An endemic refers to the usual presence of a disease within a geographic area, such as chickenpox among children in the US. An epidemic is when an infectious disease spreads rapidly to many people in excess of normal rates, like SARS in 2003. A pandemic is a global epidemic, such as HIV/AIDS or influenza that has occurred throughout history. Prevention methods include vaccinations, hand washing, and avoiding mosquito bites to prevent the spread of diseases from endemic to epidemic or pandemic levels.