Zunyou Wu, MD,
PhD1; Jennifer
M. McGoogan, PhD1 Author
Affiliations Article Information JAMA. Published online February
24, 2020. doi:10.1001/jama.2020.2648 中文 (chinese)
The Chinese Center for Disease Control and
Prevention recently published the largest case series to date of coronavirus
disease 2019 (COVID-19) in mainland China (72 314 cases, updated through
February 11, 2020).1 This Viewpoint summarizes key findings from this report
and discusses emerging understanding of and lessons from the COVID-19 epidemic.
Epidemiologic Characteristics of the COVID-19
Outbreak
Among a total of 72 314 case records (Box),
44 672 were classified as confirmed cases of COVID-19 (62%; diagnosis based on
positive viral nucleic acid test result on throat swab samples), 16 186 as
suspected cases (22%; diagnosis based on symptoms and exposures only, no test
was performed because testing capacity is insufficient to meet current needs),
10 567 as clinically diagnosed cases (15%; this designation is being used in
Hubei Province only; in these cases, no test was performed but diagnosis was
made based on symptoms, exposures, and presence of lung imaging features
consistent with coronavirus pneumonia), and 889 as asymptomatic cases (1%;
diagnosis by positive viral nucleic acid test result but lacking typical
symptoms including fever, dry cough, and fatigue).1
·
Key Findings From the Chinese Center for Disease
Control and Prevention Report
·
72 314
Cases (as of February 11, 2020)
o
Confirmed
cases: 44 672 (62%)
o
Suspected
cases: 16 186 (22%)
o
Diagnosed
cases: 10 567 (15%)
o
Asymptomatic
cases: 889 (1%)
·
Age
distribution (N = 44 672)
o
≥80
years: 3% (1408 cases)
o
30-79
years: 87% (38 680 cases)
o
20-29
years: 8% (3619 cases)
o
10-19
years: 1% (549 cases)
o
<10
years: 1% (416 cases)
·
Spectrum
of disease (N = 44 415)
o
Mild:
81% (36 160 cases)
o
Severe:
14% (6168 cases)
o
Critical:
5% (2087 cases)
·
Case-fatality
rate
o
2.3%
(1023 of 44 672 confirmed cases)
o
14.8%
in patients aged ≥80 years (208 of 1408)
o
8.0%
in patients aged 70-79 years (312 of 3918)
o
49.0%
in critical cases (1023 of 2087)
·
Health
care personnel infected
o
3.8%
(1716 of 44 672)
o
63%
in Wuhan (1080 of 1716)
o
14.8%
cases classified as severe or critical (247 of 1668)
o
5
deaths
Most case patients were 30 to 79 years of age
(87%), 1% were aged 9 years or younger, 1% were aged 10 to 19 years, and 3%
were age 80 years or older. Most cases were diagnosed in Hubei Province (75%)
and most reported Wuhan-related exposures (86%; ie, Wuhan resident or visitor
or close contact with Wuhan resident or visitor). Most cases were classified as
mild (81%; ie, nonpneumonia and mild pneumonia). However, 14% were severe (ie,
dyspnea, respiratory frequency ≥30/min, blood oxygen saturation ≤93%, partial
pressure of arterial oxygen to fraction of inspired oxygen ratio <300,
and/or lung infiltrates >50% within 24 to 48 hours), and 5% were critical
(ie, respiratory failure, septic shock, and/or multiple organ dysfunction or
failure) (Box).1
The overall case-fatality rate (CFR) was 2.3%
(1023 deaths among 44 672 confirmed cases). No deaths occurred in the group
aged 9 years and younger, but cases in those aged 70 to 79 years had an 8.0%
CFR and cases in those aged 80 years and older had a 14.8% CFR. No deaths were
reported among mild and severe cases. The CFR was 49.0% among critical cases.
CFR was elevated among those with preexisting comorbid conditions—10.5% for
cardiovascular disease, 7.3% for diabetes, 6.3% for chronic respiratory disease,
6.0% for hypertension, and 5.6% for cancer. Among the 44 672 cases, a total of
1716 were health workers (3.8%), 1080 of whom were in Wuhan (63%). Overall,
14.8% of confirmed cases among health workers were classified as severe or
critical and 5 deaths were observed.1
COVID-19 rapidly spread from a single city to
the entire country in just 30 days. The sheer speed of both the geographical
expansion and the sudden increase in numbers of cases surprised and quickly
overwhelmed health and public health services in China, particularly in Wuhan
City and Hubei Province. Epidemic curves reflect what may be a mixed outbreak
pattern, with early cases suggestive of a continuous common source, potentially
zoonotic spillover at Huanan Seafood Wholesale Market, and later cases
suggestive of a propagated source as the virus began to be transmitted from
person to person (Figure 1).1
Figure 1.
