History

• Several influenza pandemics were recorded in the 20th century. The Great Influenza Pandemic of 1918-1919 was clearly the worst, causing 20 to 40 percent of the world population to fall ill and resulting in the deaths of 50 million people. Smaller outbreaks were recorded in various parts of the world, particularly in the Far East. Two versions of the flu virus, H1N1 (Swine Flu) and H5N1 (Bird or Avian Flu) remain serious threats in 2010.
  
  

Types

• There are three basic types of influenza viruses, labeled A, B and C. A and B viruses are primarily responsible for seasonal influenza, and C mainly causes minor respiratory distress and is not responsible for major epidemics. Influenza A viruses are also found in many animals, including horses and seals.
  
  

Symptoms

• Flu symptoms include fever, muscle ache, fatigue, sore throat and runny nose, and children in particular may experience vomiting and diarrhea. Most people recover within two weeks, but these symptoms can sometimes result in more serious issues such as pneumonia. Older people, pregnant women and children are more at risk of complications from influenza.
  
  

Geography

• The CDC maintains surveillance of reported cases of influenza and publishes a weekly report of the geographic spread of reports in the United States. During the 2009-2010 influenza season, coastal regions were hit hardest, in particular California and Florida, although the United States as a whole reported widespread rates of infection.
  
  

Prevention/Solution

• Seasonal vaccination against influenza viruses plays a key role in holding back the spread of this infectious disease.