3.1. Clinical manifestations
Based
on the current epidemiological
investigation,
the incubation period of the COVID-19 is about 1-14 days
(Linton et al., 2020). It has been
reported that the incubation period for severe cases may be shorter than
that of the mild cases and it tended to be shorter among patients older
than 60 than those aged less than 60 years old. The most common symptoms
at onset of COVID-19 illness according to
WHO
report that was done on more than 70,000 cases in China are as
following: fever (88%), cough (68%), and fatigue (38%), dyspnea
(21.9%) (Chappell, 2020;
Pranab, Nazia, Anup, Bhabatosh, & Raman,
2020). Non-respiratory symptoms like nausea, vomiting, and diarrhea
were uncommon presentations (Luigi Angelo,
Giovanni, & Giacomo De, 2020). Infected children might appear
asymptomatic or present with fever, dry cough, and fatigue, and few
presented with gastrointestinal symptoms including abdominal discomfort,
nausea, vomiting, abdominal pain, and diarrhea
(K. Shen et al., 2020). According to the
report on “Diamond Princess”, 189 (17.9%) patients were asymptomatic
carriers (Lee, 2020), which indicated
that there exist a large number of asymptomatic individuals remain
undiscovered in the community. It is crucial to identify and isolate
asymptomatic carriers and mild patients to contain the outbreaks in
later stages.
According to the severity of symptoms,
COVID-19
can be divided into four classes: mild, moderate, severe, and critical
types (Zu et al., 2020). Mild patients
presented low-grade fever, mild fatigue or dry cough only. Moderate
patients are always characterized by fever, respiratory symptoms, and
radiographic abnormality.
The
severe patients should meet one of these criteria: A. dyspnea B.
PaO2/FiO2 <300 mmHg. C. Oxygen saturation < 93% in
ambient air (Z. Sun, Thilakavathy, Kumar,
He, & Liu, 2020). And about one-third of the severe patients may
develop into critically ill with acute respiratory distress syndrome,
septic shock, and coagulation dysfunction within a week
(Gorbalenya, 2020). According to the
recent survey conducted by the China
CDC,
80.9%
of confirmed patients were mild pneumonia cases, 13.8% were severe
cases, and 4.7% were the critical cases
(Surveillances,
2020).
3.2Laboratory
examination
In
the early stage of the COVID-19, the white blood cell count is normal or
decreased, with decreased lymphocyte count. The lymphocyte subtypes were
further analyzed and found that the count of CD3+, CD4+ and CD8+ T cell
in the severe patients was significantly lower than that of the
non-severe group (Xiaobo et al., 2020).
Some patients may present elevated levels of liver enzymes (TBIL DBIL
ALB ALT AST), lactate dehydrogenase, C-reactive protein (CRP), and
coagulation disorders (D-dimer, fibrinogen)
(D. Wang et al., 2020).
The
level of cardiac troponin I, N-terminal pro-brain natriuretic peptide
and creatinine may be increased in severe and critically ill patients,
which indicated that COVID-19 could induce myocardium, kidneys, and
liver injury directly or indirectly (Jin
et al., 2020). Critical patients often have a higher level of
inflammatory
factors such as IL2, IL6, IL7, IL10, and TNF-α
(Chaolin et al., 2020).
Chen et al. reported that elevated levels of C-reactive protein,
D-dimer, and procalcitonin were associated with severe patients compared
to non-severe patients (C. Huang et al.,
2020). Zhao et al. found that a higher level of D-dimer,
high-sensitivity cardiac troponin I, serum ferritin, lactate
dehydrogenase, and IL-6 were the independent risk factors of death
(Chaomin, 2020).
Nucleic
acid testing is the standard method for the diagnosis of COVID-19
infections (Udugama et al., 2020). Based
upon the evidence from clinical research, the
SARS-CoV-2
nucleic acids can be detected in nasopharyngeal swabs, sputum, lower
respiratory tract secretions using reverse transcription-polymerase
chain reaction (RT-PCR) method (Rothan &
Byrareddy, 2020). RT-PCR has been widely deployed in diagnostic
virology and has yielded few false-positive outcomes. However, some
research suggested that this method usually showed false-negative
results due to poor RNA stability, the quality of the kit and specimen
(Kimberly E. Hanson, 2020;
Udugama et al., 2020). Both
IgM
and IgG titers were markedly increased in nearly all patients, which was
normally considered as a transition from earlier to later period of
infection (Zhang et al., 2020).
Therefore, the combination of RT-qPCR and IgM/IgG antibody assay may be
useful for diagnosing COVID-19 and screening of SARS-CoV-2 carriers,
symptomatic or asymptomatic (Imai et al.;
Z. Li et al., 2020).