Flu Epidemics

Seasonal flu epidemics usually begin suddenly and occur mainly in the late fall and winter. In the northern hemisphere, the typical flu season occurs from October to April. Flu epidemics can spread rapidly through communities and even across vast geographic distance. Worldwide influenza epidemics (pandemic) have occurred several times in the last century.

The most recent influenza pandemic occurred in 2009. A study of the 2009 H1N1 pandemic, co-authored by 9 members of the CDC Influenza Division, estimated the worldwide influenza related death toll to be between 151,700 and 575,400. About 80% of the "deaths were in people younger than 65 years of age which differs from typical seasonal influenza epidemics during which 80-90% of deaths are estimated to occur in people 65 years of age and older." Researchers found that the shift in the age distribution of influenza deaths to younger age groups resulted in 3 times as many years of life lost than would have occurred for the same number of deaths during a typical influenza season. "A disproportionate number of deaths occurred in Southeast Asia and Africa, where access to prevention and treatment resources are more likely to be limited."

The virulence of influenza epidemics and pandemics vary. The previous H1N1 influenza pandemic occurred in 1918. It took the lives of 500,000 Americans and at least 20 million people worldwide. In Pennsylvania, during one month, over 100,000 deaths occurred. In San Francisco, during the same outbreak, 78% of hospital nurses fell ill with influenza. While medical care is vastly improved since 1918, another virulent pandemic is highly likely if not inevitable. Health care professionals need to be prepared.

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A single flu epidemic could spread throughout the entire world.