Two waves of H7N9 – Credit CHP CDW
Hong Kong’s CHP publishes their Communicable Diseases Watch every two weeks, and today it includes an excellent overview of the H7N9 avian flu virus, and some notes on the recently emerged H5N8 virus as well. Being in close proximity to the source, and the recipient of 10 exported H7N9 cases during the first two waves, Hong Kong keeps close track of the developments with these viruses.
I’ve only included some excerpts, so follow the link to read:
Reported by Miss Amy Li, Scientific Officer, Respiratory Disease Office, Surveillance and
Epidemiology Branch, CHP.
According to the World Health Organization (WHO), avian influenza viruses have demonstrated a seasonal pattern in temperate zones in which animal outbreaks and human cases have been less frequent in summer months and more frequent in winter months. As the winter months approached, there has been an increase in sporadic human cases of avian influenza A (H7N9) infection in Mainland China. Two sporadic human infections due to a newly emerged highly pathogenic avian influenza H5N6 have also been detected in Mainland China in recent months. Besides, there were widespread outbreaks of avian influenza A(H5N8) among poultry in several Asian and European countries, as well as detection of H5N8 in birds recently in Washington and Oregon, United States.
Avian influenza A(H7N9)
The activity of avian influenza A(H7N9) remained at a relatively low level during the summer months in 2014. From July to August 2014, only two human H7N9 cases occurred in Mainland China (by onset date). Subsequent to these two cases, there have been 16 human H7N9 cases reported with onset dates since the beginning of September (as of December 23, 2014). These 16 cases occurred in Xinjiang (6), Jiangsu (3), Guangdong (2), Zhejiang (2), Beijing (1), Fujian (1) and Shanghai (1). Their ages ranged from seven to 81 years (median = 49.5 years) and the male-to-female ratio was 1 : 1. Of note, Xinjiang Uyghur Autonomous Region, which was not affected in both the first wave in 2013 and the second wave in 2014 and also not adjacent to previously affected areas, is a newly affected region in Mainland China, with a total of eight cases since July this year. WHO commented that this indicated that the virus continues to circulate and is potentially widespread.
Cumulatively, a total of 469 confirmed human H7N9 cases have been reported since March 2013, including at least 184 deaths (as of December 23, 2014).These included 454 cases in Mainland China and 15 cases exported from Mainland China to Hong Kong (10), Taiwan (4) and Malaysia (1). Figure 1 shows the epidemic curve of human cases. There were two distinct waves of human infections, one occurring from March to June in 2013 and another occurring from October 2013 to June 2014. A total of 318 cases were reported in the second wave, which greatly exceeded the total of 133 cases reported in the first wave. The age and sex distribution of the cases reported in the second wave remained largely comparable to that of the first wave.
Nonetheless, Guangdong, which was not affected in the first wave, had its first case detected in July 2013 and subsequently became the most affected province in the second wave. Thirty-four percent of the cases recorded in the second wave occurred in Guangdong. Moreover, all the 10 cases notified in Hong Kong were imported from Guangdong during the second wave.
Regarding H7N9 in poultry and birds, the World Organisation for Animal Health (OIE) reported detection of positive H7 samples in a market in Henan on July 9, 2014. Separately, the Ministry of Agriculture in Mainland China conducts regular testing to monitor the presence of H7N9 in poultry and birds. In November 2014, a total of 151 583 samples (103 050 serum samples and 48 533 virological samples) were collected from 5 326 locations*. Among these samples, 12 serum samples from Henan and seven serum samples from Guangdong were tested positive for H7 by serological test, and two samples from Fujian as well as one sample from Qinghai were tested positive for H7N9 by virological test.
Based on the seasonal pattern of avian influenza viruses, it is likely that the disease activity of H7N9 in the Mainland may further increase this winter and heightened vigilance is warranted.