Demographic and clinical characteristics of asymptomatic,
presymptomatic, and symptomatic COVID-19 patients
Of the initial 3,046 COVID-19 patients who were screened for study
inclusion, 66 were excluded, including those who were readmitted (n=11),
had negative nucleic acid test results (n=19), or had missing data on
the degree of illness severity (n=36). Thus, 2,980 patients were
included in the study: 39, 34, and 2,907 asymptomatic, presymptomatic
(non-severe, n=9, 26%; severe, n=25, 74%), and symptomatic
(non-severe, n=1,385, 58%; severe, n=1,522, 52%) patients,
respectively (Fig. 1). To ensure the even distribution of confounders
among the study groups, baseline correction was performed (16), and we
obtained a sample of 1,751 symptomatic COVID-19 patients, of whom 907
(51.8%) and 844 (48.2%) had non-severe and severe illness,
respectively (Fig. 2A). The commonest symptoms in symptomatic patients
from disease onset to hospital admission were fever (n=2,178, 75%) and
cough (n=2,097, 72%). Shortness of breath, respiratory distress, and
fatigue were observed in 1,320 (45%), 1,157 (40%), and 681 (23%)
patients, respectively. Less common symptoms in symptomatic COVID-19
patients included muscle soreness (n=118, 4%), diarrhea (n=66, 2%),
headache (n=18, 1%), dizziness (n=26, 1%), nausea (n=21, 1%), and
vomiting (n=21, 1%). Of note, respiratory failure, a sign of severe
illness, was observed in only 36 symptomatic COVID-19 patients with
pneumonia (<1%; Table S1).
The median age of the patients was 60 years (IQR: 50–68 years), and
there were no significant differences in age and sex among the three
groups. Basic diseases (such as hypertension and diabetes) were detected
in asymptomatic (15.38%), presymptomatic (20.58%), and symptomatic
(16.44%) COVID-19 patients (Fig. 2B, Table S1). Surprisingly, those in
the presymptomatic severe group had higher rates of admission to the
intensive care unit (ICU; 8.3% vs 3.3%, P -value=0.2, Fig. 2C)
and mortality (4% vs 1.8%, P -value=0.37, Fig. 2D) than patients
in the symptomatic severe group. Additionally, there were no significant
differences in viral RNA load among asymptomatic, presymptomatic, and
symptomatic patients (Fig. 2E). It indicated that infected persons may
still transmit the virus to others and should be quarantined, regardless
of symptoms(6). The levels of specific immunoglobulin G (IgG) and
immunoglobulin M (IgM) antibodies against SARS-CoV-2 were significantly
higher in symptomatic patients than in asymptomatic and presymptomatic
patients (Fig. 2F), indicating that patients might have variable
antibody reactions despite similar viral RNA loads.