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Influenza

What is influenza?

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  • Influenza is caused by a virus that attacks mainly the upper respiratory tract – the nose, throat and bronchi and rarely also the lungs

  • Hospitalization and deaths mainly occur in high-risk groups (elderly, chronically ill)

  • More prevalent in January-March and July-August each year in HK

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Type of influenza

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Three types of influenza viruses are recognized: A, B and C

The currently circulating influenza viruses that cause human disease are type A and B

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Type A

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  • Influenza A has 2 subtypes which are important for humans: A(H3N2) and A(H1N1), of which the former associated with most death.

  • It is infectious to mammals e.g. pig, birds and human

  • Emergence of new subtypes occurs from time to time at irregular intervals

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Type B

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  • Also common in HK and is infectious to human only

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Type C

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  • Less commonly seen in HK

  • Can be epidemic 

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Causes - How is influenza transmitted?

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  • Via air droplets

  • Small particles from cough and sneeze

  • The influenza virus enters the body through the nose or throat

  • Disease spreads very quickly among the population especially in crowded circumstances

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Clinical symptoms

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  • Incubation period around 1 to 3 days

  • Three main symptoms, namely fever, sore throat and cough

  • Headache, muscle pain, runny nose and other symptoms like tiredness, diarrhea and vomiting may also appear

  • Usually self-limiting with recovery in 2 to 7 days

 

Difference between influenza and common cold

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Managing influenza

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  • Infected persons should take adequate rest and drink plenty of water

  • Antiviral agents can reduce the severity and duration of illness e.g. amantadine is effective for strains of influenza A    

  • Antibiotics are unnecessary unless influenza is complicated by bacterial infection

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Prevention of Influenza

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  • Maintain good personal and environmental hygiene.

  • Build up body resistance by balanced diet and regular exercise

  • Avoid crowded environment during flu season

  • Vaccination - Recommended to receive each year to maintain the protection

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Who should not receive the vaccine?

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  • Individuals with egg protein or vaccine components allergies

  • With fever or infection on day of vaccination

  • Infants under 6 months old

Useful Links:

The Family Planning Association of Hong Kong

Smoking Cessation Programme

United Christian Nethersole Community Health Service 

Centre for Health Protection Hong Kong  

Hospital Authority

Race Relations Unit

 2344 3019

5622 1771

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