Emerging infectious diseases represent a serious threat for human public health worldwide.[1,2]
The 2019 novel coronavirus (2019-nCoV) caused a pneumonia outbreak, which is spreading
around the country and has affected 32 provinces and regions of China as of January
27, 2020.[3,4] Countries outside China, including Japan, the United States, Thailand,
and South Korea, have also reported cases imported from other countries.[5] With the
joint efforts of Chinese scientists, health workers, and related departments, the
pathogen causing this epidemic was quickly identified as a new type of coronavirus,
10 days after the first official report. After confirming the pathogen, specific detection
methods were rapidly developed, with improvement in etiological diagnosis. As of January
22, 2020, it has been confirmed that the new coronavirus came from wild bats and belonged
to group 2b of the beta coronavirus, which includes severe acute respiratory syndrome-associated
coronavirus (SARS-CoV).[6] Although 2019-nCoV and SARS-CoV belong to the same sub-group
of beta coronaviruses, the similarity at the genome level is only 80%,[7,8] meaning
that the new virus is genetically different from SARS-CoV [Supplementary Figure 1A].
Rapid discovery of the causative agent and development of diagnostic reagents demonstrated
that technology has greatly improved in the 17 years since the SARS outbreak. However,
no effective anti-viral medication or vaccines are available for this new virus, and
many of its aspects remain to be explored. Similar to the SARS outbreak, this outbreak
also occurred during the spring festival, the most important of the Chinese traditional
festivals, when 3 billion people travel throughout the country.[9] This unexpectedly
provides beneficial conditions for the transmission of this highly infectious disease
and correspondingly poses great challenges for the prevention and control of the outbreak.
Although technology has greatly improved since the 2003 SARS outbreak, the basic laws
and characteristics of the occurrence and development of infectious diseases have
not fundamentally changed.[10] Therefore, the epidemic laws and characteristics of
the SARS outbreak and the painful lessons we learned in responding to the epidemic
are of great value currently and in the future. Due to concerns about controlling
the impact of the epidemic and the relatively less developed information exchange
tools of that time, the early epidemics and characteristics of the early SARS cases
were not reported. However, as we had participated in the epidemiological investigations
of early SARS cases in 2003, we had collected important data about the early stages
of the outbreak. Using these valuable data, we analyzed the characteristics of the
early SARS cases and the progression of the outbreak. By comparing the epidemic situations
of the two outbreaks, we found some strikingly similar characteristics and trends,
providing lessons for better responses to the present and future epidemics.
On January 2, 2003, a hospital in Heyuan city, Guangdong Province, reported two strange
cases of severe pneumonia, which were then transferred to a larger hospital for further
treatment. Several days later, seven medical staff members in the department that
treated these patients developed symptoms. Retrospective investigation found that
a hospital in Foshan had treated a similar case on November 25, 2002 [Supplementary
Figure 2A]. This patient developed symptoms on November 16, 2002, and subsequently,
five family members also developed symptoms. This indicated that SARS-CoV emerged
with high human-to-human transmission capability, characterized by familial and medical
staff infections.[11,12] An investigation of family clustering identified 35 clusters
involving 105 patients, in families with two or more family members in Guangzhou.
The largest cluster was derived from a female patient. A total of 91 persons were
infected due to visiting or nursing the female patient, and two of these people died[13]
[Supplementary Figure 2B]. This indicated that the super virus spreader emerged at
the earliest stage of the outbreak, confirming the high infection capability of the
virus.[14,15] Subsequent case investigations also showed that SARS-CoV had the capability
to multiply and continuously undergo human-to-human transmission [Supplementary Figure
2C]; at least four generations of cases were identified from one original patient.
Among the clusters of cases, healthcare workers were common victims.[16] As of April
13, 2003, a total of 48 medical institutions had medical staff with SARS-CoV infection,
and 33 medical institutions in Guangzhou reported a total of 283 cases. The incidence
among medical staff in the respiratory care department of a university affiliated
hospital in Guangzhou was 61.7% (29/47), that is, more than half of the medical staff
were infected while treating their patients.[17]
As for the 2019-nCoV outbreak, the first patient with unexplained pneumonia was identified
on December 12, 2019. On December 31, 2019, 27 cases of viral pneumonia were officially
announced; seven of these patients were in a severe condition.[18] Respiratory infectious
diseases, including influenza, SARS, and Middle East respiratory syndrome, were screened
for and excluded.[19] On January 3, 2020, only 1 week later, a new type of coronavirus
was discovered. The identification of pathogenic nucleic acids was completed on January
10,[20] and on January 12, the World Health Organization officially named the new
coronavirus the “2019 novel coronavirus.” It took less than 10 days from the first
official announcement to the identification of the pathogen. In contrast to that of
SARS-CoV, the discovery of human-to-human transmission of 2019-nCoV came relatively
late. On December 31, 2019, 27 confirmed pneumonia cases were officially reported,
no human-to-human transmission case was identified.[18] On January 19, 2020, a cluster
of cases, including 15 healthcare workers, were confirmed to have been infected via
patients, confirming that 2019-nCoV also has human-to-human transmission capability.[21]
Based on these results, it was concluded that 2019-nCoV also has high human-to-human
transmission capability. It remains unclear whether earlier cases also showed this
capability, and if so, how many victims were not identified. The close contacts of
these unidentified patients might act as new infection sources and could become super-spreaders.
