The flu, also known as the common or winter flu, is a contagious illness that affects an individual’s breathing functions. Flu outbreaks occur each year, usually in winter, in moderate climates. Every year in the United States, 5 percent to 20 percent of the population gets the flu. More than 200,000 people in the United States are hospitalized each year from flu complications, such as pneumonia and dehydration; about 36,000 people die from flu annually.


Flu symptoms include fever, cough, runny nose and muscle aches. Flu-related complications, such as pneumonia, may cause death. Healthy adults are usually not at risk for serious complications; however, very young children, the elderly and those with certain underlying health conditions may be more at risk.


Flu viruses are spread in droplets caused by coughing and sneezing. This can happen when the droplets from an infected person’s cough or sneeze fall in the mouths or noses of people nearby or if a person touches something infected with flu viruses, such as doorknobs and sinks. The yearly flu vaccine is the best way to prevent the flu. There are two types of vaccines:

  • Flu shot, an inactivated vaccine (contains dead virus) that is given with a needle;
  • Nasal-spray flu vaccine, a vaccine made with live, weakened flu viruses

Practicing basic hygiene, such as regular hand washing and covering the mouth when sneezing or coughing, can also help prevent the flu’s spread.


There are three types of flu virus: A, B and C. The Type A virus includes 16 subtypes of which only two (H1 and H3) are associated with widespread epidemics, according to the Control of Communicable Diseases Manual (CCDM), published by the American Public Health Association. Epidemics are defined as diseases that suddenly occur in communities, regions or countries in unusually high numbers. The Type B virus is infrequently associated with regional or widespread epidemics; Type C with occasional outbreaks and minor confined outbreaks.

During the initial phase of epidemics in industrialized countries, infection and illness appear mainly in school-age children, with a sharp rise in school absences, doctor visits and children’s hospital admissions, according to CCDM. Most epidemics usually last three to six weeks.

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