A pandemic is an infectious disease, such as influenza, which spreads from person to person over a wide area of the world. It may be mild or severe depending upon the symptoms caused by the infection. The World Health Organization has defined various stages in the development of a pandemic. Both the World Health Organization, WHO, and the Centers for Disease Control in the United States of America, CDC, monitor pandemics and provide planning guidelines which may be useful to individuals, families, and organizations.