China CDC Weekly

Vital Surveillances

The Epidemiological Characteristics of an Outbreak of 2019 Novel
Coronavirus Diseases (COVID-19) — China, 2020
The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team

Abstract
Background: An outbreak of 2019 novel coronavirus
diseases (COVID-19) in Wuhan, Hubei Province,
China has spread quickly nationwide. Here, we reportresults of a descriptive, exploratory analysis of all cases
diagnosed as of February 11, 2020.
Methods: All COVID-19 cases reported throughFebruary 11, 2020 were extracted from China’s
Infectious Disease Information System. Analyses
included the following: 1) summary of patientcharacteristics; 2) examination of age distributions andsex ratios; 3) calculation of case fatality and mortality
rates; 4) geo-temporal analysis of viral spread; 5)epidemiological curve construction; and 6) subgroup
analysis.
Results: A total of 72,314 patient records—44,672(61.8%) confirmed cases, 16,186 (22.4%) suspectedcases, 10,567 (14.6%) clinically diagnosed cases(Hubei Province only), and 889 asymptomatic cases(1.2%)—contributed data for the analysis. Among
confirmed cases, most were aged 30–79 years (86.6%),
diagnosed in Hubei (74.7%), and considered mild
(80.9%). A total of 1,023 deaths occurred among
confirmed cases for an overall case fatality rate of 2.3%.
The COVID-19 spread outward from Hubei Province
sometime after December 2019, and by February 11,2020, 1,386 counties across all 31 provinces wereaffected. The epidemic curve of onset of symptoms
peaked around January 23–26, then began to decline
leading up to February 11. A total of 1,716 healthworkers have become infected and 5 have died (0.3%).
Conclusions: COVID-19 epidemic has spread very
quickly taking only 30 days to expand from Hubei tothe rest of Mainland China. With many people
returning from a long holiday, China needs to prepare
for the possible rebound of the epidemic.

Introduction
A cluster of pneumonia cases of unknown origin in
Wuhan, China caused concern among health officials
Chinese Center for Disease Control and Prevention

in late December 2019. On December 31, an alert wasissued by the Wuhan Municipal Health Commission,a rapid response team was sent to Wuhan by the
Chinese Center for Disease Control and Prevention(China CDC), and a notification was made to theWorld Health Organization (WHO) (1–4). Likely
potential causes including influenza, avian influenza,
adenovirus, severe acute respiratory syndrome
coronavirus (SARS-CoV), and Middle East respiratory
syndrome coronavirus (MERS-CoV) were ruled out.
Epidemiological investigation implicated Wuhan’s
Huanan Seafood Wholesale Market, which was shut
down and disinfected, and active case finding was
initiated and vigorously pursued (2,4–5).
On January 7, 2020, the causative pathogen was
identified as a novel coronavirus, and genomic
characterization and test method development ensued(2–6). Now named 2019-nCoV, the virus is distinct
from both SARS-CoV and MERS-CoV, yet closely
related (5,7). Early cases suggested that COVID-19(i.e. the new name for disease caused by the novel
coronavirus) may be less severe than SARS and MERS.
However, illness onset among rapidly increasing
numbers of people and mounting evidence of humanto-human transmission suggests that 2019-nCoV ismore contagious than both SARS-CoV and MERSCoV (3,8–11).
On January 20, China’s “National Infectious Diseases
Law” was amended to make 2019-novel coronavirus
diseases (COVID-19) a Class B notifiable disease andits “Frontier Health and Quarantine Law” was amended
to support the COVID-19 outbreak response effort.
Then, on January 23, the Chinese Government began
to limit movement of people in and out of Wuhan,
and two days later, it announced its highest-levelcommitment and mobilized all sectors to respond to
the epidemic and prevent further spread of COVID19. Characterization of the epidemiological features of
COVID-19 is crucial for the development andimplementation of effective control strategies. Here, wereport the results of a descriptive, exploratory analysisof all cases found through February 11, 2020.
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MethodStudy Design
This study was a descriptive, exploratory analysis of
all cases of COVID-19 diagnosed nationwide in China
as of the end of February 11, 2020. As such, it in somerespects uses a cross-sectional study design and hence,
we have used the STROBE Guidelines (www.equatornetwork.org) to aid our thorough reporting of thisobservational study.
A public health emergency was declared, and aformal investigation began on December 31, 2019,supported by city (Wuhan Municipal HealthCommission and Wuhan CDC), provincial (HealthCommission of Hubei Province and Hubei Provincial
CDC), and national (National Health Commission
and China CDC) authorities and resources. This study
was reviewed by the China CDC Institutional Review
Board via a fast-track mechanism. Although individual
informed consent was not required for this study, alldata were handled as a deidentified set to protect
patient privacy and confidentiality.