Epidemic Curve of the Confirmed Cases of
Coronavirus Disease 2019 (COVID-19)
Daily numbers of confirmed cases are plotted
by date of onset of symptoms (blue) and by date of diagnosis (orange). Because,
on retrospective investigation, so few cases experienced illness in December,
these cases are shown in the inset. The difference between the cases by date of
symptom onset curve (blue) and the cases by date of diagnosis curve (orange)
illustrates lag time between the start of illness and diagnosis of COVID-19 by
viral nucleic acid testing. The graph's x-axis (dates from December 8, 2019, to
February 11, 2020) is also used as a timeline of major milestones in the
epidemic response. The first few cases of pneumonia of unknown etiology are
shown in blue boxes on December 26 (n = 4) and 28-29 (n = 3). Most other cases
that experienced onset of symptoms in December were only discovered when
retrospectively investigated. Major epidemic response actions taken by the
Chinese government are shown in brown boxes. The normally scheduled Lunar New
Year national holiday is shown in light yellow, whereas the extended holiday
during which attendance at school and work was prohibited (except for critical
personnel such as health workers and police) is shown in dark yellow. This
figure was adapted with permission.1 CDC indicates Chinese Center for Disease Control and
Prevention; HICWM, Hubei Integrated Chinese and Western Medicine; 2019-nCoV,
2019 novel coronavirus; WHO, World Health Organization.
Comparison of COVID-19 With SARS and MERS
The current COVID-19 outbreak is both similar
and different to the prior severe acute respiratory syndrome (SARS; 2002-2003)
and Middle East respiratory syndrome (MERS; 2012-ongoing) outbreaks. SARS was
initiated by zoonotic transmission of a novel coronavirus (likely from bats via
palm civets) in markets in Guangdong Province, China. MERS was also traced to
zoonotic transmission of a novel coronavirus (likely from bats via dromedary
camels) in Saudi Arabia. All 3 viral infections commonly present with fever and
cough, which frequently lead to lower respiratory tract disease with poor
clinical outcomes associated with older age and underlying health conditions.
Confirmation of infection requires nucleic acid testing of respiratory tract
samples (eg, throat swabs), but clinical diagnosis may be made based on
symptoms, exposures, and chest imaging. Supportive care for patients is
typically the standard protocol because no specific effective antiviral
therapies have been identified.
The World Health Organization (WHO) declared
the SARS outbreak contained on July 5, 2003. A total of 8096 SARS cases and 774
deaths across 29 countries were reported for an overall CFR of 9.6%. MERS is
still not contained and is thus far responsible for 2494 confirmed cases and
858 deaths across 27 countries for a CFR of 34.4%. Despite much higher CFRs for
SARS and MERS, COVID-19 has led to more total deaths due to the large number of
cases. As of the end of February 18, 2020, China has reported 72 528 confirmed
cases (98.9% of the global total) and 1870 deaths (99.8% of the global total).
This translates to a current crude CFR of 2.6%. However, the total number of
COVID-19 cases is likely higher due to inherent difficulties in identifying and
counting mild and asymptomatic cases. Furthermore, the still-insufficient
testing capacity for COVID-19 in China means that many suspected and clinically
diagnosed cases are not yet counted in the denominator.2 This uncertainty in the CFR may be reflected by the
important difference between the CFR in Hubei (2.9%) compared with outside
Hubei (0.4%).1,2 Nevertheless, all CFRs still need to be interpreted with
caution and more research is required.
Most secondary transmission of SARS and MERS occurred
in the hospital setting. Transmission of COVID-19 is occurring in this context
as well—3019 cases have been observed among health workers as of February 11,
2020 (of whom there have been 1716 confirmed cases and 5 deaths).1 However, this is not a major means of COVID-19 spread.
Rather, it appears that considerable transmission is occurring among close
contacts. To date, 20 provinces outside of Hubei have reported 1183 case
clusters, 88% of which contained 2 to 4 confirmed cases. Of note, 64% of
clusters documented thus far have been within familial households (Chinese
Center for Disease Control and Prevention presentation made to the WHO
Assessment Team on February 16, 2020). Thus, although COVID-19 seems to be more
transmissible than SARS and MERS, and many estimates of the COVID-19
reproductive number (R0) have already been published, it is still
too soon to develop an accurate R0 estimate or to assess the
dynamics of transmission. More research is needed in this area as well.
