In the past few weeks, many places in Asia have experienced unprecedented outbreaks of avian influenza in poultry. The confirmed cases of H5N1 human infection in Vietnam and Thailand have raised serious concern over the possibility of an influenza pandemic.

I would like to give you a brief overview of the previous outbreak situation in Hong Kong.

We first experienced an H5N1 highly pathogenic avian influenza outbreak in poultry in 1997. At that time, our control strategy was complete depopulation. Since then, Hong Kong experienced three other outbreaks in the poultry population.

In each outbreak, we devised our control strategy in the light of the prevailing circumstances. The measures that we had adopted included quarantine, depopulation of affected chickens, and vaccination.

1997 outbreak kills 6 in HK

In the 1997 outbreak, we had 18 human cases of H5N1 infection, of whom six persons died subsequently. Investigation at that time revealed that contact with live poultry was believed to be the major route of infection. Man-to-man transmission was found to be inefficient.

In subsequent outbreaks of avian influenza in poultry, no human cases were identified. However, we do have two isolated human cases of H5N1 infections in early 2003 and one person died subsequently.

Preventive measures guard against outbreaks

Since 1998, we have put in place a series of preventive measures to guard against the occurrence of avian influenza outbreaks. The measures have been enhanced in the light of the experience learned over the years. Now, our preventive programme covers various areas including:

* vaccination;

* regulation of local farms including tightened biosecurity measures;

* import control;

* segregation policy;

* market rest days;

* hygiene requirements on wholesale market and retail outlets; and

* surveillance.

We introduced a vaccination programme for all our chicken farms in June last year and we also secured the Mainland's agreement and co-operation to vaccinate all chickens for export to Hong Kong.

At present, all the chickens available in the market have been vaccinated against H5 avian influenza.

In local farms, we have imposed tightened biosecurity measures to prevent the introduction of avian influenza viruses to farms. This includes the requirement that all farms should be bird-proof to prevent the introduction of viruses by wild birds.

To detect if local farms are infected, we place sentinel chickens  - unvaccinated chickens - in each batch of vaccinated chickens and monitor the health condition of the sentinels.

We also conduct testing on the antibody level of vaccinated chickens to ensure that the vaccine that we are using is effective in protecting our poultry against the disease. Prior to sale, each batch of chickens should also be subject to inspection and testing.

For imported chickens, they must come from registered farms recognised by the Mainland authority. Each consignment of imported chickens must be accompanied by a health certificate.

Our import-control programme includes testing of the antibody level of imported chickens, dead and sick bird monitoring and random screening testing of infection as appropriate.

To prevent the mixing of different types of avian influenza viruses which may result in reassortment into deadly viruses, we have implemented a segregation policy based on risk assessment.

As waterfowl are natural carriers of avian influenza viruses, all waterfowl in Hong Kong must be centrally slaughtered and no live waterfowl are allowed to be sold in retail outlets.

In addition, we also require that waterfowl offal must be separately and individually packed to prevent cross-contamination.

Given the scientific research that genetic material from H9 and H6 influenza viruses commonly carried by quail mixed with that from a goose H5N1 virus to form the lethal 1997 H5N1 virus, we require that all live quails must be segregated from live chickens from the farm to the retail levels. Now, no live quails are sold in our retail outlets.

Market rest days break virus cycle

At the wholesale and retail levels, we have market rest days to break the virus cycle and reduce the viral load there, if any. Each month, there are four rest days at our wholesale market and two matching rest days at all retail outlets. Trading activities must cease on the rest days and all live poultry in the retail outlets must be slaughtered and the premises must be thoroughly cleansed and disinfected.

We have also imposed stringent hygiene requirements on these premises. Examples include thorough cleansing and disinfection of transport cages and vehicles, cleansing of the faecal trays of cages housing chickens at retail outlets after operation everyday, no overcrowding of live chickens in the cages, et cetera.

In addition, we also require poultry retailers to surrender all live poultry for disposal on detection of even one dead bird with H5 virus isolated. The concerned outlet should then be thoroughly cleansed and disinfected.

Apart from the preventive measures, we have also put in place a very comprehensive surveillance programme which enables us to monitor human influenza activity and detect the presence of avian influenza viruses in our environment. This enables us to take responsive measures in a timely manner for the protection of public health.

On human influenza surveillance, our system enables us to monitor the disease trend and circulating influenza viruses. This programme covers a network of clinics, hospitals and laboratories in the public and private sectors.

On avian influenza surveillance, we started a comprehensive programme targeted at poultry at all levels from farms, the import level, the wholesale market and retail outlets in 1998.

This programme has enabled us to pick up any situation of concern at an early stage so that appropriate responsive measures can be taken to arrest the situation. To ensure timely detection of the presence of any avian influenza viruses in our environment and the possible reassortment of the viruses, we have also extended the programme to wild birds, waterfowl in recreational parks and pet birds available for sale in the market in 2003.

In 2003, we, in collaboration with a local university, conducted testing on about 34,000 samples. Our surveillance programme covers all types of avian influenza viruses.

Success must not breed complacency

These preventive and surveillance measures have reduced the risk of occurrence of large-scale avian influenza outbreaks in Hong Kong.

Yet, we are well aware that we must not be complacent. We have been on full alert to tighten up our line of defence at all fronts to prevent the occurrence of such outbreaks in Hong Kong. We also remain vigilant in guarding against any mutation or reassortment of avian influenza viruses that may have an impact on human health.

Close global collaboration is key

The latest incidents have posed serious challenges to our work in protecting public health. History tells us how detrimental an influenza pandemic can become.

Close international collaboration is crucial in the battle against the disease. I look forward to working with our neighbors and other parties of the rest of the world to deal with the threat that we are facing.