key: cord-275250-ilmgy7ce
authors: Xia, Yong; Hong, Honghai; Feng, Yao; Liu, Meiling; Pan, Xingfei; Chen, Dexiong
title: Dynamics of antibodies to SARS-CoV-2 in a case with SARS-CoV-2 infection
date: 2020-05-17
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2020.05.042
sha: 
doc_id: 275250
cord_uid: ilmgy7ce

nan

To the Editor: COVID-19, caused by SARS-CoV-2, has been worldwide reported [1] . To date, the diagnosis of SARS-CoV-2 infection is dependent on detecting nucleuic acid of SARS-CoV-2 by qRT-PCR or by next-generation sequencing (NGS) [2] . In clinical practice, some highly suspected cases had negative results for nucleic acid of SARS-CoV-2 [3] . In the present study, we evaluated whether detecting antibodies to SARS-CoV-2 could be as a diagnostic marker for SARS-CoV-2 infection.

A 29-year-old woman, had fever, no cough and fatigue on Feb 9, 2020. On Feb 12, she was referred to our hospital, because her mother was diagnosed as COVID-19. Nasopharyngeal swabs and anal swabs were collected and were assayed nucleic acid of SARS-CoV-2. Peripheral blood samples were collected from the patient on Feb 14, 17, and 20, respectively. Four IgG/IgM antibodies detection Kits (manufactured by Company A, Guangzhou Darui Biotechnology Co., Ltd; Company B, Zhuhai Livzon Diagnostics Inc.; Company C, Beijing Hotgen Biotech Co., Ltd;

Company D, Shenzhen New Industries Biomedical Engineering Co., Ltd., respectively) were used to detect antibodies to SARS-CoV-2. Colloidal gold method was used in Kits A, B and C, while chemiluminescence method was used in Kit D. Kit C was coated with spike (S) and nucleocapsid (N) proteins of SARS-CoV-2. Only N protein was coated in Kits A, B and D, respectively.

Blood routine on admission showed lymphocyte counts were not lowered. On Feb 15, chest CT images showed typical characteristics of COVID-19. Nasopharyngeal swabs and anal swabs were collected six times, and both were negative for SARS-CoV-2. Furthermore, none of SARS-CoV-2 and other pathogens was found in the collected sputum samples tested by NGS.

As shown in Table 1 , on Feb 14, reactivity to IgM/ IgG antibodies was very weak and invisible to the naked eye by using Kit A, C. Reactivity to IgM antibody was positive and visible to the naked eye by using Kit B. IgM and IgG antibodies had been assayed by using Kit D, and IgM and IgG antibody levels were 0.62 AU/mL, 2.41 AU/mL, respectively (normal IgM and IgG <1.1 AU/mL). On Feb 17, reactivity to IgG antibody was significantly positive, but reactivity to IgM antibody was still weak by using Kit A. Reactivity to IgM antibody was obviously positive by using Kit B. IgM and IgG antibody levels were 0.74 AU/mL, 6.90 AU/mL, respectively. However, none of antibodies was detected by using Kit C. On Feb 20, reactivity to IgM and IgG was higher than that detected by using Kit A on Feb 17. Reactivity to IgM was also higher than that detected by using Kit B and C on Feb 17, respectively. Furthermore, IgM and IgG antibody levels were 0.92 AU/mL, 13.46 AU/mL, respectively, which was higher than that detected by using Kit D on Feb 17 (Figure 1 ).

In the present study, IgG/IgM antibodies to specific proteins of SARS-CoV-2 were found in blood sample of the patient and gradually increased. Because COVID-19 is a newly emerged disease, the patient with either positive for IgM or IgG antibodies to SARS-CoV-2 should be considered as the presence of SARS-CoV-2 infection. So we believe that positive for IgM or IgG antibodies could be a marker to diagnosis of SARS-CoV-2 infection no matter the results of testing nucleic acid.

Dynamically detecting IgG and IgM antibodies to virus was very important to the diagnosis of viral infections [4, 5] . Our results showed that IgM or IgG antibodies detected by different Kit were gradually increased (Table 1, Figure 1 ). This implied that antibody to SARS-CoV-2 actually existed in the patient. Although IgM antibody level detected by Kit D was increased, it was still Note: N, nucleocapsid proteins of SARS-CoV-2; S, spike proteins of SARS-CoV-2.

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