the researchers found that 18.2% (n = 32) tested positive for SARS-CoV-2 RNA after their negative tests. Of these patients, one (3.2%) had replicative SARS-CoV-2 RNA.
When retesting samples that were taken at the time of COVID-19 diagnosis among those patients who tested positive after recovery, the researchers found that all had replicative RNA.
Thirty-one of the 32 patients who tested positive after COVID-19 recovery also had positive serology results against SARS-CoV-2, in addition to 139 of the 144 patients who did not test positive after COVID-19 recovery.
Liotti and colleagues noted that the only patient who tested serologically negative was the one with replicative SARS-CoV-2 RNA after COVID-19 recovery.
Among patients who tested positive after COVID-19 recovery, the mean time from COVID-19 diagnosis to follow-up test was 48.6 days. Among those who did not test positive after recovery, the mean time to follow-up after COVID-19 diagnosis was 57.7 days.
In an editor’s note accompanying the study, Mitchell H. Katz, MD, president and CEO of NYC Health and Hospitals, noted that while the findings do not “solve the challenge of interpreting positive PCR results in recovered patients, the data help us to better understand the scope of the problem.”
To avoid unnecessary quarantines, he added that patients who recovered from COVID-19 should not undergo routine repeated PCR testing for 90 days after infection.
If patients are symptomatic and have repeated positive PCR tests, Katz wrote, this recommendation becomes more complicated. He said that while SARS-CoV-2 reinfection has been observed, it is rare.
“Until clinical laboratories have the capability to test for the reproductive capacity of coronavirus, interpretation of the epidemiologic significance of positive PCR results among recovered patients will remain challenging,” Katz wrote.