An outbreak of a serious contagious disease that spreads rapidly and widely within a specific city, region or country. Epidemics generally exceed expectations of the severity and prevalence of a disease. An epidemic that is widespread over multiple regions worldwide is known as a pandemic.
Widespread epidemics experienced in Australia include the bubonic plague, H1N1, Poliomyelitis and Spanish Influenza. Many of these diseases have been controlled through the increased use of vaccines.
Image: The H1N1 virus under a microscope, Centre for Disease Control Influenza Laboratory