Response to the COVID-19 Epidemic
Since 2003, the Chinese government has
improved its epidemic response capacity. Some of these efforts are evident in
the response to COVID-19 (Figure 2). For example, in the 2002-2003 SARS outbreak, 300 cases and 5
deaths already had occurred by the time China reported the outbreak to the WHO,
whereas in the COVID-19 outbreak, only 27 cases and zero deaths had occurred
when the WHO was notified (January 3, 2020) (Figure 2). From the time of WHO notification, 2 months elapsed before
SARS-CoV was identified compared with only 1 week from the time of WHO
notification until 2019-nCoV was identified.
Figure 2.
Timeline Comparing the Severe Acute
Respiratory Syndrome (SARS) and Coronavirus Disease 2019 (COVID-19) Outbreaks
The timeline of events for the SARS outbreak
(left) from first case to final worldwide containment. The timeline of events
for the COVID-19 outbreak (right) from the onset of symptoms for the first case
on December 8, 2019, to status on February 20, 2020. Over the course of the
first 2 months, more than 70 000 cases have been confirmed and many more are
suspected. WHO indicates World Health Organization.
aIdentified later retrospectively.
The timing of the COVID-19 outbreak, prior to
China’s annual Lunar New Year holiday, was an important factor as China
considered how to respond to the outbreak. Culturally, this is the largest and
most important holiday of the year. It is the expectation that people return to
their family homes, which is the cause for the several billion person-trips
made by residents and visitors during this time, mostly on crowded planes,
trains, and buses. Knowing this meant each infected person could have numerous
close contacts over a protracted time and across long distances, the government
needed to quickly act. However, it was not only the speed of the government’s
response, but also the magnitude of that response that were influenced by the
impending holiday travel time. Knowing that specific treatment and prevention
options, such as targeted antiviral drugs and vaccines, were not yet available
for COVID-19, China focused on traditional public health outbreak response
tactics—isolation, quarantine, social distancing, and community containment.3-5
Identified case patients with COVID-19 were
immediately isolated in designated wards in existing hospitals, and 2 new
hospitals were rapidly built to isolate and care for the increasing numbers of
cases in Wuhan and Hubei. People who had been in contact with COVID-19 cases were
asked to quarantine themselves at home or were taken to special quarantine
facilities, where they could be monitored for onset of symptoms. Enormous
numbers of large gatherings were canceled, including all Lunar New Year
celebrations, and traffic in Wuhan and in cities across Hubei was restricted
and closely monitored. Virtually all transportation was subsequently restricted
at a national level. All of these measures were instituted to achieve social
distancing. In addition, an estimated 40 million to 60 million residents of
Wuhan and 15 other surrounding cities within Hubei Province were subjected to
community containment measures. Although these types of traditional outbreak
response actions have been successfully used in the past, they have never been executed
on such a large scale.
There have been some questions about whether
these actions are reasonable and proportional responses to the outbreak. Some
have argued that a number of these approaches may infringe on the civil
liberties of citizens, and some of these measures have been referred to as
“draconian.” However, it is not only individual rights that must be considered.
The rights of those who are not infected, but at risk of infection, must be
considered as well. Whether these approaches have been effective (eg, in terms
of reduced infections and deaths averted), and whether these potential benefits
have outweighed the costs (eg, economic losses), will be debated for years.4,5
Next Steps
Importantly, another major goal of China’s
current outbreak response activities is to help “buy time” for science to catch
up before COVID-19 becomes too widespread. China must now focus on adjusting
tactics and strategies as new evidence becomes available.3,6 Much remains to be done and many questions remain
unanswered. China is very grateful for the help it is receiving from the
international scientific, health, and public health communities. The global
society is more interconnected than ever, and emerging pathogens do not respect
geopolitical boundaries. Proactive investment in public health infrastructure
and capacity is crucial to effectively respond to epidemics like COVID-19, and
it is critical to continue to improve international surveillance, cooperation,
coordination, and communication about this major outbreak and to be even better
prepared to respond to future new public health threats.
Corresponding Author: Zunyou Wu, MD, PhD, Chinese Center for
Disease Control and Prevention, 155 Changbai Rd, Beijing 102206, China (wuzy@263.net).
Conflict of Interest Disclosures: None reported.
Funding/Support: This work was supported by the National
Health Commission of the People’s Republic of China (2018ZX10721102).
Role of the Funder/Sponsor: The funder had no role in the
preparation, review, or approval of the manuscript, or the decision to submit
the manuscript for publication.
Disclaimer: The opinions expressed herein reflect the collective views
of the coauthors and do not necessarily represent the official position of the
Chinese Center for Disease Control and Prevention.
Additional Contributions: We thank China CDC Weekly for
its permission to re-create the epidemic curve with modifications.
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