Molecular and serological characterization of SARS-CoV-2 infection among COVID-19 patients

Abstract

Background: SARS-CoV-2 is a novel coronavirus and the cause of COVID-19. More than 80% of COVID-19 patients exhibit mild or moderate symptoms. In this study, we investigated the dynamics of viral load and antibodies against SARS-CoV-2 in a longitudinal cohort of COVID-19 patients with severe and mild/moderate diseases.

Methods: Demographic and clinical information were obtained. Serial samples of blood, nasal and pharyngeal and anal swabs were collected at different time points post-onset. SARS-CoV-2 RNA and anti-SARS-CoV-2 antibodies were measured by qRT-PCR and immunoassays, respectively.

Results: Respiratory SARS-CoV-2 RNA was detectable in 58.0% (58/100) COVID-19 patients upon admission and lasted for a median of 13 days post-onset. In addition, 5.9% (1/17) and 20.2% (19/94) of the blood and anal swab specimens were positive for SARS-CoV-2 RNA, respectively. Anal viral RNA was more frequently detected in the patients who were positive for viral RNA in the respiratory samples upon admission. Specific anti-SARS-CoV-2 antibody developed within two weeks after onset, reached peak approximately 17 days post-onset and then maintained at relatively high level up to 50 days we analyzed in most patients. However, the levels of antibodies were variable among the patients. High titers of antibodies appeared to be associated with the severity of the disease. Furthermore, viral proteins from different sources showed significant difference of serological sensitivity especially during the first week post-onset.

Conclusions: Our results indicate rapid clearance or self-elimination of viral RNA in about half of the COVID-19 patients upon admission. Viral RNA shedding of SARS-CoV-2 occurred in multiple tissues including the respiratory system, blood, and intestine. Variable levels of specific anti-SARS-CoV-2 antibody may be associated with disease severity. These findings have shed light on viral kinetics and antibody response in COVID-19 patients and provide scientific evidence for infection control and patient management.

Keywords: Anti-SARS-CoV-2 antibodies; COVID-19; SARS-CoV-2; Viral RNA.

Fig. 1

Temporal profiles of anti- SARS-CoV-2 antibodies. Serum IgG (A), IgM (B) and IgA (C) against SARS-CoV-2 NP were ascertained by LISA in 98, 15 and 15 COVID-19 patients, respectively. Each patient is represented by the lines labelled with different colors. The linear relationship between the luciferase counts of anti-NP and the amount of antibody was presented in panel D. Patient #NCP13 (panel E) and 15 (panel F) were negative for viral RNA in throat (red), blood (blue) and anal swabs (green) by qRT-PCR with cutoff value of 40 cycles (black dash line), and for antibody against SARS-CoV-2 NP (brown), RBD (pink) and S1 subunit (yellow) by ELISA. LISA = luciferase immunosorbent assay. ELISA = enzyme linked immunoassay. NP = nucleocapsid proteins. RBD = receptor-binding domain. S1 = spike protein S1 subunit. S/CO = sample/cutoff. OD450 = optical density at 450 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Temporal profiles of viral RNA and anti-SARS-CoV-2 antibodies for 7 COVID-19 patients with extended viral RNA shedding. Viral RNA in throat (red), blood (blue) and anal swabs (green) was ascertained by qRT-PCR with cutoff value of 40 cycles (black dash line). Serum antibody against SARS-CoV-2 NP (brown), RBD (pink) and spike protein S1 subunit (yellow) was detected by ELISA. Each panel represents each patient. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Temporal profiles of anti-SARS-CoV-2 antibodies among COVID-19 patients. ELISA was adapted for detecting serum IgG antibody against SARS-CoV-2 S1 protein from East-Mab Biomedical Technology, Jiangsu (panel A, N = 98) and Medical institute of oriental ocean, Beijing (panel B, N = 15), and against RBD protein from East-Mab Biomedical Technology, Jiangsu (panel C, N = 98) and Vendor C (panel D, N = 15), as well as NP from Hanrui Biology, Nanjing (panel E, N = 98). Each patient was represented by the line labelled with different color. Dash lines indicate ELISA cutoff values. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)