Data Source
By categorizing COVID-19 as a Class B notifiabledisease, Chinese law required all cases to be
immediately reported to China’s Infectious Disease
Information System. Entry of each case into the system
was performed by local epidemiologists and publichealth workers who investigated and collected
information on possible exposures. All case records
contain national identification numbers, and therefore,
all cases have records in the system and no records are
duplicated. All data contained in all COVID-19 caserecords in the Infectious Disease Information Systemthrough the end of February 11, 2020 were extracted
from the system as a single dataset and were thenstripped of all personal identifying information. No
sampling was done to achieve a predetermined study
size and no eligibility criteria were used—all cases were
included.

Variables
Patient characteristics were collected at baseline,
meaning the time of diagnosis, epidemiologicalinvestigation, and entry into the Infectious Disease
Information System. Patients were categorized ashealth workers for the occupation variable if they had
active employment of any kind in a health facility (i.e.
this category did not just include physicians and114

CCDC Weekly / Vol. 2 / No. 8

nurses). Patients were categorized as having a Wuhanrelated exposure if they had recently resided in orvisited Wuhan or if they had close contact withsomeone who had. The comorbid conditions variable
was determined upon epidemiological investigation by
patient self-reported medical history, which was notindependently verified using medical records for allcases. The severity of symptoms variable wascategorized as mild, severe, or critical. Mild included
non-pneumonia and mild pneumonia cases. Severe wascharacterized by dyspnea, respiratory frequency ≥30/minute, blood oxygen saturation ≤93%, PaO2/FiO2
ratio <300, and/or lung infiltrates >50% within 24–48
hours. Critical cases were those that exhibited
respiratory failure, septic shock, and/or multiple organ
dysfunction/failure.
As some variables of interest (i.e., Wuhan-related
exposure, comorbid condition, and case severity) are
not required fields when creating records in the
Infectious Disease Information System, some records
have missing data for these variables.
For construction of epidemiological curves, date of
onset was defined as the date on which patients selfreported the start of either fever or cough during
epidemiological investigation. Cases were categorized
as confirmed, suspected, clinically diagnosed (Hubei
Province only), or asymptomatic. Confirmed cases
were diagnosed based on positive viral nucleic acid test
results on throat swab samples (some samples were
tested retrospectively). Suspected cases were diagnosed
clinically based on symptoms and exposures. Clinicallydiagnosed cases were suspected cases with lung imaging
features consistent with coronavirus pneumonia.
Asymptomatic cases were diagnosed based on positive
viral nucleic acid test results but without any COVID19 symptoms (e.g., fever, dry cough). The date of
positive viral nucleic acid test result is used as onset
date for asymptomatic cases

Analysis
For confirmed cases, demographic and clinicalcharacteristics were summarized using descriptive
statistics. Age distribution graphs were constructedusing patient age at baseline for confirmed cases
diagnosed in Wuhan, Hubei Province (including
Wuhan), and China (including Hubei Province). Sex
ratio (i.e., male:female [M:F] ratio) was also calculated.
Case fatality rates were calculated as the total numberof deaths (numerator) divided by the total number ofcases (denominator), expressed as a percent. Observed
time was summarized using person-days (PD) andChinese Center for Disease Control and Prevention

China CDC Weekly

mortality was calculated as the number of deaths(numerator) divided by the total observed time(denominator), expressed per 10 PD.
For geo-temporal analysis, the county-level locationof each case at time of diagnosis was used to build
color-coded maps of China to indicate the numbers ofcases in each province on December 31, 2019; January
10, 2020; January 31, 2020; and February 11, 2020.
This analysis was performed using ArcGIS Desktop
software (version 10.6; Esri; Redlands, California,
USA).
The epidemiological curve for all cases wasconstructed by plotting the number of cases (y-axis)
versus self-reported date of symptom onset (x-axis).
Date of symptom onset for confirmed, suspected,
clinically diagnosed, and asymptomatic cases werestacked to show total cases over time. The
epidemiological curve for confirmed cases was also
overlaid with the number of cases versus date ofdiagnosis to show the delay between onset ofsymptoms and diagnosis of disease.
Two subgroups were also analyzed separately using
epidemiological curves: confirmed cases diagnosed
outside of Hubei Province (with and without Wuhan-related exposure) and all cases diagnosed among healthworkers (confirmed, suspected, clinically diagnosed,
and asymptomatic).