The incidence and development process of the SARS outbreak has valuable implications
for the 2019-nCoV outbreak. After discovering the earliest case identified on November
16, 2002, the incidence remained low until January 2, 2003. The peak of the incidence
was observed between January 3 and February 4, 2003, and the number of cases accounted
for 54.7% of the total cases (Wikipedia). According to the case numbers and the developmental
characteristics, the SARS epidemic can be roughly divided into four stages: stage
1, from November 16, 2002 to January 31, 2003; stage 2, from February 1 to March 2,
2003; stage 3, from March 3 to April 2; and stage 4, after April 4 [Supplementary
Figure 2D]. Coincidentally, the SARS outbreak duration also coincided with the Chinese
spring festival. Each year, the Chinese government launches a 40-day spring festival
transport support system, and during this period, billions of people migrate around
China. In 2003, the spring festival transport period started from January 17 to February
25, 2003 and coincided with the peak incidence [Supplementary Figure 2D, purple box].
The spring festival travel period in 2020 started from January 10 to February 18,
which coincided with the rapid increase in 2019-nCoV cases between January 10 and
22, 2020 [Supplementary Figure 2D, red box]. Both outbreaks happened in the winter,
when the two provinces have similar climate patterns suitable for virus survival and
spread. Temperature and weather are risk factors of natural infectious diseases, and
those in Wuhan and Guangzhou seem to be suitable for disease transmission. Given previous
trends, this is unlikely to be the incidence peak of this new virus outbreak. The
daily counts of 2019-nCoV cases were higher than the daily counts of SARS cases during
its peak in 2003, implying a possibly higher number of cumulative cases.[10] We analyzed
the transportation between different and large cities. High frequency transportation
is mainly distributed among megacities [Supplementary Figure 2E]. The highest ranked
cities include Beijing, Guangzhou, and Shanghai.[22] Wuhan has a population of 10
million and is also a major hub of the spring festival transportation network.[23]
The predicted number of passengers traveling during the 2020 spring festival is 3.11
billion, 1.7 times the total number in 2003 (1.82 billion) [Supplementary Figure 2F].
This large-scale migration has brought favorable conditions for disease spread that
are difficult to control.
Because we are now in the early stage of the outbreak, we must be prepared for subsequent
larger-scale outbreaks and predict the scale of the outbreak. Since 2019-nCoV is highly
similar to SARS-CoV, some important characteristics of SARS-CoV could be used for
this prediction. By combining the reported daily counts of 2019-nCoV cases and data
from the SARS outbreak, we constructed a logistic model and predicted the incidence
of 2019-nCoV over time. During the 2003 SARS outbreak, a total of 8000 cases were
reported.[24] With this data and the present situation, we predict that the cumulative
number of 2019-nCoV cases might be 60,000 to 70,000. Logistic models were fitted to
these data, and the cumulative and daily counts of 2019-nCoV cases were predicted.
As shown in Supplementary Figure 1B and 1C, we also calculated the time needed to
reach the peak of incidence under different scenarios. Setting the upper limit of
cumulative incidence (K) to 50,000, 60,000, or 70,000, the end date of incidences
will be in 56 days (March 6, 2020), 60 days (March 10, 2020), or 62 days (March 12,
2020), respectively.
Using valuable epidemiological data from the SARS outbreak, we systematically evaluated
and compared the characteristics of the 2019-nCoV and SARS-CoV outbreaks. The two
outbreaks share many similarities, and the ongoing 2019-nCoV outbreak situation seems
to be a repetition of the SARS-CoV outbreak situation. Fortunately, the Chinese government
is implementing many efficient measures, including shutting down public transportation
in Wuhan and other cities, reducing population migration, and encouraging personal
protection such as face mask-wearing. With these measures, case numbers could be reduced
significantly. However, due to the lack of awareness regarding the human-to-human
transmission capability of 2019-nCoV in the early stages, there is a possibility that
super-spreaders exist.[25] These super-spreaders may be distributed in different places
and are difficult to track. This represents the most important problem for this outbreak.
Acknowledgements
The authors thank the collaborators who participated in the original investigations
during the 2002 to 2003 SARS outbreak.
Funding
This work was supported by grants from the National Key Research and Development Program
Projects of China (No. 2017YFD0500305), the National Key Program for Infectious Disease
of China (No. 2018ZX10101002-002), the State Key Program of National Natural Science
of China (No. U1808202), Guangdong Province Key Area R & D Plan Project (No. 2018B020241002),
and the Guangdong Provincial Science and Technology Project (No. 2018B020207013).
Conflicts of interest
None.
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