Influenza

• The influenza virus is subject to many mutations as it reproduces and goes from host to host. These mutations give it increased resistance against the body's immune systems and against antiviral medication. The 2009 H1N1 influenza virus is a mutant variant of the seasonal influenza strain.
  
  

Influenza-like Illness

• Because it is impossible to test each and every single person that arrives at a physician's office or hospital complaining of the flu, a syndrome known as "influenza-like illness" or ILI is used as a proxy to measure the burden of the flu on the population.
  
  

2009 H1N1 vs. Seasonal Flu

• According to the Centers for Disease Control and Prevention (CDC), the proportion of people visiting physicians' offices and hospitals with ILI is not larger at the peak of H1N1 2009 influenza activity than during seasonal influenza activity.
  
  

Symptoms

• With only a few anecdotal reports of gastrointestinal symptoms, the symptoms of the 2009 H1N1 flu are no different than those of the seasonal strain. These include fever, malaise, sore throat, cough, and nausea.
  
  

Complications

• Like with seasonal influenza, certain groups of people with underlying medical conditions are more at risk for developing complications from either the 2009 H1N1 influenza strain or the seasonal influenza strain. All people with underlying medical conditions or who have been shown to be more at risk of complications are strongly encouraged by CDC and other public health authorities to get vaccinated.