Longer Duration of SARS-CoV-2 Infection in a Case of Mild COVID-19 With Weak Production of the Specific IgM and IgG Antibodies

Abstract

Background: The relationship between SARS-CoV-2-carrying time and specific antibody production has not yet been reported in re-admitted COVID-19 patients. We reported a case of mild COVID-19 with long virus-carrying time, weak production of virus-specific IgG and IgM antibodies, and recurrence of positive SARS-CoV-2 RNA in stool specimens after discharge. Case Presentation: A 27-year-old male was diagnosed as COVID-19 after returning to Meizhou from Wuhan. Despite extremely mild symptoms, the patient was hospitalized for 24 days because of persistent positive SARS-CoV-2 RNA detection. Three days after recovery discharge, he was hospitalized again for 7 days due to a recurrence of the positive SARS-CoV-2 RNA result, while in a good physical condition. Serological assay, using a fluorescent immunochromatography detection kit specific to SARS-CoV-2, showed that SARS-CoV-2-specific IgM antibodies were undetectable and IgG antibodies were very low on day 8 after onset; both of the antibodies seemingly reached top concentrations on day 15 (just a 6-fold increase of the IgG titer), and then decreased, remaining relatively stable from day 25 after onset until discharge. The production of the IgM and IgG targeting SARS-CoV-2 in this very mild case was much lower than that in a severe case of COVID-19 during the same hospitalizing period, and the latter was used as a control. Conclusion: Mild COVID-19 patients could carry SARS-CoV-2 for a long time, which may be related to the weak production of the virus-specific IgG and IgM. Recurrence of positive SARS-CoV-2 RNA could occur in mild COVID-19 possibly due to intermittent virus shedding, so strict quarantine and health surveillance should be taken for all discharged COVID-19 patients to prevent a potential virus spread.

Keywords: SARS-CoV-2; case report; mild COVID-19; persistent infection; virus-specific antibody response.

Figure 1

The dynamics of the throat swab and stool sample test of SARS-CoV-2 RNA, body temperature, blood cell counts, and medications of a mild COVID-19 during hospitalization. Antiviral medication: Kaletra, Arbidol, Darunavir, and Chloroquine. Supplementary medication: Thymalfasin and IVIG. IVIG, intravenous immunoglobulin; WBC, white blood cell count (3.5–9.5 × 10⁹/L); LYMPH, lymphocytes (1.1–3.2 × 10⁹/L).

Figure 2

Serological assays of IgG and IgM specific to SARS-CoV-2 of a mild COVID-19 patient, with a severe COVID-19 case as the control. The presence and concentration of IgM and IgG targeting SARS-CoV-2 were measured using a fluorescent immunochromatography detection kit specific to the IgM and IgG against SARS-CoV-2. The cutoff values for IgG and IgM detection were 0.057 and 0.067, respectively.