A disease is said to be an epidemic or an epidemic disease when new cases of that disease, in a certain population and during a given period, occur much more frequently than is expected based on the current incidence rate. An incidence rate is the average number of new cases of a disease that occur during a specified time. So, for example, if more people than usual begin to be diagnosed with diabetes in the United States, then diabetes would be said to be an epidemic. In order to be considered an epidemic, a disease does not have to be communicable.

Today, cancer and heart disease are considered to be of the epidemic kind within the United States. A famous historical example would be the Black Plague. Factors that may attribute to the start of a new epidemic may include sudden changes in agricultural practices, sudden changes in society or demographics, general poor health amongst a particular population, evolution of the offending disease or illness, a lack of adequate treatment for those diseases or sicknesses, contamination of a population’s food sources or water supply, international travel that causes one to be exposed to new diseases, failure of the public health programs, international trade, sudden and unexpected changes in climate, reduced levels of biodiversity, and poor urban planning.

There is a difference between pandemic epidemic outbreaks, though the two are quite often confused. Pandemics are epidemics of infectious diseases, but on a much larger scale than that of an epidemic. Pandemic diseases are any diseases that have spread through a large region, such as a continent, or they may even be so serious as to be worldwide. Swine flu, seasonal flu, and HIV, for example, are all pandemic outbreaks. Famous pandemics of the past include Smallpox and Tuberculosis. In short, a virus epidemic is localized, while a virus pandemic can spread outwardly. Often times, scientists, doctors, and researchers are able to get a virus pandemic or virus epidemic under control. For example, within four years of AIDS becoming an epidemic, scientists had identified the virus, HIV, that caused AIDS, figured out how it was being transmitted, and developed a blood test to detect infection. In the past, this process took much longer. Polio, for example, was a problem lasting from the 1930s to 1954.

In short, it is important to understand the difference between epidemic and pandemic diseases. Epidemics occur on a local level, and gradually spread outward. Once the disease has spread to a much larger area and is no longer concentrated in one state, town, or country, it is considered to be pandemic. There are, fortunately, vaccinations and other types of treatments for most pandemic epidemic outbreaks today; and usually, if there are not, scientists and researchers are able to develop them relatively quickly. Contracting an epidemic disease does not necessarily mean the end of life in this day and time.