Introduction
In
December 2019, an outbreak of unidentified pneumonia
characterized
by fever, dry cough, and fatigue happened in the Huanan Seafood
Wholesale Market, in Wuhan, Hubei, China(J.
F.-W. Chan, Yuan, Kok, To, Chu, Yang, Xing, Liu, Yip, & Poon, 2020;
Chen, W, G, & F, 2020;
Hongzhou, W, & Yi-Wei, 2020). With the
spread of the disease,
the
numbers of infected patients increased substantially which has become
the most challenging health emergency in China and even all over the
world. Sequence analysis of the coronavirus obtained from 5 patients in
Wuhan has shown a structure typical to that of other coronaviruses such
as SARS coronavirus and MERS coronavirus(N.
Chen et al., 2020; Sohrabi et al.,
2020). It also revealed that the new coronavirus has the smallest
genetic distance from bat coronavirus, and about 80% similarity with
SARS-CoV, and 50% similarity with
MERS-CoV(P. Sun, Lu, Xu, Sun, & Pan,
2020). Thereafter, the coronavirus was designated as SARS-CoV-2 and the
infected disease was named Coronavirus Disease 2019 (COVID-19) by the
World Health Organization (WHO)(Li-Li et
al., 2020; Sohrabi et al., 2020;
Zhu et al., 2020). In addition, the
nosocomial infection was found on January 20, 2020 which suggested that
COVID-19
can be transmitted from human to human.
As of April 13, 2020 a total of
83696
cases have been confirmed in China and 1837079 cases reported in 209
countries outside of China. Due to the effective prevention and control
measures in China, about 93.5% patients were cured and discharged and
the existing confirmed cases decreased to 2083. However, the confirmed
cases are still
growing
rapidly in foreign countries including United State, Italy, Spain,
Germany and France, and United State has been particularly affected.
With the further recognition of
COVID-19
and experience in diagnosis and treatment cumulates, the National Health
Commission (NHC) released a consensus about the Diagnosis and Treatment
Scheme for Novel Corona Virus Pneumonia which put forward new standard
for diagnosis and treatment. The present article is to provide a review
of the characteristics of the COVID-19 including the epidemiology,
clinical features, pathological changes, diagnosis, treatment, and the
experience of prevention and control measures for this disease.
1. Epidemiology ofCOVID-19
Since
December 2019, the first 27 case of unidentified pneumonia with a
history of exposure in the Huanan Seafood Market were reported by the
Wuhan Municipal Health Commission(Ashour,
Elkhatib, Rahman, & Elshabrawy, 2020).
On
Jan 11, 2020, the pathogen of the pneumonia was initially confirmed as a
new coronavirus. On
January
20, the human-to-human transmission and nosocomial infection were
official
confirmed firstly(J. F.-W. Chan, Yuan, Kok,
To, Chu, Yang, Xing, Liu, Yip, Poon, et al.,
2020).
And the same day, 4 confirmed cases of 2019-nCoV have been reported from
three countries outside of China including Thailand (2 cases), Japan (1
case) and the Republic of Korea (1 case). With the epidemic further
expanding,
daily
confirmed case increased to 3892, and
then
fluctuated to 2022 on February 11. Because of the improvement of
diagnosis standard for confirmed cases,
there
were 14109 new clinically diagnosed cases were reported on February 12,
2020. Since then, the number of daily emerging cases gradually declined.
However, the daily emerged cases were increased rapidly in abroad. Data
released on February 25, 2020
showed
foreign countries had overtaken China in confirmed cases per day for the
first time (Figure.1) . Up to April 13, 2020, there were 83696
confirmed cases in China, and 1837079 cases were totally confirmed in
209 countries outside of China (Figure. 2, 3 ).
From
November 2019 to April 13, 2020,
the
number of cumulative deaths caused by the COVID-19 was 119138, and the
overall case-fatality rate (CFR) was 6.20 % which was lower than that
of the SARS (9.60%) and MERS
(34.4%) (Figure.4,
Table.1).
The
transmission of infectious diseases must rely on three requirement
conditions: sources of infection, routes of transmission, and
susceptible hosts(Evans, 2013;
Keeling & Rohani, 2011). A growing body
of scientific evidence suggests that COVID-19 is a zoonotic disease as
with SARS and MERS,
and
originated from wild bat(Evans, 2013).
And pangolins and snakes were likely to be intermediate hosts of
SARS-CoV-2. According to the Diagnosis and Treatment Scheme for Novel
Corona Virus Pneumonia (Trial) 7th Edition, close contact with
symptomatic cases and asymptomatic cases with silent infection are the
main transmission routes of 2019-nCoV infection. It
suggested
that SARS-CoV-2 can be transmitted through respiratory aspirates,
droplets, contacts, and digestive tract transmission remained to be
confirmed(Peng et al., 2020).
Vertical
transmission was sporadically reported in some media but not yet
proved(Aldohyan et al., 2019). Reports
showed that the basic reproductive values (R0) of COVID-19 were
calculated between 2 and 3.5, which means that one patient could
transmit the disease to two to three other people. Therefore, SARS-CoV-2
appears to be more infectious than SARS-CoV or MERS-CoV based on R0
values at the early stage of this
outbreak(Ying, A, Annelies, & Joacim,
2020)(Table.1 ). Similar to SARS and MERS, nosocomial
transmission was a severe problem or even worse. COVID-19 had posed a
difficult challenge to healthcare facilities from both the impact of
healthcare-associated transmission and the resource burden of
controlling and preventing further
spread.
It has been reported that a total of 3019 health workers were infected,
accounting for 4.17% of total cases. Unfortunately, 14.8% of confirmed
cases were classified as severe or critical and 5 deaths were observed.
In terms of susceptible populations, people are generally susceptible to
COVID-19 regardless of age or
gender(Surveillances, 2020). 86.6 % of
all patients were aged from 30 to79, and the median age of the patients
was 47 years. The elderly and those with underlying chronic diseases are
more likely to become severe cases(Shen et
al., 2020).
2.The
etiology of COVID-19
Coronavirus
is comprised of
single-stranded
positive RNA virus that belongs to an order Nidovirales, family
Coronaviridae, and
subfamily
Orthocoronavirinae (Jie, Fang, &
Zheng-Li, 2019).
Coronavirus
can be divided to four genera: α-, β-, γ-, δ-coronavirus according to
the characteristics of serotype and
genome(P, Xin, P, & Y, 2019). Genome
sequences analysis showed that the coronavirus is a new type of
coronavirus (SARS-CoV-2) and belongs to beta-CoV
strain(Li-Li et al., 2020;
Ren et al.,
2020).
A
recent study demonstrated that
SARS-CoV-2
can survive in human respiratory epithelial cells for 96 hours in
vitro(Huang et al.,
2020).
Current studies have revealed that SARS-CoV-2 shared the same receptors
with SARS-CoV and MERS-CoV for
invading
the host cells(Huang et al., 2020). And
the spike (S) protein serves as the main antigenic proteins for binding
to angiotensin-converting enzyme 2 (ACE2) receptor and mediates
subsequent fusion between the envelope and host cell membranes to aid
viral entry into the host cell(X. Xu et
al., 2020). In fact,
SARS-CoV-2
also
shared
the same physical and chemical characteristics with SARS-CoV and
MERS-CoV.
Coronaviruses
are sensitive to ultraviolet ray and heat. And it can be killed easily
by exposed to 56 ℃ for 30 mins, 75% ethanol, chlorine disinfectant,
peracetic acid and chloroform(Duan et al.,
2003).
3. Clinical characteristics ofCOVID-19