Influenza, also known as the flu, is a contagious disease that is caused by the influenza virus. It attacks the respiratory tract in humans (nose, throat, and lungs). The flu is different from a cold. Influenza usually comes on suddenly and may include these symptoms: fever, headache, tiredness (can be extreme), dry cough, sore throat, nasal congestion and body aches. These symptoms are usually referred to as "flu-like symptoms."
Influenza A viruses periodically cause worldwide epidemics, or pandemics, with high rates of illness and death. Unlike other public welfare emergencies, an influenza pandemic will impact on multiple communities across the United States and require swift and coordinated action and cooperation by all levels of government. Advanced planning for a large scale and widespread health emergency is required to optimize health care delivery during a pandemic. In addition, prevention and preparedness activities facilitate the response and recovery during and after an influenza pandemic.
Key Differences Between Seasonal and Pandemic Influenza
Occurs every year during the winter months.
Can occur in any season; historically occurs three to four times a century.
Affects 5-20 percent of the U.S. population.
Experts predict an infection rate of 25-50 percent of the population, depending on the severity of the virus
Annually kills between 500,000 and 1 million people worldwide including 36,000-40,000 in the U.S.
The "Spanish Flu" of 1918 killed 500,000 in the U.S. and 50 million worldwide.
Most people recover within one or two weeks.
Usually associated with a higher severity of illness and a higher risk of death.
Deaths generally confined to "at risk" groups:
All age groups may be at risk for infection, not just "at risk" groups:
The National Institute of Allergy and Infectious Diseases explains the emergence and potential spread of new influenza viruses.