Thursday, January 19, 2017

HK CHP Epidemiological Assessment Of H7N9

Credit CHP CDW  Vol 14 Issue 1


With China's 5th H7N9 winter epidemic off to an unusually early and vigorous start, and already 4 imported cases detected in Hong Kong, their Centre for Health Protection is on heightened alert and is actively warning residents to take precautions over the New Year's Spring Travel Holiday (see CHP alerts public to high avian influenza A(H7N9) activity in Guangdong).
As discussed in Beneath The H7N9 Pyramid, getting reasonably good surveillance numbers out of any disease outbreak is always a challenge, but China's penchant for releasing case information in large batches - often weeks after the fact (see HK CHP: China Reports An Additional 83 H7N9 Cases For December) - makes real-time assessments of their epidemic very difficult. 

That said, we have no indication of sustained of efficient human-to-human spread, and most cases still appear to be linked to exposure to (asymptomatically) infected poultry.  The caveat being (see MMWR: Assessing The 4th Epidemic Wave Of H7N9 In China), influenza viruses are constantly changing, and what has been true up until now may not hold true forever.

Today Hong Kong's CHP has published an epidemiological update on the H7N9 virus in their Communicable Diseases Watch journal, which is published every two weeks.  While very `current', the article warns `Some of the cases occurring in January 2017 have not been reported yet and hence not included.'

Some excerpts from the report follow,  but you'll want to hit the link to read it in its entirety.

 Update on situation of avian influenza A(H7N9)
Reported by Dr Albert AU, Senior Medical and Health Officer, and Dr Francis WONG, Medical and Health Officer, Respiratory Disease Office, Surveillance and Epidemiology Branch, CHP.

The activity of avian influenza A(H7N9) viruses has been increasing markedly since the end of 2016, indicating the start of a new wave of human infection this winter. There has been large increase in reports of human infections with avian influenza A(H7N9) in various parts of Mainland China recently.We reviewed the latest situation of H7N9 in this article.

Epidemiological situation Human infections

The first two human H7N9 cases in the current wave reported by the National Health and Family Planning Commission (NHFPC) occurred in October 2016. The number of cases has been increasing markedly since November. The NHFPC has reported that six and 106 cases were detected in Mainland China in November and December 2016 respectively. This wave has been progressing much faster than that in the previous winter. In the fourth wave which occurred between late 2015 and mid-2016, only six cases were reported in the first three months since the first report in September 2015, as compared with 114 cases in the first three months in this wave. 

Since October 2016, 143 human H7N9 cases have been reported by health authorities in 11 provinces/municipalities in the Mainland* (Figure 1), including 57 cases in Jiangsu (江蘇), 26 cases in Guangdong (廣東), 22 cases in Zhejiang(浙江), 14 cases in Anhui (安徽), 7 cases in Jiangxi (江西), 4 cases each inHunan (湖南) and Shanghai (上海), 3 cases each in Fujian (福建) and Guizhou(貴州), 2 cases in Shandong (山東), and one case in Hubei (湖北). Thereported cases in Guangdong occurred in various areas including Dongguan (東莞), Foshan (佛山), Guangzhou (廣州), Jiangmen (江門), Jieyang (揭陽),Meizhou (梅州), Qingyuan (清遠), Shenzhen (深圳), Zhaoqing (肇慶) andZhongshan (中山). Among these 143 cases, their ages ranging from 23 to 91(median=54). The male-to-female ratio was about 2:1. Most cases presented with severe conditions.

According to the information from the NHFPC, among the 114 cases detected from October to December 2016, at least 85 (75%) were known to have exposure to poultry or poultry markets before onset of symptoms while the sources of infection of most of the remaining cases were reported to be under investigation.


Since the emergence of human H7N9 infections in Mainland China in March 2013, at least 947 human H7N9 cases have cumulatively been reported globally. In the previous four waves, the majority of cases occurred between December and April (Figure 2). Apart from an asymptomatic case with exposure to infected poultry in Macau, all the remaining cases occurred in Mainland China with 28 cases exported to other areas outside Mainland China.The case fatality rate was about 40%. 

In Mainland China, the provinces with the greatest number of reported cases included Zhejiang (25%), Guangdong (23%) and Jiangsu (17%). In Hong Kong, since the detection of the first imported case in December 2013, 20 human H7N9 cases (including seven deaths) have been confirmed so far.Among them, 19 were imported from Guangdong and one was imported from Jiangsu.

Public health risk assessment

According to the World Health Organization, most human cases were exposed to avian influenza viruses through contact with infected poultry or contaminated environments, including live poultry markets. Since the viruses continue to be detected in animals and environments, further human cases are expected to occur from time to time. Locally, since the H7N9 virus continues to be detected in poultry and environments in Mainland China especially Guangdong, further human cases are expected in affected and possibly neighbouring areas. In the past few years, most human H7N9 cases in the Hong Kong were detected in the first quarter of a year and were imported from Guangdong. In view of the heavy trade and travel between Mainland China and Hong Kong, further sporadic human cases and affected poultry imported to Hong Kong every now and then are expected, especially in the coming few months.

Even though small clusters of human H7N9 infections have been reported previously including those involving healthcare workers, current epidemiological and virological evidence suggests that H7N9 viruses have not acquired the ability of sustained transmission among humans, thus the likelihood of human-to-human transmission of avian influenza viruses is low.With oseltamivir prophylaxis and medical surveillance of the close contacts of any confirmed cases, the risk of secondary spread from cases imported into Hong Kong is considered to be low at the present moment provided that the avian influenza viruses still have not acquired the ability of efficient human-to-human transmission

(Continue . . .)