In the Event of Disease

When disease occurs, it is important to know the number of new cases (called incidence), characteristics of those with the disease (distribution/person), where the cases occurred (distribution/place), and whether the cases were scattered over time or occurred within a short period (distribution/time). This information is used to investigate the cause and source of disease. It can also be used to prevent additional illness and control the disease.

Information on number of cases by person, place, and time becomes extremely important in describing and addressing a public health problem. Epidemiologists, or Disease Detectives, use data collection or surveillance systems to identify patterns in disease occurrence. These patterns are used to determine the expected level of various health conditions or diseases across the United States or world. These systems can then be used to identify when levels of a disease are greater than expected and may require further investigation.

Sporadic illnesses are uncommon and occur irregularly. Some diseases are constantly present or endemic in a particular population. When a disease level remains constantly higher over time and affects all or most age groups, the condition can be considered hyperendemic.

Occasionally, the level of a disease in an area is clearly greater than expected for that condition. This is referred to as an epidemic. Within a limited geographic area, it can also be called an outbreak. When the number of cases are spread over several countries or continents, it can be called a pandemic.

In some cases, aggregations of rare of unusual diseases are identified that are perceived as being excessive. However, the expected amount of disease is not known. These instances are often referred to as clusters. These are often associated with cancers and other chronic conditions.

The amount of disease in a community is dynamic. Over time, expected levels of disease may change. Monitoring these trends can help epidemiologists plan control and prevention measures for future occurrences of disease. This can result in reduced numbers of cases and, over time, lower expected levels of disease.