Shedding of SARS-CoV-2 Virus in COVID-19 Patients and Neutralizing Antibody Level

Abstract

The coronavirus disease 2019 (COVID-19) turned into a pandemic shortly after emerging in Decem- ber 2019, in the city of Wuhan, China. In this study, it was aimed to investigate the presence of severe acute respiratory system coronavirus-2 (SARS-CoV-2) RNA in various clinical samples and the scattering profile of the virus and the variation of anti-SARS-CoV-2 IgG and neutralizing antibody levels over time in infected patients during and after the period of COVID-19 disease. The study included COVID-19 patients from the community (CCP) (n= 47) (May-June 2020) and healthcare workers (HCWP) (n= 30) (November-December 2020). To investigate the presence of SARS-CoV-2 in clinical samples, oropharynx (OF), nasopharynx (NF), sputum, stool, blood and urine samples were taken from the CCP group on days 0, 3, 7, 14 and 28. For the detection of anti SARS-CoV-2 IgG and neutralizing antibodies serum samples were taken from the CCP group on days 0, 3, 7, 14, 28, 60, 90 and 120 and on days 14, 28, 60, 90, 120 and 150 from HCWP group. Virus RNA was detected by reverse transcription polymerase chain reaction (RT-PCR), anti SARS-CoV-2 IgG antibody levels by enzyme-linked immunosorbent assay (ELISA), neutra- lizing antibody levels (NAb) by cell culture neutralization and representative neutralization test (sVNT) methods. With the onset of the vaccination program in our country, 11 of the HCWP group patients had SARS-CoV-2 vaccine after the second month serum samples were taken, the remaining HCWP group patients did not get vaccinated during the study period. SARS-CoV-2 RNA was detected with the highest rates in NF (100%), stool (65.8%), sputum (45.7%), OF (41.3%), blood (5.3%), and urine (2.2%) samp- les, respectively. It was found that viral shedding continued for 14 days in respiratory tract samples and up to 60 days in stool samples, and no virus was detected in blood samples after the third day. It was observed that the viral load was highest at the time of diagnosis in both upper and lower respiratory tract samples, peaking on the seventh day in stool samples and following an irregular course throughout the disease. Anti-SARS-CoV-2 IgG antibody positivity was found in 41.4% of CCP group patients on the first day of diagnosis, and seroconversion was observed in all patients at the fourth month. During the study period, seropositivity was detected in only 82.1% of the patients in the HCWP group. It was observed that the IgG antibody levels peaked at the 7th day in the CCP group patients and at the third month in the HCWP group patients (S/Co: 9.6 and 2.8, respectively). Anti-SARS-CoV-2 IgG antibody levels detected in the CCP group were found to be significantly higher than the HCWP group (p< 0.05). At the end of the first month, NAb was detected in all (100%) patients in the CCP group. It was found that NAb titers peaked (1/256) on the 28th day and showed a decreasing trend from the second month. NAb median titers were observed to peak earlier in the severe HCWP group (14 days in the severe group, 28 days in the mild group, p> 0.05). It was observed that 6 (26.1%) of HCWP group patients had low, 11 (47.8%) moderate, 6 (26.1%) high titers of representative NAb. The distribution of representative NAb levels by vaccine status was examined and no statistically significant difference was found (p= 0.400, p= 0.077 and p= 0.830, respectively). As a result; SARS-CoV-2 RNA was detected in many samples such as sputum, stool, blood and urine, and it was observed that viral shedding in stool samples could continue for months. Anti-SARS-CoV-2 IgG antibody positivity was observed in most of the patients in the fourth month, and it was found that the antibody titers decreased after the third month. It was determined that protective antibody levels continued in the fourth month. These findings are important in vaccination strategies and in the fight against the pandemic. However, considering the emergence of new mutant forms of the virus in today's conditions where the pandemic continues, more detailed and comprehensi- ve studies are needed for viral shedding and antibody titer studies.