Results
Patients
A total of 72,314 unique records were extracted anddata from all records were included in the analysis.
Thus, all 72,314 individuals diagnosed with COVID19 as of February 11, 2020, were included in theanalysis. Among them, 44,672 cases (61.8%) wereconfirmed, 16,186 cases (22.4%) were suspected,
10,567 cases (14.6%) were clinically diagnosed, and889 cases (1.2%) were asymptomatic.
Baseline characteristics of confirmed cases(n=44,672) are presented in Table 1. A majority wereaged 30–69 years (77.8%), male (51.4%), farmers orlaborers (22.0%), and diagnosed in Hubei Province(74.7%). Most patients reported Wuhan-related
exposures (85.8%) and were classified as mild cases(80.9%).

TABLE 1. Patients, deaths, and case fatality rates, as well as observed time and mortality for n=44,672 confirmed COVID-19
cases in Mainland China as of February 11, 2020.
Baseline characteristics
OverallConfirmed cases,
N (%)

Deaths,N (%)

Case fatality
rate, %

Observed time,PD

Mortality,
per 10 PD

44,672

1,023

2.3

661,609

0.015

Age, years
0–9

416 (0.9)

−

−

4,383

−

10–19

549 (1.2)

1 (0.1)

0.2

6,625

0.002

20–29

3,619 (8.1)

7 (0.7)0.2

53,953

0.001

30–39

7,600 (17.0)

18 (1.8)

0.2

114,550

0.002

40–49

8,571 (19.2)

38 (3.7)

0.4

128,448

0.003

50–59

10,008 (22.4)

130 (12.7)

1.3

151,059

0.009

60–69

8,583 (19.2)

309 (30.2)

3.6

128,088

0.024

70–79

3,918 (8.8)

312 (30.5)

8.0

55,8320.056≥80

1,408 (3.2)

208 (20.3)

14.8

18,671

0.111

Male

22,981 (51.4)

653 (63.8)

2.8

342,0630.019

Female21,691 (48.6)

370 (36.2)

1.7

319,546

0.012

Service industry

3,449 (7.7)

23 (2.2)

0.7

54,4840.004

Farmer/laborer

9,811 (22.0)

139 (13.6)

1.4

137,992

0.010

Health worker

1,716 (3.8)

5 (0.5)

0.3

28,0690.002

Retiree

9,193 (20.6)

472 (46.1)

5.1

137,118

0.034

Other/none

20,503 (45.9)384 (37.5)

1.9

303,946

0.013

Sex

Occupation

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TABLE 1. (continued)
Confirmed cases,
N (%)

Deaths,N (%)

Case fatality
rate, %

Observed time,PD

Mortality,
per 10 PD

Hubei

33,367 (74.7)

979 (95.7)

2.9

496,523

0.020

Other

11,305 (25.3)

44 (4.3)

0.4

165,086

0.003

Yes

31,974 (85.8)

853 (92.8)

2.7

486,6120.018

No5,295 (14.2)

66 (7.2)

1.2

71,201

0.009

7,403

104

2.8

103,7960.010

Hypertension

2,683 (12.8)

161 (39.7)

6.0

42,6030.038

Diabetes

1,102 (5.3)

80 (19.7)

7.3

17,9400.045

Cardiovascular disease

873 (4.2)

92 (22.7)

10.5

13,5330.068

Chronic respiratory disease

511 (2.4)

32 (7.9)

6.3

8,083

0.040

Cancer (any)Baseline characteristics
Province

Wuhan-related exposure*

Missing
Comorbid condition†

107 (0.5)

6 (1.5)

5.6

1,690

0.036

None

15,536 (74.0)

133 (32.8)

0.9

242,948

0.005

Missing

23,690 (53.0)

617 (60.3)

2.6

331,843

0.019

Mild

36,160 (80.9)

−

−

−

−

Severe6,168 (13.8)

−

−

−

−

Critical

2,087 (4.7)

1,023 (100)49.0

31,4560.325

Missing

257 (0.6)

−

−

−

−

Case severity§

Period (by date of onset)
Before Dec 31, 2019104 (0.2)

15 (1.5)

14.4

5,142

0.029

Jan 1–10, 2020

653 (1.5)

102 (10.0)

15.6

21,6870.047

Jan 11–20, 2020

5,417 (12.1)

310 (30.3)

5.7

130,972

0.024

Jan 21–31, 2020

26,468 (59.2)

494 (48.3)

1.9

416,009

0.012

After Feb 1, 2020

12,030 (26.9)
102 (10.0)
0.8
87,7990.012
Abreviation: PD, person-days. -, not applicable.
* The Wuhan-related exposure variable, only includes a total of 37,269 patients and 919 deaths and these values were used to calculate
percentages in the confirmed cases and deaths columns.
†
The comorbid condition variable, only includes a total of 20,812 patients and 504 deaths and these values were used to calculate
percentages in the confirmed cases and deaths columns.
§
The case severity variable, only includes a total of 44,415 patients and 1,023 deaths and these values were used to calculate percentages
in the confirmed cases and deaths columns.

