Advisory Council on Food and Environmental Hygiene

Report on the Recent Avian Influenza Outbreak


This paper reports the recent avian influenza outbreak and the follow-up actions. Members are invited to note the latest developments.

The Outbreak

(a) Local farms

2. In the early morning of 1 February, the Agriculture, Fisheries and Conservation Department (AFCD) detected a batch of chickens suspected to have been infected with disease during overnight inspections at the Cheung Sha Wan Temporary Wholesale Poultry Market. An abnormal number of chickens died when the batch of chickens was detained at AFCD's New Territories North Animal Management Centre. AFCD immediately took faecal samples from the chickens for testing and the whole batch of chickens was destroyed.

3. The same day, AFCD traced these birds to the farm of origin in Kam Tin and found a large number of dead chickens on the farm. They immediately stopped the farm from sending any chickens to the market. Investigations were carried out in the farm and additional samples were collected for laboratory tests. More dead chickens were found on the farm on 2 February. Test result showed that the chickens died of avian influenza. We therefore decided to depopulate the farm. The exercise was completed on 3 February. At the same time, we immediately stepped up surveillance in all local farms and the wholesale and retail markets.

4. On 4 February, two farm owners in Kam Tin reported to AFCD the presence of disease in their chickens. Subsequent investigations confirmed that both farms were infected with H5 influenza virus. Another chicken farm in Hung Shui Kiu was also found infected. All those farms were declared infected places and all the chickens therein were destroyed. To minimize the risk of spread from the Kam Tin area, the Administration put all 22 farms in that area under quarantine and prohibited the supply of chickens from those farms to the market. In addition, two farms outside the Kam Tin area (one in Pak Sha and the other in Lau Fau Shan) were also placed under quarantine as a precautionary measure, pending investigation into the signs of disease amongst the chicken population.

5. On 9 February, we put into place a number of measures to tighten the inspection and testing of chickens from local farms (please see paragraph 12 for details). By 18 February, another 11 quarantined farms within the Kam Tin Area were found to have been infected, leaving only eight farms in the Kam Tin Area unaffected. All known infected farms were depopulated and after considering the advice of the Expert Working Group on Avian Influenza that the remaining farms were likely to be infected, the Administration decided on 19 February to depopulate these farms also. Subsequent test results have confirmed that all but four farms in the quarantine area in Kam Tin were infected. As regards the two quarantined farms in Lau Fau Shan and Pak Sha, AFCD concluded, after thorough investigation, that the chickens there were not infected with H5 virus and they were allowed to send birds to market under strict controls on and after 19 February.

6. On 20 February, a farm owner at Pak Sha reported to AFCD that there were chicken deaths on his farm. AFCD immediately went to the farm to investigate and found 140 dead chickens. Samples were taken from the farm for testing and the farm was closed at once. After further investigation, AFCD's testing demonstrated that the farm was infected with an H5 virus and it was depopulated on 23 February. Initial investigations did not reveal any direct link between this infected farm in Pak Sha with the farms in Kam Tin or the earlier quarantined farm in Pak Sha.

7. On 3 March 2002, AFCD detected 100 dead chickens on another farm in Pak Sha. Tests showed that the farm was infected with an H5 virus. Action was taken on 5 March 2002 to depopulate the farm.

8. As at 5 March 2002, a total of 25 local farms (including 22 in Kam Tin, one in Hung Shui Kiu and two in Pak Sha) have been depopulated. Some 900,000 chickens in these farms were destroyed.

(b) Markets

9. From 3 to 6 February, chickens showing clinical signs of avian influenza were found in individual stalls in several markets. The chickens were destroyed and the stalls concerned were thoroughly cleansed and disinfected. However, chickens in the retail markets generally did not show any signs of disease. Some 6,000 live birds from 13 chicken stalls in the Tsuen Wan Market and 9 chicken stalls in other markets were slaughtered. The Government and the live poultry retail trade both considered that an extra rest day for cleansing would help maintain retail markets in a hygienic state. Thus an additional rest day was held on 8 February. Since then, the state of chicken health in the retail markets has been generally normal.

10. As regards the Cheung Sha Wan Temporary Wholesale Poultry Market, we found about 200 dead chickens on 21 February. Test revealed that the chickens were infected with avian influenza. The concerned area of the wholesale market was thoroughly cleansed and disinfected. 24 and 25 February were also rest days for the wholesale market and thorough cleansing and disinfection took place on these days.

(c) Testing results

11. We are now conducting gene sequencing analysis of the H5 viruses isolated in the outbreak. The test results of samples taken from the first two depopulated farms show that the virus is an H5N1 virus but is not the same as the H5N1 virus that affected human health in 1997. Experts also hold the view that there is no evidence to date to show that the virus affecting the chicken population this time would affect humans. The full testing results would be available by end of March.

Improvement measures

12. We identified a number of measures for immediate implementation as regards chickens from local farms. These measures were implemented on 9 February 2002 -

  1. In addition to conducting blood testing for H5 antibody no more than five days before local chickens are released to the market, an additional blood test is conducted before the chickens are sold to retail outlets. This second blood test is done at the Cheung Sha Wan Temporary Wholesale Poultry Market, through which all chickens from local farms must now be sold. Only chickens that pass the test are allowed to be sold to retailers;

  2. When chickens from local farms are delivered to the wholesale market, AFCD staff verify the farm of origin, the number of birds, and the documents certifying that the chickens have undergone the first blood test. They then check for dead birds in the consignment and collect blood samples before the chickens are allowed to be unloaded;

  3. Chickens from local farms are directed to a designated area in the Cheung Sha Wan Temporary Wholesale Poultry Market and are not allowed to be mixed with imported chickens until the second blood test results are available;

  4. Each vehicle is only used for transporting consignments of chickens from one single local farm to the Cheung Sha Wan Temporary Wholesale Poultry Market to reduce the probability of cross-contamination; and

  5. All vehicles used for transporting chickens from local farms must be cleansed thoroughly in the Cheung Sha Wan Temporary Wholesale Poultry Market before they are allowed to collect clean cages for transportation of chickens from local farms to the wholesale market.

In addition, AFCD deployed staff to oversee on site the loading and transportation of local chickens during the peak season for sale of live chickens prior to the Lunar New Year.

13. Furthermore, we have identified areas where local farm biosecurity can be improved. AFCD is maintaining an active dialogue with the local chicken farmers with a view to upgrading farm bio-security and enhancing hygiene standards of local farms.

Further Investigation

14. The Secretary for the Environment and Food has set up an investigation team to establish the cause(s) leading to the current influenza outbreak in local farms and to recommend measures to reduce the likelihood of such incidents recurring in future. The team is headed by the Director of Agriculture, Fisheries and Conservation and comprises an avian influenza expert, a veterinary surgeon, a member of the Advisory Committee on Agriculture and Fisheries, the Deputy Director of AFCD and the Deputy Director of FEHD. A report is expected to be submitted to the Secretary in six weeks. We will report the findings of the investigation team to the Council.

Environment and Food Bureau
March 2002