The third follow-up RT-PCR
According to the recommended CDC definitions [28], re-infection is a
probable diagnosis for the three symptomatic patients who tested
positive in the last RT-PCR test; but it is less likely in case of the
one asymptomatic patient. The third RT-PCR screening was performed 120
days after the diagnosis of COVID-19 in 32 patients (who had tested
negative on both of the previous tests). Although, the symptoms could
have been caused by re-activation of dormant infection and release of
viruses from body reservoirs, they could also be caused by re-infection.
A similar process involving latent infection of cells followed by
transcription of viral genome has also been suggested, which would
result in reactivation of the virus from a latent to a lytic stage after
a symptom-free period, causing a resurgence of COVID-19 symptoms
[39]; but the long interval between the two positive RT-PCR results
makes re-activation an unlikely diagnosis [21]. These four patients
were not significantly different from those who tested negative in terms
of past medical history or severity of the initial episode of COVID-19.
Also, we did not find any risk factors that could help distinguish
patients who are more susceptible to re-infection from those who are
not.