Retesting Positive for SARS-CoV-2 Doesn't Mean Infectious, Study Suggests

Troy Brown, RN

May 27, 2020

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Patients who are discharged from isolation after recovering from COVID-19 and who again test positive for SARS-CoV-2 are unlikely to be infectious, according to a report from the Korea Centers for Disease Control and Prevention (KCDC).

"There's no relapse," Laila E. Woc-Colburn, MD, DTM&H, associate professor and director of medical education, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, told Medscape Medical News. Although the disease is now known to linger and that it affects more than one system of the body, other viral diseases, such as influenza and mononucleosis, also "work that way," explained Woc-Colburn, who was not involved in the study

As of May 15, Korean researchers had identified 447 patients who again tested positive on real-time reverse transcriptase–polymerase chain reaction (RT-PCR) testing for viral RNA. Of those, 285 (63.8%) patients had undergone epidemiologic investigation and contact investigation. Among the tested individuals, 59.6% were tested for screening purposes, and 37.5% underwent testing because of their having symptoms. Almost half (44.7%) of the 284 patients who underwent investigation were symptomatic.

Data from three groups of patients from different cities showed that between 25.9% and 48.9% of patients again tested positive after they had been discharged.

Among the 226 patients who were symptomatic when their case was initially confirmed, a repeat positive test result after discharge occurred an average of 44.9 days (range, 8 – 82 days) from the date symptoms initially developed. It took an average of 14.3 days (range, 1 – 37 days) from the time of discharge to the time of the second positive test.

More than half (59.6%) of patients who tested positive a second time were tested for screening purposes, without regard to symptoms. Of those who again tested positive, 44.7% had symptoms that included cough and sore throat.

No Evidence of Infectivity

To help determine whether a positive result on a second test is associated with infectivity, the Korean researchers investigated 790 contacts of the 285 patients who tested positive a second time. Of those patients, 351 were family members, and 439 were others. Among the contacts, the researchers identified three new cases; however, for all three patients, other sources of infection were possible. These sources included religious groups or family groups in which there wre persons who were confirmed to have COVID-19.

The researchers tried to culture virus from 108 patients who tested positive a second time; all such cultures were negative.

Further, first and second serum samples were obtained from 23 patients who had tested positive a second time. Of those, 96% tested positive for neutralizing antibodies.

"Based on active monitoring, epidemiological investigation, and laboratory testing of re-positive cases and their contacts, no evidence was found that indicated infectivity of re-positive cases," the authors write.

For patients who tested positive a second time, the KCDC employed the same protocol used for patients who initially test positive. That protocol requires the patient to be isolated and to undergo further testing. However, on the basis of the current findings, the KCDC revised its protocol for managing such patients.

The agency now maintains that patients who have been discharged from isolation need no further testing and are not likely to be infective, even if they again test positive on RT-PCR assay.

Although reporting, investigation, and contact tracing of patients who again test positive will continue "for the purposes of research and investigation," the patients will no longer be regarded as "re-positive cases" but as "PCR re-detected after discharge from isolation" patients.

The authors and Woc-Colburn have disclosed no relevant financial relationships.

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