Deaths, Case Fatality Rates, and Mortality
As shown in Table 1, a total of 1,023 deaths haveoccurred among 44,672 confirmed cases for an overallcase fatality rate of 2.3%. Additionally, these 1,023
deaths occurred during 661,609 PD of observed time,
for a mortality rate of 0.015/10 PD.
The ≥80 age group had the highest case fatality rateof all age groups at 14.8%. Case fatality rate for males
was 2.8% and for females was 1.7%. By occupation,
patients who reported being retirees had the highest
case fatality rate at 5.1%, and patients in Hubei
Province had a >7-fold higher case fatality rate at 2.9%
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CCDC Weekly / Vol. 2 / No. 8

compared to patients in other provinces (0.4%). Whilepatients who reported no comorbid conditions had acase fatality rate of 0.9%, patients with comorbid
conditions had much higher rates—10.5% for thosewith cardiovascular disease, 7.3% for diabetes, 6.3%
for chronic respiratory disease, 6.0% for hypertension,and 5.6% for cancer. Case fatality rate was also very
high for cases categorized as critical at 49.0%.

Age Distribution and Sex Ratio
The age distribution of cases in Wuhan only, in
Hubei Province overall, and in China overall are
Chinese Center for Disease Control and Prevention

China CDC Weekly

presented in Figure 1. The proportion of confirmed
cases 30–79 years of age at baseline (i.e., date ofdiagnosis) was 89.8% for cases in Wuhan city versus
88.6% in Hubei overall (which includes Wuhan) and
86.6% in China overall (which includes Hubei
Province and all 30 other provincial-level
administrative divisions, or PLADs). The male-tofemale ratio was 0.99:1 in Wuhan, 1.04:1 in Hubei,
and 1.06:1 in China overall.

and Hubei Province accounted for 88.5% (Figure 2B);
13.8% had onset of illness during January 11–20,
2020, distributed in 627 counties of 30 PLADs andHubei Province accounted for 77.6% (Figure 2C);
73.1% had onset of illness during January 21–31,
2020, distributed in 1310 counties of 31 PLADs andHubei Province accounted for 74.7% (Figure 2D).

Epidemiological Curve
Figure 3A shows the COVID-19 epidemic curvewith number of cases plotted by date of patient onsetof symptoms from December 8, 2019 to February 11,2020. Confirmed, suspected, clinically diagnosed, andasymptomatic cases are stacked to show total dailycases by date of symptom onset. The inset shows thatin December 2019 only 0–22 cases/day began toexperience symptoms. The peak onset of symptoms for
all cases overall occurred on February 1, 2020. Since
then, onset of illness has declined.
Figure 3B shows the same COVID-19 epidemic
curve for confirmed cases only with number of cases
plotted by date of patients’ onset of symptoms from
December 8, 2019 to February 11, 2020. These data
are overlaid with confirmed cases plotted by date ofdiagnosis to show the lag between the time patients fall
ill and the time they actually are diagnosed and arereported to the Infectious Disease Information System.
Although for confirmed cases onset of illness peakedaround January 23–27, diagnosis of infection by
nucleic acid testing of throat swabs did not peak until
February 4.

Geo-Temporal Findings
On January 19, 2020, National Health Commissionof the People’s Republic of China confirmed that
Guangdong Provincial CDC reported first imported
cases of COVID-19, via the Chinese Infectious
Diseases Reporting System. This was the first time
COVID-19 had been reported outside of Hubei
Province via the System. As of January 22, 2020, a
total of 301 confirmed COVID-19 cases were reported
from 83 counties in 23 provinces. On January 30,
2020, Xizang Autonomous Region (Tibet) reported its
first confirmed COVID-19 case coming from Hubei
Province. Thus, COVID-19 cases have been reported
from all 31 PLADs (Figure 2).
As of February 11, 2020, a total 44,672 confirmed
cases were reported from 1,386 counties of 31
provinces, autonomous regions, and municipalities andHubei Province accounted for 74.7% (Figure 2E).
Among them, 0.2% of cases had onset of illness before
December 31, 2019 and all were from Hubei Province(Figure 2A); 1.7% had onset of illness during January
1–10, 2020, distributed in 113 counties of 22 PLADsA
0–9 0.4%

Wuhan

10–19 0.4%
20–29
Age, years

60–69

22.4%

21.4%
10.1%

89.8% 30–79

4.5%

19.2%
23.4%

26.5%
12.6%

17.0%

18.3%
22.0%

70–79

8.1%
15.4%

15.6%

50–59

China

1.2%

6.6%
13.1%

40–49

C
0.9%

Hubei

0.7%

4.5%

30–39

80–89

B
0.4%

3.3%

19.2%
8.8%

88.6% 30–79

86.6% 30–79

2.9%

90–99+ 0.5%

0.3%

0.3%

M:F Ratio 0.99:1

1.04:1

1.06:1FIGURE 1. Age distribution and sex ratio of all confirmed COVID-19 cases in China through February 11, 2020. (A) patientsdiagnosed in the city of Wuhan only; (B) patients diagnosed in Hubei Province, which includes Wuhan as its capital city; and(C) patients diagnosed in China overall, including Hubei Province and all 30 other provincial-level administrative divisions(PLADs). Dashed red line highlights the proportion of patients in the 30–79 years age range. Sex ratio (i.e. male-to-female[M:F] ratio) is shown below each graph.

