GUWAHATI, Nov 27 - Testing positive for the second time cannot be termed as re-infection for SARS-CoV-2, as there are chances that the person might have harboured the virus as a temporary bystander in droplet particles in their nasal cavity which got detected by the highly sensitive Real Time RT-PCR but it failed to cause a clinical or subclinical infection, a new study has suggested.
The study carried out by Dr Gayatri Gogoi, Dr Mandakini Das, Dr Biswajyoti Borkakoty, Dr Mondita Borgohain and Dr Anup Das, investigated suspected cases of SARS-CoV-2 re-infection among eight health-care workers involved in COVID-19 healthcare duty in Dibrugarh. The research team is from Assam Medical College and Hospital and ICMR-Regional Medical Research Centre, Lahowal.
All eight cases were asymptomatic in first episode of infection with a CT value above 30 and were non-reactive for SARS-CoV-2 IgG Ab � which means they had low viral load and did not develop antibodies.
The second episode was symptomatic and marginally severe in some cases with CT value less than 30 and with positive SARS-CoV-2 Ab titer. �This may suggest that in the first episode, SARS-CoV-2 in low amount might have been harboured transiently as bystander in droplet particles before being expelled from the nasal cavity which can be detected by the highly sensitive real time RT-PCR test,� Dr Gayatri Gogoi said.
She said that a person with weakened immune system may fail to develop antibody response but it is most unlikely in these eight cases as they are young individuals with no prior history of any disease.
Further, the antibody titer of the persons after 28 days of suspected second positive test showed positive antibody response with ISR (immune status ratio) as high as 12 to 15.
�There is a probability that a fraction of the asymptomatic cases may not evoke an immune response (antibody response) against the virus and they may remain susceptible to infection on further exposure. Therefore, asymptomatic SARS-CoV-2 positive cases need to be monitored for Ab titer (antibody) as they may fail to develop immunity against the virus and might again get re-infected on further exposure,� Dr Gogoi said.
The study has suggested routine surveillance of SARS-Cov-2 antibody testing for healthcare workers to ascertain their immune status as they are the frontline workers of managing COVID-19 patients and are highly exposed to the virus.
Another observation was that in two cases, both were asymptomatic in first episode and mildly symptomatic in the suspected second episode. They failed to develop any immune response even after the suspected second positive test of SARS-COV-2. �The SARS-CoV-2 antibody test was negative in both episodes. The reason for negative result might be that they were false positive in both the episodes,� the study further noted.
The study has been sent to the Indian Journal of Pathology and Oncology for publication.
