Influenza

INFLUENZA

Background Information
Influenza (or flu for short) is a common viral infection which affects everyone at one time or another. In the tropics , there is no clear cut flu season but in the temperate countries, it often peaks in the winter months, where flu epidemics occur consistently. There are 2 flu epidemic seasons annually, one which coincides with the winter in the Southern Hemisphere and another larger epidemic during the Northern Hemisphere winter months. In Singapore, we have a low level baseline flu activity with small peaks during the 2 epidemics which coincides with the Northern and Southern Hemisphere winter. This is thought to be due to travel patterns of Singaporeans and visitors to our country.

Epidemiology
In Singapore, we do not have a clear cut flu season but there is a low level baseline incidence of flu throughout the year with incidence peaking in the middle and end of the year coinciding with the Southern Hemisphere and the Northern Hemisphere winter epidemics respectively. The highest incidence seen at the end of the year can peak to 20,000 cases per week at our polyclinics.

Clinical
Influenza is caused by the influenza virus which is different from the “common cold” which is caused by Rhinovirus. It is a highly contagious airborne infection and can be transmitted by coughing, sneezing, saliva and close contact with the infected individual. Sometimes, it can be transmitted from contact with inanimate objects like door knobs, handrails, contaminated drinking glasses and surfaces. The main symptoms are:

  • Fever of sudden onset
  • Myalgia ( body aches ) and headache
  • Coughing
  • Sneezing
  • Running nose
  • Sorethroat

There are 2 main types of flu viruses, flu A and flu B, of which flu A is more likely to cause epidemics and more severe illness.

Other notable flu illnesses include bird flu and swine flu which affects animals and sometimes can mutate to adapt to human hosts.

The high risk groups for influenza infection are:

  • Those >65 years old
  • Those between 6 months to 5 years old
  • Pregnant
  • Those with chronic heart and lung problems
  • Those with chronic diseases like Diabetes, Renal failure, etc
  • Those who are immunocompromised eg. organ transplant, long term steroids, HIV infection, chronic aspirin therapy
Complications include:

  • Myocarditis
  • Pneumonitis/pneumonia
  • Encephalitis (Brain inflammation)
  • Death

Treatment
Treatment is with anti-viral drugs which must be started as soon as possible, preferably within the first 2 days. The 2 most common drugs used are Oseltamivir (Tamiflu) and Zanamivir (Relenza). Sometimes, we may have to give antibiotics for superimposed bacterial infections which commonly follow viral infections.
Note: Antiviral treatment must not be used as a substitute for flu vaccinations

Prevention
The best prevention for influenza is annual flu vaccination. Other prevention measures include the practice of hand hygiene as frequently as possible especially after visiting public places and healthcare facilities.

Points to Note
There are 2 new vaccines which are available annually with one set in March/April (for Southern Hemisphere (SH))and another in September/October (for Northern Hemisphere (NH)).

Do not worry about whether it is NH or SH vaccine because, we will administer the latest available vaccine.
The best time to vaccinate is before the end of the end around October.

Current vaccines protect against 2 flu A strains and one flu B strain. HINI is a component of all current flu vaccines.

Please note that bird flu strain, H7N9 is not covered in the regular flu vaccine.

There is a bird flu vaccine which is not available commercially and given to certain bird farmers and laboratory workers working with bird flu virus.

Please take your flu vaccine at least 2 weeks before the needed protection. Flu vaccination is updated yearly because there is often a new strain every season.

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