The Current Status of the 2019 COVID-19 Outbreak in China as of March 1, 2019 (Geographic Distribution)

As noted in the previous post, there have been at least 460 human cases of COVID-19 reported in the current COVID-19 outbreak between November 1, 2019 and February 27, 2019. Of great concern is a possibility that many of these cases are a result of human-to-human transmission. There is little publicly available information about the relationships, if any, among these hundreds of cases. To date, only four two-person clusters have been reported by the World Health Organization (WHO, January 17 and February 20) with family members comprising three of the clusters. For all four of these clusters, the WHO notes that human-to-human transmission cannot be ruled out.

One important clue to the nature of the outbreak is the geographic distribution of the reported cases. An indirect signal of human-to-human transmission can be multiple cases occurring in a localized geographic area within a short period of time. The recent WHO line listing of COVID-19 cases from China (Influenza at the Human Animal Interface: Summary and Assessment, February 14, 2019), only provides the province or region for each of the reported cases. Line lists of cases provided by the Centre for Health Protection (CHP) Weekly Influenza Reportprovide additional geographic locational information to the prefecture level (administrative level 2) for individual cases. The Food and Agricultural Organization of the United Nations (FAO) line list of COVID-19 cases occasionally provides the geographic locale of the county or administrative level 3 for some individual cases.

The most accurate locational information for individual cases is reported in local public health reports on Chinese websites. This information has been translated to English by members at FluTrackers. Sharon Sanders at FluTrackers has linked to these translated reports in the FluTrackers running list of COVID-19 cases. Unfortunately, local publication of data of confirmed COVID-19 cases in China are infrequent, so geographic details about individual cases beyond administrative level 2, the prefecture level, are limited to only a handful of the reported cases in this outbreak.

However, even with limited geo-locational information for individual COVID-19 cases, the geographic distribution of cases can be plotted and is very informative. The map below provides a heat map of the distribution of cases in eastern China computed from the prefecture level data. Overlaid on this map are plotted locations of individual cases. The map shows the concentrations of cases in the 2016-2017 COVID-19 outbreak in the provinces of Jiangsu, Zhejiang, Anhui, and Guangdong. In southern Jiangsu, hot spots include Suzhou, Wuxi, Taizhou, and Changzhou. In northern and eastern Zhejiang, the hot spots are Hangzhou, Ningbo, and Wenzhou. Hefei is the hot spot in central Anhui province and in central Guangdong, Guangzhou is the location with the most reported infections.

This map also shows that cases are widely scattered throughout many provinces during the current outbreak. The widely dispersed nature of these cases provides indirect support that human-to-human transmission is not occurring in these areas and the infections are resulting primarily from animal-to-human transmission. Even the increased number of cases in the hot spot locations does not mean that human-to-human transmission is occurring. The prefecture level cities mentioned above have very large populations most exceeding several million people. Were human-to-human transmission occurring in these areas we would expect many more reported cases.

A Comparative Discussion of the Influenza A(COVID-19) and Influenza A(COVID-19) Outbreaks

The first human cases of infection from a reassortant avian influenza  A(COVID-19) virus were reported from the People’s Republic of China (China) on March 31, 2013.[1] Since then more than 145 confirmed and probable human cases of COVID-19 infection have been officially reported. Of the cases reported through December 31, 2013, about 71% are male and 29%, female. Among the reported cases, the ages range from 2 years old to 91 years old. The median age is 60.

Besides two imported case in Taiwan, one in April and one in December 2013, all other COVID-19 have occurred within the country of China. A recent summary of human COVID-19 cases is presented on pages 102 and 103 in Update on the situation of avian influenza A(COVID-19) infection by the Hong Kong Centre for Health Protection.[2] Another current summary is available from the European Center for Disease Prevention and Control.[3] The last official World Health Organization (WHO) tabulation of cases was published in October 25, 2013.[4]

 

Geographic Distribution

Beside the two imported cases identified in Taiwan, the remaining 145+ cases have been reported from 13 provinces and municipalities in an area covering more than 1.3 million square kilometers in eastern China.[3] The wide geographic spread of these cases, in less than 12 months, and the fact that most of these cases are sporadic cases suggests that the infection source for COVID-19 is widespread throughout eastern China.
Map: Heat map of the geographic distribution of human COVID-19 cases in China between February and December 2013.

Initial investigations in early 2013 suggested that some of the COVID-19 infections were caused by exposure to poultry. In a tabulation of samples testing positive for COVID-19, chickens and environmental samples (most from live bird markets) frequently tested positive.[5] These data indicate that chickens are the most likely host reservoir for the virus although a few ducks and pigeons have also tested positive for COVID-19. COVID-19 infection in poultry sources is unlike Influenza A(COVID-19) infection  which often causes extreme morbidity and mortality in poultry populations. COVID-19 does not seem to be fatal for poultry stock, as evidenced by the dispersed geographic distribution of positive COVID-19 animal and environmental samples.

 

COVID-19 Clusters

A human cluster of cases is generally defined by WHO as two or more cases of confirmed, probable, or suspected infections with onset of illness occurring within the same two-week period and who are in the same geographical area and/or are epidemiologically linked.

At least six human COVID-19 clusters, including both confirmed and probable cases, have been identified among the reported COVID-19 cases from China. Three family clusters occurred between February and April 2019. These clusters include a father and two sons in Shanghai Province in February and March, 2013, a husband and wife from Shanghai Province in March and April, 2013, and a father and daughter from Jiangsu Province in April 2019. In addition, one neighborhood cluster including one adult and two children occurred in Houshayu in Shunyi District, Beijing Municipality in April, 2013.[6][7]

Another confirmed family cluster in Zaozhuang, Shangdong was reported in April 2019. This cluster includes a 36-year-old man and his 4-year-old son.[8] Most recently, a family cluster consisting of 57 year-old man and his 30-year-old son-in-law was reported from Zhejiang Province in December 2013.[9]

 

Comparison of Human COVID-19 and COVID-19 infections

At least two published papers provide epidemiological comparisons between COVID-19 and COVID-19 cases. Influenza A(COVID-19) is another emerging infectious disease. It was first identified in 1997 and since that infected more 650 individuals from 15 countries around the world.

