Causative agent

Various strains of seasonal influenza viruses may cause influenza infection. Influenza A (H1N1) 2009 virus (i.e., human swine influenza virus) is one of them.

Confirmed human cases of influenza A(H1N1) 2009 were firstly found in Mexico and the United States in April 2009, and then spread to many countries/regions worldwide and emerged to cause the pandemic in mid 2009. The World Health Organization announced in August 2010, that the world was no longer in phase six of the influenza pandemic alert and was moving into the post-pandemic period. Based on experience with past pandemics, this virus is expected to take on the behaviour of a seasonal influenza virus and continue to circulate in the community for some years to come.

Influenza A(H1N1) 2009 virus has now become one of the common seasonal influenza strains in Hong Kong.

Clinical features

The symptoms of influenza A(H1N1) 2009 are similar to influenza caused by other seasonal influenza viruses and include fever, cough, sore throat, runny nose, muscle pain and headache. Some people infected with influenza A(H1N1) 2009 may also have nausea, vomiting and diarrhoea. Most cases of influenza A(H1N1) 2009 have been mild though fatal cases have been reported.


Mode of transmission

Similar to influenza due to other seasonal influenza strains, the infection is mainly spread through droplets and by direct contact with the secretions of infected persons.

Management

Persons with flu-like symptoms should take adequate rest and drink plenty of water. They should put on a mask if they develop respiratory symptoms. If symptoms persist, they should see a doctor.

Antiviral agents can reduce the severity and duration of illness but must be used under doctor's prescription. Antibiotics are unnecessary unless influenza is complicated by bacterial infection. It is important for people not to self-medicate.

Prevention

Influenza vaccination is one of the effective ways in preventing seasonal influenza and its complications. The recommended seasonal influenza vaccines used in 2010/11 contain Influenza A (H1N1) 2009-like viruses. Based on the Recommendations on Seasonal Influenza Vaccination for the 2010/11 Season given by the Scientific Committee on Vaccine Preventable Diseases of the Centre for Health Protection, high risk groups should get vaccinated.

In addition, members of the public should strictly maintain personal and environmental hygiene practices to prevent spread of the disease:

• Observe personal hygiene
• Keep hands clean and wash hands properly. Alcohol-based handrub is also effective when hands are not visibly soiled.
• Wash hands with liquid soap promptly if they are contaminated by respiratory tract secretions, e.g. after sneezing or coughing.
• Cover nose and mouth when sneezing or coughing.
• No spitting. Always wrap nasal and mouth discharges with tissue paper, and dispose of the tissue paper properly in a lidded rubbish bin.
• Wear mask when symptoms of respiratory tract infection or fever develop. Seek medical advice promptly.
• Refrain from work or school if develop symptoms of influenza.
• Observe environmental hygiene
• Maintain good ventilation of indoor areas.
• When influenza is prevalent, avoid attending crowded and poorly ventilated public places.