Chinese Center for Disease Control and Prevention

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China CDC WeeklyA

December 31, 201914 counties in 1 province

January 10, 2020

January 20, 2020

C 627 counties in 30 provinces D

B 113 counties in 20 provinces
Heilongjiang

Heilongjiang

Jilin
InnerMonglia
Liaoning

Xinjiang

Ningxia

Ningxia

Tibet

Hubei

Tibet

Guizhou
YunnanGuizhou
YunnanGuangxi Guangdong
Hong Kong

No. of confirmed cases
≤50
≤100
≤300
≤500
≤1,000>1,000No dataWuhan

Sichuan Chongqing

Zhejiang

Hunan Jiangxi
FujianHainanTibet

Ningxia

Shanxi Henan

Jiangsu
Anhui Shanghai

Tibet

Hubei
Sichuan Chongqing

Zhejiang

Hunan Jiangxi
FujianGuangxi Guangdong
Hong Kong

No. of confirmed cases
≤50
≤100
≤300
≤500
≤1,000>1,000No dataBeijing
Tianjin
Hebei
ShanxiShandong

Gansu

Qinghai
Shanxi Henan

Jiangsu
Anhui Shanghai

Hubei

Hubei
Sichuan Chongqing

Hubei

Ningxia
Qinghai

Shanxi Henan

Jiangsu
Anhui Shanghai

Jilin
InnerMonglia
Liaoning

Xinjiang

Beijing
Tianjin
Hebei
ShanxiShandong

Gansu

Qinghai
Shanxi Henan

Heilongjiang

Jilin
InnerMonglia
Liaoning

Xinjiang

Beijing
Tianjin
Hebei
ShanxiShandong

Gansu

QinghaiFebruary 11, 2020

E 1,386 counties in 31 provinces

Heilongjiang

Jilin
InnerMonglia
Liaoning

Xinjiang

Beijing
Tianjin
Hebei
ShanxiShandong

Gansu

January 31, 2020
1,310 counties in 31 provinces

Guizhou
TaiwanYunnanHainanGuangxi Guangdong
Hong Kong

No. of confirmed cases
≤50
≤100
≤300
≤500
≤1,000>1,000No data

Jiangsu
Anhui Shanghai

Hubei

Zhejiang

Sichuan Chongqing

Hunan Jiangxi
FujianGuizhou
TaiwanYunnanHainanZhejiang

Hunan Jiangxi
FujianGuangxi Guangdong
Hong Kong

No. of confirmed cases
≤50
≤100
≤300
≤500
≤1,000>1,000No data

TaiwanHainanFIGURE 2. Geo-temporal spread of COVID-19 in China through February 11, 2020. (A) a total of 14 county-level
administrative areas (hereafter counties) in Hubei Province only (inset) had reported cases as of December 31, 2019; (B) by
January 10, 2020, 113 counties in 20 PLADs had reported cases with the highest prevalence still in Hubei Province; (C) ninedays later, on January 20, 627 counties in 30 PLADs had reported cases and PLADs neighboring Hubei Province observed
increasing prevalence; (D) by the end of January 31, 1,310 counties across all 31 PLADs were affected and prevalence inthe central, south, and south-central regions had risen dramatically; (E) by the end of February 11, 1,386 counties
nationwide were affected and prevalence in the south-central PLADs had risen to the level of Hubei.
All cases (n=72,314)
Confirmed

