The worst epidemic was in 1918-1919 when over 500,000 people died in the United States and twenty million people died worldwide. Deaths are usually caused by complications of the flu, such as pneumonia. Healthy individuals rarely die of the flu, but they may be fairly miserable for up to a week or so. Usually, about 10,000 people die every year from complications of the flu. Flu epidemics usually occur from December through February, but several years ago it started in September.
Influenza accounts for millions of days lost from work each year.
Etiology Influenza A is caused by a virus that is able to change slightly from year to year so that a new vaccine has to be given every year to maintain protection. Viruses are very small germs that are much smaller than bacteria. Viruses are responsible for the bulk of colds and other childhood illnesses. Influenza B is also responsible for a flu-like illness, but it is not as severe as the Influenza A strain. The symptoms of Influenza A are fairly typical and initially consist of fever, muscle aches, headache, malaise and a dry cough.