Since December 2003, highly pathogenic H5N1 avian influenza viruses have swept through poultry populations across Asia and parts of Europe. The outbreaks are historically unprecedented in scale and geographical spread. Their economic impact on the agricultural sector of the affected countries has been large. From December 2003 to mid-July 2005, outbreaks of avian influenza A(H5N1) in poultry occurred in nine countries (Cambodia, China, Indonesia, Japan, the Republic of Korea, the Lao People's Democratic Republic, Malaysia, Thailand and Viet Nam). Since late July 2005, outbreaks in domestic poultry as well as wild birds have been reported in the Russian Federation, Kazakhstan, Romania, Mongolia, Turkey and Croatia. In addition, during this period outbreaks in poultry have increased again in Indonesia, Thailand, Viet Nam and China.Three contiguous WHO regions – Western Pacific, South-East Asia and Europe – now have H5N1 activity in wild fowl and poultry stocks. Evidence shows that the H5N1 virus is most likely endemic in many parts of Asia. It has established an ecological niche in poultry, making it extremely difficult to control outbreaks. Outbreaks have recurred despite aggressive control measures, including the culling of more than 140 million poultry as of September 2005.
Human cases, with an overall fatality rate around 50%, have been reported in Cambodia, Indonesia, Thailand and Viet Nam. Almost all human infections can be linked to contact with infected poultry, but isolated instances of inefficient human-to-human transmission may have occurred in Viet Nam in 2004, and possibly in Thailand and Indonesia. Influenza viruses are genetically unstable and their behaviour cannot be predicted. The risk of further human cases persists, as do opportunities for a human pandemic strain of the virus to emerge. For these reasons, the current outbreaks of influenza A(H5N1) in poultry and humans in Asia, has moved the world closer to a pandemic than any time since 1968, when the last such event occurred.
The WHO Western Pacific Regional Office emphasizes the following strategic approach to control the regional outbreak of avian influenza A(H5N1) and reduce the risk of an influenza pandemic.
AI Weekly Update Number 319 (17 February 2012)
1. Latest information on Human Avian Influenza cases
Since 2003 to 16 Feb 2012, the number of cases reported from 15 countries worldwide is 584 and 345 were fatal (CFR 59.1%). Among the countries with more than 10 reported cases, Cambodia had the highest CFR of 89.4% (17 out of 19).
Age distribution of the reported cases ranged from 3 months to 81 years old (median 19 years, n=561). The age group with the largest number of cases was 20-29 years of age (23.2%, 130/561), relative to other age groups (0-4; 5-9; 10-19; 30-39; 40-49; 50-59; 60-69; 70+ years). The highest CFR (73.3%) was among persons 10-19 years of age and lowest was among persons 0-4 years (25.7%) and persons 70+ years old (25.0%). 53.8% of the cases were female (301/559).
Table 1: Cumulative Number of Confirmed Human Cases (C) and Deaths (D) of Avian Influenza A (H5N1) Reported to WHO
2. Latest Human H5N1 cases in countries affected in 2012 (Updated 16 February 2012)
Cambodia. The latest reported case in 2012 was 2 year old male from Banteay Meanchey Province. He developed symptoms on 3 Jan, admitted to hospital on 9 Jan, and died on 18 Jan. The boy was exposed to sick poultry in his village. The National and Local Rapid response teams are conducting outbreak investigation and response
China. The latest reported case is 39 year old male, from Guiyan city, Guizhou province. He developed symptoms on 6 Jan, admitted to hospital, died on 22 Jan. The case was laboratory diagnosed by Guizhou CDC and confirmed by China CDC on 22 Jan. Investigation into the source of infection is ongoing. Close contacts of the cases are being monitored and to date all remain well.
Egypt. Two cases are reported on 19 Jan 2012. The first case is 2 year old female from Cairo Governorate. She was an outpatient with ILI symptoms at Helwan Fever Hospital on 30 Oct 2011. This case was confirmed by the Central Public Health Laboratory through periodic testing of samples collected from sentinel ILI surveillance sites. She had a history of exposure to backyard poultry. The second case is a 31 year-old male from Fayium governorate. He developed symptoms on 1 Jan 2012, and is still hospitalized under the critical care unit. He had exposure to backyard poultry.
Indonesia. The latest reported case in 2012 is a 5 year-old female. She was identified by a surveillance team during an investigation in the area on 7 Jan and referred to a hospital. 13 Jan, she had breathing difficulties. Her condition deteriorated and she died on 16 Jan. Epidemiological investigation indicated that she was a family contact of the case who died on 7 Jan (23 y-o male) and frequently had direct contact with the same pigeons as that case and the same household environmental.
Viet Nam. The case was a 26 year-old pregnant female from Thanh Tri district, Soc Trang province. She developed symptoms on 23 January 2012 and sought treatment at a district hospital on that day; on 25 January she was admitted to Back Lieu Provincial Hospital and had a caesarean section on the same day. While she was treated with Tamiflu on 27 January, she died on 28 January. Confirmatory test results for influenza A (H5N1) were obtained on 30 January by Pasteur Institute, the WHO National Influenza Centre in Ho Chi Minh City, Viet Nam. Samples from the newborn infant of the fatal case taken for laboratory testing tested negative for H5N1. The case had slaughtered and eaten sick chickens and recently there were sick and dead poultry around her house. MoH, the local health sector and Pasteur Institute in Ho Chi Minh City are conducting epidemiologic investigation and strengthening surveillance and response activities.