Number of cases

Suspected

Clinically diagnosed

Asymptomatic

24
16
8

1/17

1/19

1/21

1/23

1/25

1/27

1/29

1/31

2/2

2/4

2/6

2/8

2/10

1/19

1/21

1/23

1/25

1/27

1/29

1/31

2/2

2/4

2/6

2/8

2/10

1/15

1/17

1/13

1/9

1/11

1/7

1/5

1/3

1/1

12/30

12/28

12/26

12/24

12/22

12/20

12/18

12/16

12/14

12/12

12/8

0

12/10

A 5,500
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
0

Date of symptom onset
B 4,000
3,500

Confirmed cases only (n=44,672)
By date of onset
By date of diagnosis

Number of cases

3,000
2,500
15

2,000

10

1,500

5
1,000

0

1/15

1/13

1/11

1/9

1/7

1/5

1/3

1/1

12/30

12/28

12/26

12/24

12/22

12/20

12/18

12/16

12/14

12/12

12/8

0

12/10

500

Date

FIGURE 3. Epidemiological curves of COVID-19 in China through February 11, 2020. (A) the epidemiological curve shows
the progression of illness in the outbreak over time from December 8, 2019 to February 11, 2020. A total of 72,314 cases
are shown and confirmed cases (blue) are compared to suspected cases (green), clinically diagnosed cases (yellow), andasymptomatic cases (red). The inset shows a zoomed-in view of all days in December, when total daily count remained
below 24 cases; (B) the epidemiological curve shows the progression of illness in the outbreak over time from December 8,
2019 to February 11, 2020 for confirmed cases only (blue). The number of cases diagnosed each day is also shown for
confirmed cases only (orange). The inset shows a zoomed-in view of all days in December, when total daily count remained
below 15 cases.

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China CDC Weekly

infected individual from Wuhan. Peak timing of onsetof symptoms among health worker cases occurred on
February 1. In the 422 medical facilities serving
COVID-19 patients, a total of 3,019 health workers
have been infected (1,716 confirmed cases), and 5 havedied.
Confirmed cases, case severity, and case fatality rates
among health workers in different areas of China anddifferent time periods are presented in Table 2. A totalof 1,080 confirmed cases among health workers havebeen found in Wuhan, accounting for 64.0% of

Subgroup Findings
Figure 4 shows the COVID-19 epidemic curve with
the number of cases plotted by date of onset ofsymptoms from December 18, 2019 to February 11,2020 for two subgroups—confirmed cases foundoutside of Hubei Province (Figure 4A) and all cases
among health workers nationwide (Figure 4B). Peaktiming of onset of symptoms among cases outside of
Hubei Province occurred on January 27. Most of thesecases (85.8%) reported having recently resided in orvisited Wuhan or having had close contact with an
A 600

Confirmed cases outside hubei (n=8,656)
Wuhan-related exposure

Number of cases

500

Wuhan-unrelated exposure

400
300
200

1/21

1/23

1/25

1/27

1/29

1/31

2/2

2/4

2/6

2/8

2/10

1/23

1/25

1/27

1/29

1/31

2/2

2/4

2/6

2/8

2/10

1/19

1/21

1/17

1/15

1/13

1/9

1/11

1/7

1/5

1/3

1/1

12/30

12/28

12/26

12/24

12/22

12/20

0

12/18

100

Date of symptom onset
B 200

All cases among health workers (n=3,019)
Confirmed
Suspected

Number of cases

150

Clinically diagnosed
Asymptomatic
100

1/19

1/17

1/15

1/13

1/11

1/9

1/7

1/5

1/3

1/1

12/30

12/28

12/26

12/24

12/22

12/20

0

12/18

50

Date of symptom onset

FIGURE 4. Subgroup epidemiological curves of COVID-19 in China through February 11, 2020. (A) subgroup analysis ofconfirmed cases discovered outside of Hubei Province only. The epidemiological curve shows the progression of illness inthe outbreak over time from the onset of symptoms of the first case outside Hubei Province on December 18, 2019 throughthe end of February 11, 2020. Total confirmed cases outside Hubei Province, and Wuhan-related exposure (dark purple)
versus Wuhan-unrelated exposure (light purple), are shown; (B) subgroup analysis of all cases among health workers only.
The epidemiological curve shows the progression of illness in the outbreak over time from the onset of symptoms of the first
health worker case on December 27, 2019 through the end of February 11, 2020. Total cases among health workers andconfirmed (blue) versus suspected (green), clinically diagnosed (yellow), and asymptomatic (red) cases are shown.

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national total. An additional 394 health worker cases(23.3%) were found in Hubei Province (excluding
Wuhan), and 214 cases (12.7%) were found in theother 30 PLADs. The proportion of health worker
cases that were severe or critical was 17.7% in Wuhan,
10.4% in Hubei Province, 7.0% in the remaining 30
PLADs, and 14.6% overall. The proportion of healthworker cases in Wuhan classified as severe or criticaldeclined from 38.9% in early January to 12.7% inearly February. In China overall, the severe or criticalcases among health workers also declined—from
45.0% in early January to 8.7% in early February.

