A Demographic and Geographic Overview of the first 100+ Human Cases of Influenza A(H7N9) in the People?s Republic of China, April 22, 2013

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Laidback Al

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A Demographic and Geographic Overview of the first 100+ Human Cases of Influenza A(H7N9) in the People?s Republic of China, April 22, 2013

April 22, 2013, 05:01 PM

A Demographic and Geographic Overview of the first 100+ Human Cases of Influenza A(H7N9) in the People’s Republic of China, April 22, 2013
Laidback Al, Senior Moderator, www.FluTrackers.com

Abstract

A novel influenza virus was discovered infecting humans in mid-February in the People’s Republic of China (China) and was reported publicly on March 31, 2013. This influenza virus, Influenza A (H7N9), has infected more than 100 individuals in China since mid-February. It has not yet been reported outside of China. Among the reported cases, it is virulent with a high mortality rate. Men are twice as likely to contract the virus as women. Most reported cases are elderly individuals. Although limited human-to-human transmission may have occurred among these cases, the reported data does not indicate sustained human-to-human transmission.

Introduction

Since the first official report of human infections of Influenza A(H7N9) in China on March 31, 2013 (link) more than 100 human cases of influenza A(H7N9) have been reported from China to the World Health Organization (WHO) as a reportable disease under International Health Regulations. Data incorporated into this discussion is primarily based on provincial and municipal Departments of Health announcements, official media reports, and updates by WHO. There is no official line list of human cases infected with H7N9 that is publicly available although the Western Pacific Region of WHO published a table of cases that was current through April 17, but has now removed that page from the web.

The information discussed here is based on information compiled by members of FluTrackers.com. FluTrackers (FT) is also maintaining a current numbered list of cases (FluTrackers link). The case numbering sequence used by FluTrackers is based on the date of official report, not onset dates. This list corresponds to the cases reported to WHO by China (WHO archive link), although this discussion includes the asymptomatic 4-year-old boy from Shunyi district, Beijing who tested positive for H7N9 but is not included in the official case count (FT Case Number 61).

Number of Reported Cases

As of April 22, 2013, there have been a total of 106 cases of H7N9 reported from seven provinces and municipalities in eastern China; Anhui, Beijing, Henan, Jiangsu, Shandong, Shanghai, and Zhejiang. The cumulative count of these cases is graphed by onset date below. The date of symptom onset has not been publicly reported for 13 cases.

Gender and Mortality Statistics

The gender of two retrospectively confirmed cases from Shanghai municipality has not reported. Of the remaining 104 cases, 33 are female and 71 are male. Among the reported cases infection in males is more than twice that of females.

Age Statistics

The ages for the cases where age is reported range from 2 to 89 years old. The age distribution is skewed toward the elderly. Only four pediatric cases have been reported. They include two males, a 2-year-old and 4-year–old from Shanghai, and a 4-year old boy and a 7-year old girl from Beijing. The 4-year-old boy was asymptomatic. None of these children have died.

As noted by many internet commentators, there is a disproportional number of elderly people infected with this virus. The graph below compares the age group distribution of H7N9 cases with the overall population distribution of China.

Onset and Hospitalization

The incubation period for H7N9 is estimated to be seven days according to a China CDC epidemiologist (link). Individuals seem to seek treatment or are hospitalization between 1 and 19 (?) days after onset. Since April 1, 2013, the average number of days from onset to hospitalization is 3.6 days for 29 cases with reported dates of hospitalization.

Severity and Mortality

Of the 106 cases officially reported by China, as of April 22, 2013, there have been 21 deaths and 12 patients who have discharged (FT link). The remaining 73 cases are apparently still hospitalized, some cases for as long as several weeks.

Clusters of Cases

A cluster is defined by WHO as two or more cases of confirmed, probable, or suspected Influenza 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 (WHO link).

At least three human clusters have been identified among the reported cases from China, a family cluster of three males that included one of the first reported cases, a husband and wife from Shanghai, and two children in the same neighborhood in Beijing.

