Vivien010

The first officially reported human case of infection from a reassortant avian influenza A(H7N9) virus was from the People’s Republic of China (China) in March of 2013, although human H7N9 infection may have occurred in or near Hong Kong as early as 2007 (FAO ID event 220957). Since 2013 the World Health Organization (WHO) has officially reported 808 human cases of H7N9 as of December 23, 2016. In the past few days, an additional 13 H7N9 cases have been reported by public health officials in China but have not yet been published by the WHO. Of these 821 cases, 696 have onset or reporting dates prior to December 31, 2015. The total number of reported H7N9 cases in 2016 is 125.

Geographic Distribution 

All 125 human cases of H7N9 in 2016 were reported from China. These cases have been reported from 18 provinces and special administrative regions. More specific geographic location information was available for 117 of these cases, the remaining 8 cases were only reported from a specific province; Anhui 2, Hebei 2, Fujian 1, Hubei 1, Shandong 1, and Zhejiang 1. The map below depicts the provinces and special administrative regions with reported 2016 cases. Dots indicate the locations of individual or multiple cases reported in 2016. In 2016, these cases all occurred in the Western portion of China.

From 2013 to 2015, the median age of H7N9 infected males was 57.5 years with ages ranging from 1 to 91 years old. For females during that period the median age was 54.5 with ages ranging from less than year to 85 years old. The age distributions by gender for 2016 is similar. The chart below compares age categories for 2013-2015 and 2016. In 2016, infected individuals were somewhat younger than previous years.

Gender

Between 2013 and 2015, 471 of the reported cases were male (68%) and 220 of the reported cases were female (32%). The genders of the remaining cases were not published. Among the 125 cases reported in 2016, 72% (85) were male and 28% (33) were female. Seven cases do not have a reported gender.

It seems that males are far more likely to contract H7N9 infections than females. Because almost all cases are associated with exposure to infected poultry, it is possible that different gender roles expose males more frequently to affected poultry than females. 

Between 2013 and 2015, 143 of the 696 reported H7N9 cases were reported as fatal. These data would suggest a minimum case fatality risk (CFR) of .21.

The CFR, as defined here, is the conditional probability of death from an H7N9 infection, a ratio between H7N9-caused deaths and recoveries/asymptomatic cases. Because follow-up reporting is lacking in many of these cases, the actual number of deaths versus the number of recoveries is uncertain. Very few of the cases in the period from 2013 to 2015 were officially reported as recovered (only 133).

In 2016, 29 of the 125 cases were reported as fatal. At face value, the CFR for 2016 is .23 but it is likely to be higher since many of the recently reported cases are currently being treated.

Most of the reported human H7N9 infections in 2016 result from zoonotic transmission of the virus from domestic poultry. Public health reports in 2016 rarely indicate the possibility of human-to-human transmission among confirmed H7N9 cases which would signal a cluster of cases. 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 link.

Based on family ties or restricted geographic area, potential human H7N9 clusters in 2016 include the following. In February 2016 infected individuals in several locations may represent multiple clusters, two siblings in Suzhou Jiangsu, several family members in Wuxi Jiangsu, and several unrelated individuals in Fuzhou Fujian. Several family members from Tahie Jiangxi were reported as H7N9 cases in April. Two cases from Hebei in July of 2016 may represent a cluster. Recently, two infected individuals from Kunshan Jiangsu were reported in November and three cases in Hefei Anhui in December, with no other details are available.

Most of the human H7N9 case reported in 2016 are sporadic infections. As noted above, a few clusters of cases suggest that human-to-human transmission may have occurred but did not result in sustained human-to-human transmission. H7N9 cases seems to occur on an annual cyclical basis that follows the pattern of season human influenza infections. As depicted in the chart below, H7N9 cases were frequent from week numbers 1-23 and started increasing again in week number 46. The seasonal fluctuation in human infections indicates that more H7N9 cases can be expected in the coming months. While the number of H7N9 cases declined in 2016 compared to earlier years, the potential for a deadly epidemic or a possible H7N9 pandemic continues to exist.

 Chart: Epidemic curve of human H7N9 cases in 2016.

Note: The information presented and discussed here is based on a compilation of publicly available data sources including WHO, Food and Agriculture Organization of the United Nations, and various public health agencies supplemented by media reports as available.

Influenza A(H5N6) is an emerging novel avian influenza that apparently derived from a reassortment of A(H5N1) with A(H6N6). H5N6 was first reported in domestic poultry in early 2014 from Laos, Vietnam, and China. Since then it has continued to be widely reported from domestic flocks in these countries (primarily China).

In April 2014, the first case of a human infected with the H5N6 influenza virus was reported from Sichuan Province in China. Since then, seven additional human cases have been reported, all from China. The most recent case was reported from Jieyang, Guangdong Province a few days ago. Of these eight cases, six have been reported by the World Health Organization (see links below).

Based on onset dates two of these cases occurred in 2014, four in 2015. Onset dates for the two most recent cases have not yet been reported. Among these cases are five males and three females. One of the females was pregnant. Her child was delivered by caesarian section and the woman is apparently still under treatment. Media reports indicate that the child was not infected.  Ages range from 25 to 50 years old. Five the eight have died according to media reports.

To date, there is no evidence of human-to-human transmission among these eight cases of H5N6. The fatality rate is high, but there are too few cases to project a fatality rate for a larger population of infected individuals. It is not known if subclinical cases of H5N6 are occurring. No asymptomatic cases have been reported and there are no reports of seroprevelance studies of H5N6 among humans.

As shown in the map below, these eight cases from the past two years are widely scattered over China. The map also depicts the location of reported H5N6 outbreaks in poultry flocks in southern China and northern Laos. Like the distribution of human cases, domestic flocks infected with H5N6 are widely scattered across a large area. The wide-spread geographic distribution of infected poultry along with the dispersed nature of human infections in this area suggests that more human cases are likely to be reported in the future. With such a large animal reservoir this influenza virus could reassort and become more easily transmitted to humans. Were H5N6 to pick up the ability to transit easily among humans, H5N6 could become a deadly pandemic virus. 

Human Infection with a Novel Avian Influenza A(H5N6) Virus (case 4)

Reassortant Highly Pathogenic Influenza A(H5N6) Virus in Laos (May 2015)

Two novel reassortants of avian influenza A (H5N6) virus in China (May 2015)

Human H5N6 Influenza Virus Infection: New Disease Outbreak (August 2015)