Distinguishing repeated polymerase chain reaction positivity from re-infections in COVID-19

Possibility of reinfection with SARS-CoV-2 changes our view on herd immunity and vaccination and can impact worldwide quarantine policies. We performed real-time polymerase chain reaction (RT-PCR) follow-up studies on recovered patients to assess possible development of reinfections and re-positivity.

During a 6-month period, 202 PCR-confirmed recovering COVID-19 patients entered this study. Follow-up RT-PCR tests and symptom assessment were performed 1 month after the initial positive results. Patients who tested negative were tested again 1 and 3 months later. The serum IgG and IgM levels were measured in the last follow-up session.

In the first two follow-up sessions, 82 patients continued their participation, of which four patients tested positive. In the second follow-up 44 patients participated, three of whom tested positive. None of the patients who tested positive in the first and second follow-up session were symptomatic. In the last session, 32 patients were tested and four patients were positive, three of them were mildly symptomatic and all of them were positive for IgG.

A positive RT-PCR in a recovering patient may represent reinfection. While we did not have the resources to prove reinfection by genetic sequencing of the infective viruses, we believe presence of mild symptoms in the three patients who tested positive over 100 days after becoming asymptomatic, can be diagnosed as reinfection. The immune response developed during the first episode of infection (e.g., IgG or T-cell mediated responses that were not measured in our study) may have abated the symptoms of the reinfection, without providing complete protection.