Discussion
A main finding of this characterization andexploratory analysis of the first 72,314 cases of
COVID-19 found in China in the 40 days between
first recognition of the outbreak of pneumonia withunknown etiology on December 31, 2019 to the endof the study period on February 11, 2020 is that thisnovel coronavirus is highly contagious. It has spreadextremely rapidly from a single city to the entire
country within only about 30 days. Moreover, it has
achieved such far-reaching effects even in the face of
extreme response measures including the complete
shutdown and isolation of whole cities, cancellation ofChinese New Year celebrations, prohibition of
attendance at school and work, massive mobilization ofhealth and public health personnel as well as military
medical units, and rapid construction of entire
hospitals.
In light of this rapid spread, it is fortunate that
COVID-19 has been mild for 81% of patients and has
a very low overall case fatality rate of 2.3%. Among the1,023 deaths, a majority have been ≥60 years of age
and/or have had pre-existing, comorbid conditions
such as hypertension, cardiovascular disease, anddiabetes. Moreover, the case fatality rate isunsurprisingly highest among critical cases at 49%, andno deaths have occurred among those with mild oreven severe symptoms (Table 1).
A major contribution of our study is a firstdescription of the COVID-19 epidemic curves. We
interpret the overall curve (Figure 3A) as having amixed outbreak pattern—the data appear to indicate acontinuous common source pattern of spread in
December and then from early January throughFebruary 11, 2020, the data appear to have a
propagated source pattern. This mixed outbreak timetrend is consistent with the working theory thatperhaps several zoonotic events occurred at Huanan
Seafood Wholesale Market in Wuhan allowed 2019nCoV to be transmitted from a still-unknown animal
into humans and, due to its high mutation andrecombination rates, it adapted to become capable ofand then increasingly efficient at human-to-humantransmission (3,8).
The early days of the outbreak have been
reminiscent of SARS and MERS, and indeed, thediscovery that the causative agent was a closely-related,never-before-described coronavirus predicted potential
for nosocomial transmission and so-called “superspreader” events (8). Unfortunately, 2019-nCoV did
indeed infect health workers in China via nosocomialtransmission. Here we offer a first description of the
1,716 confirmed cases among health workers. Overall,they also display a likely mixed outbreak
pattern—perhaps the data are characterized by a point
source curve beginning in late December 2019, which

TABLE 2. Confirmed cases, case severity, and case fatality rates among health workers in different areas of China by time
period.
Wuhan
Hubei (outside Wuhan)
China (outside Hubei)
China (overall)
PeriodConfirmed Severe +Confirmed Severe +Confirmed Severe +Confirmed Severe +Deaths, N
Deaths, N
Deaths, N
Deaths, N(by date of onset)
critical,critical,critical,critical,cases,
cases,
cases,
cases,(CFR*, %)(CFR*, %)(CFR*, %)(CFR*, %)
N (%)
N (%)
N (%)
N (%)
N
N
N
N
Before Dec 31, 2019

0

0

0

0

0

0

0

0

0

0

0

0

Jan 1–10, 202018

7 (38.9)

1 (5.6)1

1 (100)01

1 (100)020

9 (45.0)

1 (5.0)

Jan 11–20, 2020233

52 (22.3)

1 (0.4)48

8 (16.7)

029

1 (3.4)0310

61 (19.7)

1 (0.3)

Jan 21–31, 2020

656

110 (16.8)

0250

29 (11.6)

2 (0.8)130

10 (7.7)01,036

149 (14.4)

2 (0.2)After Feb 1, 2020

173

22 (12.7)

1 (0.6)95

3 (3.2)054

3 (5.6)0322

28 (8.7)

1 (0.3)1,080

191 (17.7)

3 (0.3)394

41 (10.4)

2 (0.5)214

15 (7.0)01,688247 (14.6)

5 (0.3)

Total

Abreviation: CFR, case-fatality rate.
* CFR presented here was calculated as number of deaths (numerator) divided by total number of confirmed cases in the row(denominator), expressed as a percent.

