Outbreak

An outbreak is an event that sometimes cannot be controlled for several months, years, or longer. The word "outbreak" is a term used in epidemiology. It describes what happens when a disease becomes widespread that first thought. An outbreak can affect a small group or affect thousands of people across the world. An outbreak can be epidemic.

 Types 
Common source - all victims got the disease from the same source (such as water pollution)Glossary of Epidemiology Terms, Cdc.gov (2007-04-25). Retrieved on 2010-11-25.
Continuous source - when the disease continues to spread for a longer time.
Point source - when the disease continues to spread for a short time.
Propagated - disease is spread from person to person.
Behavioral risk related - disease is spread by a person's behavior such as sexually transmitted diseases and malnutrition.
Zoonotic - disease is spread from animal to animal.
Patterns of an outbreak
Endemic - a common disease such as influenza, measles, mumps, pneumonia, colds and smallpox. This is characterized by a place, group or activity. 
Epidemic - when the disease affect a large group of people.
Pandemic - when the disease affects people worldwide.

 References 

Category:Epidemiology