Until the first signs of local spread, the strategy will continue to be containment of possible onward transmission from imported cases. This will involve contacts taking a supervised dose of the antiviral drug Tamiflu and medical surveillance at government clinics, rather than quarantine.

The decision was made based on new scientific insights and evolving global and regional situations. Health authorities isolated hundreds of guests and staff at Metropark Hotel, where the first imported case stayed. No quarantine orders were imposed for subsequent cases.

'If there are local cases, the government will stop tracing close contacts of patients and instead focus on treating those infected,' said Thomas Tsang Ho-fai, controller of the Centre for Health Protection (CHP).

The World Health Organisation said 46 countries had confirmed 12,515 cases including 91 deaths. Almost four of every five cases were in Mexico and the US, where the pig-derived strain was discovered last month. Canada, Britain, Spain and Japan also have a high number of cases.

Schools remain a particularly important consideration since outbreaks in Japan and the US originated in schools.

To slow the transmission of the disease when the first local case occurs, the government has considered suspending classes of all primary schools, kindergartens and nurseries for up to 14 days.

Since April 27, the CHP has sent at least 15 advisory letters to primary schools, kindergartens, child care centres and elderly and disabled homes.

The government said it would close schools when the first local case occurs that has no identifiable link, such as travel to an affected area in the previous seven days or exposure to a confirmed index case or secondary contacts.

Schools have been urged to review and activate contingency measures and to establish an effective communication mechanism with parents and staff.

Premises should be cleaned and disinfected. Schools should also remind parents that they should measure their children's body temperatures. Those with flu-like symptoms should wear a mask and seek medical advice as soon as possible. Children with fever and respiratory symptoms are strongly advised not to attend school until 48 hours after the fever has subsided.

Schools should ensure a sufficient stock of masks and teach children their proper use. Schools should have sent letters to parents to pay attention to the personal hygiene of their children.

A handbook on prevention of human swine flu in schools was compiled in mid-May. Similar guidelines were set out for offices and premises.

The CHP has placed special emphasis on minimising risks in the hotel and tourism industry, mindful that the first case of H1N1 flu involved a Mexican tourist who checked in at a local hotel before admitting himself to hospital.

Several sets of guidelines have been uploaded to the CHP website for preventing swine flu in the workplace. Each company should formulate plans to maintain operations.

Companies should identify personnel for essential services, prepare a staff roster, designate deputies of management, specify responsibilities of key management, conduct exercises and establish a stockpile of protective equipment.

Enterprises wishing to stock antivirals are recommended to do so through their doctors. Staff are also reminded to observe personal hygiene, such as washing hands and covering nose and mouth when sneezing or coughing.

'In essence, an explicit corporate infection control policy, good infection control practices, with sufficient personal protective equipment, are of paramount importance for protecting staff during influenza pandemic,' the CHP said.

As the disease progresses, the government said a range of public health measures may also be deployed. These include:

Active promotion and adoption of basic measures: personal measures such as hand hygiene and use of face masks, personal care for those who fall ill, environmental hygiene, etc.

Social distancing: school closure, workplace contingencies, cancellation of mass gatherings, etc.

Antiviral stockpile for treatment of patients, chemoprophylaxis of health care workers and essential service providers in the public sector

Vaccine administration

Mobilise private sector and NGOs to increase medical surge capacity

Private enterprises mobilising business continuity plans

Self-care: sick patients stay home until their illness is over for at least 48 hours

Risk communication to community segments

Secretary for Food and Health York Chow Yat-ngok has promised that Hong Kong's 7 million people may receive free swine flu vaccinations under the government's long-term strategy against a pandemic, although this measure was controversial.

Basic health measures that individuals can take could spell the difference. 'Stay informed and take heed of government announcements on school operations and social distancing measures,' the CHP added.

The world remains at flu alert level five, signalling an imminent pandemic. Symptoms of swine flu have been relatively mild and no worse than seasonal influenza for now.

But, in studies released by the New England Journal of Medicine, scientists pointed out that the new virus had similarities with ones that led to pandemics in the past century. They started off as mild but went through waves that became more lethal at their peak.