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was eclipsed by a higher magnitude continuous source
curve beginning on January 20, 2020. To date, there isno evidence of a super-spreader event occurring in anyof the Chinese health facilities serving COVID-19
patients. However, we do not know whether this is dueto the nature of the virus itself or whether these events
have been successfully prevented.
It is these authors’ sincere hope and intent that thisnew analysis, on what has become a “public healthemergency of international concern,” (12) helps toinform health and public health workers preparing foror perhaps already experiencing COVID-19 in their
populations. This study provides important insight
into several crucial open questions on this epidemic
and how to design strategies to effectively control it(3). For instance, the downward trend in the overall
epidemic curve suggests that perhaps isolation of wholecities, broadcast of critical information (e.g.,
promoting hand washing, mask wearing, and careseeking) with high frequency through multiple
channels, and mobilization of a multi-sector rapid
response teams is helping to curb the epidemic.
China’s response is certainly an echo of lessons
learned during SARS and is a tribute to the work
China and other low- and middle-income countries
have been doing, with the much-needed help ofinternational partners, over the past few decades tobuild infectious disease surveillance systems and publichealth infrastructure capable of catching outbreaks
early and responding swiftly using evidence-based bestpractices. The 2019-nCoV and other coronaviruses
may continue to adapt over time to become morevirulent (3), and zoonosis is not going to stop. We
must remain vigilant, hone our skills, fund our
defenses, and practice our responses, and we must help
our neighbors to do the same.
The very large number of cases included in ourstudy was a major strength. Nevertheless, our study did
have some important limitations. Firstly, a large
proportion of cases included in our analysis (37%)
were not confirmed by nucleic acid testing since thisprocess is slow, labor intensive, and requires specialized
equipment and skilled technicians. Yet all 72,314 cases
were at least diagnosed clinically and investigated bytrained epidemiologists. Secondly, some records did
have missing data for a few important variables ofinterest—Wuhan-related
exposure,
comorbid
conditions, and case severity—which limits our ability
to draw conclusions from the data.
In conclusion, the present descriptive, exploratory
Chinese Center for Disease Control and Prevention

analysis of the first 72,314 cases of COVID-19
reported through February 11, 2020 offers important
new information to the international community on
the epidemic in China. In particular, this analysis
chronicles the extremely rapid spread of the novel
coronavirus despite extreme efforts to contain it.
However, important questions remain including
identification of the animal reservoir, determination of
infectiousness period, identification of transmission
routes, and effective treatment and prevention methods
including further test development, drug development,
and vaccine development (3–4,8–9). As aninternational community, we must all be responsible
partners in surveillance, communication, response,
research, and implementation of evidence-based publichealth and clinical practice. The massive vigorous
actions taken by the Chinese government have slowed
down the epidemic in China and curbed spread to therest of the world. Although the epidemic appears to be
in decline in the lead up to February 11, 2020, we may
yet face more challenges. Huge numbers of people willsoon be returning to work and school after theextended New Year holiday. We need to prepare for a
possible rebound of the COVID-19 epidemic in the
coming weeks and months.

Acknowledgements
This work was supported by National Science andTechnology Foundation of China (2018ZX10201002008-002), and by National Nature Science Foundationof China (NSFC, 71934002). The funder had no rolein the design and conduct of the study; collection,
management, analysis, and interpretation of the data;preparation, review, or approval of the manuscript; anddecision to submit the manuscript for publication.
The team thanks all local health workers for theircontributions in providing testing, treatment, and care
to COVID-19 patients in China.
Disclaimer: The opinions expressed herein reflect
the collective views of the co-authors and do notnecessarily represent the official position of the
National Center for AIDS/STD Control andPrevention of the Chinese Center for Disease Control
and Prevention.
In order to share the results of epidemiologicalcharacteristics of COVID-19 domestically andinternationally, the Chinese Versionis jointly publishedon the Chinese Journal of Epidemiology.
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Author Group & Contributions: The Novel
Coronavirus Pneumonia Emergency Response
Epidemiology Team includes Zijian Feng, Qun Li,
Yanping Zhang#, Zunyou Wu, Xiaoping Dong, Huilai
Ma, Dapeng Yin, Ke Lyu, Dayan Wang, Lei Zhou,
Ruiqi Ren, Chao Li, Yali Wang, Dan Ni, Jing Zhao,
Bin Li, Rui Wang, Yan Niu, Xiaohua Wang, Lijie
Zhang, Jingfang Sun, Boxi Liu, Zhiqiang Deng,
Zhitao Ma, Yang Yang, Hui Liu, Ge Shao, Huan Li,
Yuan Liu, Hangjie Zhang, Shuquan Qu, Wei Lou,Dou Shan, Yuehua Hu, Lei Hou, Zhenping Zhao,
Jiangmei Liu, Hongyuan Wang, Yuanjie Pang, Yuting
Han, Qiuyue Ma, Yujia Ma, Shi Chen, Wei Li,
Routong Yang, Zhewu Li, Yingnan Guo, Xinran Liu,
Bahabaike Jiangtulu, Zhaoxue Yin, Juan Xu, Shuo
Wang, Lin Xiao, Tao Xu, Limin Wang, Xiao Qi,
Guoqing Shi, Wenxiao Tu, Xiaomin Shi, Xuemei Su,
Zhongjie Li, Huiming Luo, Jiaqi Ma, Jennifer M.
McGoogan. All Team members jointly conceptualized
the study, analyzed and interpreted the data, wrote andrevised the manuscript, and decided to submit for
publication.
#

Corresponding author: Yanping Zhang, zhangyp@chinacdc.cn.

Submitted: February 14, 2020; Accepted: February 14, 2020

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Chinese Center for Disease Control and Prevention