IgG Antibodies, SARS-CoV-2 Load, and Prognostic Indicators in Patients with Severe and Mild COVID-19 in Japan.

ABSTRACT

We assessed the association of severity of coronavirus disease 2019 (COVID-19) with acute respiratory syndrome coronavirus 2 (SARS-CoV-2) load, IgG antibody level, and prognostic indicators.Twenty-one patients hospitalized with COVID-19 were classified as having severe or mild disease on the basis of average respiratory rate during hospitalization (severe ≥22 breaths/min; mild <22 breaths/min). Viral load in nasopharyngeal samples, blood levels of C-reactive protein (CRP), lymphocytes, and D-dimer on admission and plasma immunoglobulin G (IgG) index on Day 7±2 after symptom onset were compared in relation to disease severity. Seven patients had severe disease and 14 had mild disease. Those with severe disease had a significantly higher IgG index (median 3.75 vs 0.56, p=0.01) and CRP (median 8.6 vs 1.0 mg/dL, p<0.001) and D-dimer levels (median 1.65 vs 0.75 µg/mL; p=0.002) and a significantly lower lymphocyte count (median 1,176 vs 666 cells/µL, p=0.005) and viral load (median 8.7×106 vs 2.3×104 copies/mL, p=0.005). Furthermore, time from symptom onset to virus disappearance was significantly longer in severe patients (median 24 vs 17 days, p=0.03). A high IgG index in the early phase of the disease was associated with severe disease and might serve as a prognostic indicator.