Cluster 1: Lee family, Shanghai (Confirmed)

The first A(H7N9) case officially reported from Shanghai, an 87-year-old male, was one of three family members admitted to a hospital in mid to late February. Mr. Lee died on March 4. He was the father of the other two male cases. One of the brothers, a 55-year-old, died. The other brother, a 69-year-old, survived. Of the three cases the 87-year-old father was initially confirmed with H7N9. The two sons were retrospectively confirmed as cases of A(H7N9).

Cluster 2: Gu Family Cluster, Shanghai (Confirmed)

This cluster also represents a family cluster of a husband and wife from Shanghai. The wife had symptoms starting on March 27, was hospitalized, and died on April 3rd. The husband experienced symptoms on April 1st, was hospitalized on April 4th, and apparently is still being treated. This cluster could be human-to-human or infection from a common non-human host (FT link, FT link).

Cluster 3: Beijing Neighborhood Cluster (confirmed)

Two children who are neighbors in Houshayu in Shunyi District, Beijing were confirmed with H7N9. A 7-year-old girl, started experiencing symptoms around April 11 and was hospitalized (FT link). A neighbor child, a 4-year-old boy, tested positive for A(H7N9) but was reported asymptomatic (FT link). Media reports indicate that the parents of the girl were engaged in the poultry business and the parents of boy may have purchased some poultry from the girl's parents. There are conflicting reports that one or both parents of the girl, who were keeping her company in the hospital, were exhibiting ILI symptoms.

Potential Geographic Clusters – Shanghai Municipality
The provinces of Shandong, Anhui, and Henan have only reported geographically scattered cases. The Shanghai municipality has reported 33 cases. Based on the fact that many of these individuals were treated at different hospitals, these cases may have come from different areas in Shanghai. Shanghai is one of the largest cities in the world with a population of more than 23 million, so epidemiological links between any of the 33 cases (besides the family cluster that included the initial case) would have to be identified in the department of health reports.

Potential Geographic Clusters - Zhejiang and Jiangsu Provinces

Twenty-six confirmed A (H7N9) cases have been reported from Hangzhou, Zhejiang. Another six cases have been reported from Huzhou, Zhejiang. The reports are not clear if all of these cases are from the metropolitan/urban areas or outlying county areas. About 90% of the reported cases from Zhejiang are from these two locations. Two cases are reported from Jiaxing, Zhejiang. At least 9 A(H7N9) have been report from various districts in Nanjing, Jiangsu. Two cases have been reported from both Suzhou and Kunshan, Jiangsu. China has not reported any clusters among these cases.

Geolocation of Cases

The 106 cases are concentrated in several provinces and municipalities of eastern China as shown in the maps below.

Virus sequences
Only five human A(H7N9) sequences have been released by China to date, all from widely separated geographic areas except for the two samples from Shanghai.

Summary

A novel influenza virus, influenza A(H7N9), was reported from China at the end of March 2013. As of April 22, 2013, 106 confirmed cases of influenza A(H7N9) have been reported from China in the past four weeks. To date, no cases have been reported outside of China. The case-fatality ratio is .20. Almost twice as many males as females have been reported infected with the virus. Elderly individuals are disproportionately represented among the cases in relation to the overall population in China. The infection is virulent among most reported cases. WHO reports that as many 70 individuals are still hospitalized. Based on information provided by public health officials in China, there is little evidence of human-to-human transmission and no evidence of sustained human-to-human transmission, although the current geographic clusters need close monitoring.

Additional Resources

List of cases: Flutrackers H7N9 Case List (link)

Links with Demographic Graphs and Charts

Avian influenza A virus H7N9... by Dr. Ian M. MacKay (link)

Random Analytics: Avian Influenza A(H7N9) Virus (to Sun 21 Apr 2013) by Shane Granger (link)

Google Map of Case Locations: H7N9 Map by Feng (includes some H1N1 cases on the map) (link)

Acknowledgements and Notes
I thank all of the posters and moderators at FluTrackers.com for their efforts at tracking this novel infectious disease outbreak.

The data and information used here have been derived from numerous publicly available online sources and internet media reports. For some individual cases, specific details are lacking or conflicting information is presented in online reports. However, the information and graphics presented here are based on data which is believed to be reasonably accurate and current through April 22, 2013.
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Last edited by Laidback Al; April 22, 2013, 08:50 PM. Reason: more typos
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