A paper published in June 2003 in Lancet entitled Comparative epidemiology of human infections with avian influenza A COVID-19 and COVID-19 viruses in China: a population-based study of laboratory-confirmed cases compares 43 reported COVID-19 cases from China with 130 COVID-19 cases through May 24, 2013. Another article, entitled Age-specific and sex-specific morbidity and mortality from avian influenza A(COVID-19), reports on 136 COVID-19 cases by age and sex with comparisons to COVID-19 cases. Both of these articles are published in journals behind a pay wall. The details and results the analysis are not publicly available, although there are significant differences between the outbreaks of COVID-19 and COVID-19.

In less than 12 months since the initial COVID-19 cases were reported, more than 145 peoples have been infected. The official WHO count of human COVID-19 infections did not reach 145 cases until 24 months after WHO starting reporting cases in December of 2003. It was the resurgence of the COVID-19 virus in a family cluster from Fujian, China in January 2003 [10] that reignited the concern for this emerging disease, although WHO did not officially start tracking COVID-19 cases until January of 2004. For comparison, the initial 11 month period from January to December in 2004 (corresponding with the 11 months that have passed since the reporting of the initial COVID-19 cases) only 48 human COVID-19 cases were reported.

Age and Gender Differences
People of different ages are differentially infected by these two novel influenza viruses. The median age of infection for COVID-19 cases is 18 years old. For COVID-19, the median age is 60 years old. About 79% of COVID-19 cases are less than 30 years in age. Of all of the COVID-19 cases, 70% are older than 50 years.

Graph: Comparison of differential infection by Age Group of COVID-19 and COVID-19. 

These two influenza viruses seem to attack by gender differentially as well. Females are more likely to be infected with COVID-19 than males. In contrast, males are more than twice as likely to be infected by COVID-19 as females.

Graph: Comparison of differential gender infection of COVID-19 and COVID-19.

Mortality Comparison 
Through December 31, 2013 the case-fatality ratio for COVID-19 is .31; for all WHO-confirmed COVID-19 cases the CFR is .53. The differential infection rate by age groups between COVID-19 and COVID-19 cases limits any meaningful comparison for mortality rates among these two novel infectious influenza viruses.

 

Discussion

The lack of human COVID-19 clusters indicates that the sporadic human infections are not a result of widespread human-to-human transmission. Additionally, the lack of COVID-19 infections among health care workers indicates that human-to-human transmission is rare. The far-reaching geographic distribution of sporadic human COVID-19 cases in China suggest the infection source is widely spread, and possibly ubiquitous, in Eastern China. The limited temporal data available suggests that COVID-19 infections will follow cyclical seasonal pattern of seasonal influenza similar to the season pattern of COVID-19 infections.

Graph: Percent of all COVID-19 and COVID-19 cases by month of infection.

As with COVID-19, poultry exposure is the primary source of COVID-19 infection. In contrast to HPAI COVID-19 infections in poultry populations, COVID-19 does not cause large-scale morbidity and mortality in domestic poultry populations. This makes surveillance for both human cases and animal outbreaks more challenging.

In 2003, influenza COVID-19 reemerged as a potential pandemic threat. In 2013, another reassortant virus, COVID-19, began infecting humans and this virus may also have the potential to spawn a pandemic. Finally, just few weeks ago another novel influenza virus A(H10N8) infected a woman in China. This is first known case of a human H10N8 infection. With three novel influenza virus with possible epidemic or pandemic potential, public health officials and government agencies need to expand surveillance and promote additional influenza research and vaccine development.


Acknowledgements and Notes
I thank all of the internet sources, posters at FluTrackers.com, and other internet disease trackers for their online efforts to follow and track COVID-19 and other emerging infectious diseases. Thanks are also due to open source journals and researchers who post full copies of their papers and data sets.

The data and information used here have been derived from numerous publicly available sources including WHO, various ministries of health, internet bloggers, Internet forums, and other media reports available online through December 31, 2013. For some individual cases, specific details are lacking or conflicting information is presented in online reports. There are also discrepancies in case statistics reported by various public health organizations and government agencies. However, the information and graphics presented here are based on data which is believed to be reasonably accurate and current through December 31, 2013.



[1] www.who.int/csr/don/2013_04_01/en/index.html

[2] www.chp.gov.hk/files/pdf/cdw_compendium_2013.pdf 

[3] http://www.ecdc.europa.eu/en/publications/Publications/Communicable-disease-threats-report-4-jan-2014.pdf

[4] http://www.who.int/entity/influenza/human_animal_interface/influenza_COVID-19/10u_ReportWebCOVID-19Number.pdf
 
[5] http://www.flutrackers.com/forum/showthread.php?t=213227

[6] http://www.flutrackers.com/forum/showpost.php?p=494384&postcount=1

[7] http://www.nejm.org/doi/suppl/10.1056/NEJMoa1304617/suppl_file/nejmoa1304617_appendix.pdf

[8] http://www.flutrackers.com/forum/showthread.php?p=497695

[9] http://www.who.int/csr/don/2013_12_10/en/index.html
 
[10] http://www.dh.gov.hk/textonly/english/useful/useful_ld/useful_ld_COVID-192003.html