The Advisory Committee on Communicable Diseases (the Committee) of the Hong Kong Medical Association met Mr. Christopher WONG, Deputy Secretary (Food) of Food and Health Bureau (FHB), Dr. LEUNG Ting Hung, Controller, Centre for Health Protection, Dr. Allen CHAN, Senior Veterinary Officer of Centre for Food Safety, Food and Environmental Hygiene Department, and Dr. Elaine LEE and Dr. Benedict TSANG, Veterinary Officers of Agriculture, Fisheries and Conservation Department in an extended meeting held on 17 December 2013 to discuss on the surveillance and control measures required to protect our community against avian influenza (AI) H7N9.
1. The AI H7N9 outbreak appears to be at its zoonosis stage. Even
for the more recent cases in
2. The continuing occurrence of multiple poultry to human transmission
across Eastern and
3. History has shown us that more harmful mutant or re-assortment AI strains could emerge where the low pathogenic AI strains were allowed to persist and replicate in birds or poultry. Continuing vigilance is therefore warranted with the ongoing zoonotic outbreak.
4. Taking the difficulty in differentiating human H7N9 infections from other respiratory infections, less than desired performance of the current sampling and testing procedures with its predominant localization in the lower respiratory tract and the detection of other, often less severe, cases in the national influenza surveillance system, the reported figures likely represent only a portion of all human cases.
5. The Committee highlighted the new challenges posed by the emergent
H7N9 virus. The virus, though capable of causing lethal human diseases, is largely
silent among poultry. The term “lowly pathogenic” refers to its
pathogenicity in birds only. Many of the existing surveillance measures, like
the sentinel chickens, have been designed for “highly pathogenic”
AI viruses, like H5N1, which cause manifest disease among poultry. For H7N9,
the viral yield was low even with molecular polymerase chain reaction (PCR)
tools at putative poultry markets linked to the outbreak in
6. Some experts from
7. However, the existing data does not allow us to pinpoint the backyard poultry as the source or only source of the H7N9. From theoretical consideration of the transmission dynamics, huge aggregation of poultry may be more effective in sustaining low level of virus isolation than isolated chickens in backyard farms.
8. Poultry come from many different sources into
9. While live poultry from affected areas carries the highest risk, frozen poultry is not risk-free, as the AI virus may be preserved under frozen condition and can resume activity when the environment become warmer. Although gastrointestinal symptoms were not prominent among the reported human cases, this does Not exclude the possibility of enteric route of transmission altogether.
to FHB, around 7,000 live chickens (plus other minor poultry) are imported daily
to Hong Kong from registered farms in the Mainland, mainly in
11. About 10,000
live chickens are released from the 29 active licensed local farms every day.
This number may fluctuate according to market demand. All local chicken farms
are operating under stringent biosafety regulations. No backyard poultry are
12. To avoid cross-infection between imported and local chickens, different holding areas were built to separate the two categories of poultry, as well as other minor poultry, in the wholesale market. The chickens are normally sold within one to two days. The wholesale market, as well as the cages and vehicles used in the transportation of the poultry, are subject to thorough cleansing and disinfection every day.
13. Currently, there are 132 licensed live poultry retail outlets. Any unsold live poultry are slaughtered at the end of each day. Stringent hygienic measures with frequent cleansing and disinfection are undertaken at all levels of the live poultry supply chain.
14. For chilled
and frozen poultry imported from the Mainland. The supplying farms, namely associated
poultry farms, are subject to similar regulation and surveillance as those farms
supplying live poultry to
15. There is an ongoing surveillance program on wild birds covering both H5 and H7 AI. From available scientific data, the yield of H7N9 from sampling of wild birds is expected to be very low anyway.
16. The Committee
appreciated the efforts of the relevant bureau and departments in putting into
place those important safety measures as mentioned above. However, the Committee
also warned of an impending crisis in consumer confidence with the continuing
reports of cases in
17. Serological testing was raised by the FHB in the discussion with the Mainland authorities earlier. There had since been discussions among the experts about some technical issues. As these issues have largely been resolved now, the Committee urged the government to request our Mainland counterparts to introduce the serological testing without any further delay, AND in case of any difficulty in introducing such testing in the Mainland farms, testing should be initiated at our boundary control point and at local farms.
18. H7N9, being
of lower pathogenicity to birds, might not induce a very strong anti-haemoagglutinin
titre in birds as the more pathogenic H5N1. False positives can easily occur
with the usual haemoagglutination inhibition tests as a result of cross-reaction
to other more benign H7 viruses. However, H7 seroprevalence should NOT be high
19. In response to a question from FHB on whether there was a more robust alternative than enlarging the PCR viral sampling from 30 chickens per batch to, say, 120 in case of a positive result on serological testing from PCR-negative chickens, the Committee considered it very impractical and prohibitively costly to conduct a huge number of PCR tests to exclude a low percentage of potentially lethal H7N9 virus carriage in a serologically positive batch of chicken. While a suitable seroprevalence threshold would have to be set to allow for cross-reactions with other more benign viruses, it would be more cost-effective to slaughter the whole batch of possibly affected poultry if the seroprevalence suggested either a substantial probability of H7N9 or substantial lapses in the biosafety measures of the supplying farms.
20. With the continuing spread of the H7N9 virus among birds and poultry over a wide area, there is an obvious need to guard against possible introduction of the virus into the local farms. Besides separating imported and local chickens in the wholesale market, complete segregation of all personnel and vehicles handling imported chickens from those handling local chickens should be considered to avoid cross-contamination and back-tracking to local farms.
21. Should an
H7N9 outbreak of substantial size occur in
22. Although the government has a clear contingency plan for influenza pandemic threats, there is a need for ongoing assessment of the evolving situation. Suitable adjustments would also need to be made to meet the new challenges posed by the emergent H7N9 virus. No public health response system can be expected to have an unlimited surge capacity to cope with a crisis of any scale. With the limited capacities of the rapid testing system, isolation facilities and advanced life support machines, like the extra-corporal membrane oxygenation (ECMO), in the public sector, clear priorities should be set on the target groups for screening, isolation and advanced life support, so that suitable scaling down of coverage or rechannelling of less likely or milder cases to alternative facilities could be made to contain the workload in case of overwhelming demand.
23. With high tourist flow during Christmas and Chinese New Year holidays, visitors to affected areas would need to pay serious attention to various hygienic and precautionary measures as included under the current advice from the Centre for Health Protection: