Epidemiology & Biostatistics

The spectrum of disease describes the severity of disease. Severity can range from mild to severe. The natural history of disease refers to how a disease develops and progresses over time without intervention. Understanding the progression of disease is essential for prevention. Understanding how diseases develop and progress is also important to developing the best approaches for screening and diagnosing the disease.

Disease progression occurs in 4 stages:

1. Stage of susceptibility:  During this stage, the individual does not have the disease but is susceptible to the disease.
2. Stage of preclinical disease:  During this stage, the disease process has started but the person does not have symptoms of the disease. The disease may be detected by screening tests. This stage is also known as the presymptomatic stage, subclinical stage, or latent disease stage.
3. Stage of clinical disease:  During this stage, the individual experiences signs and symptoms of the disease and the disease is clinically apparent. Most diseases are diagnosed during this stage.
4. Stage of recovery, disability, or death:  During this final stage, the person recovers or dies from the disease. If the person recovers, s/he may or may not experience short- and long-term sequelae of the disease.

Preventative factors are of great interest to healthcare professionals. We know that we cannot protect our patients from all exposures and that we may not be able to change some biologic risk factors such as a person’s genetics. But, we may be able to mitigate the effects of some harmful exposures by preventative actions. Thus, healthcare professionals seek to understand the web of causation so that they can identify areas where preventative actions may stop the onset of disease or mediate the long-term sequelae of an existing disease process.

The focus of prevention is on preventing disease and its complications. There are three levels of prevention:

1. Primary prevention is focused on preventing the occurrence of disease. Primary prevention interventions are focused on the stage of susceptibility, before the disease process begins. In other words, primary prevention is focused on preventing the occurrence of disease. Examples of primary prevention include ensuring the availability of clean water and safe food, sanitation, immunizations, and hand cleaning. Primary prevention is used in the stage of susceptibility.
2. Secondary prevention is focused on identifying individuals in the stage of preclinical or early clinical disease, and intervening to minimize the impact of the disease. Secondary prevention interventions are focused on the early detection and treatment of the disease process to prevent progression of the disease process. The use of screening tests to identify people likely to have a disease is an example of secondary prevention. Screening focuses on the detection of unrecognized disease so that treatment can be implemented early in the disease process. Secondary prevention also includes the early treatment of disease to prevent its progression. Secondary prevention is used in the stage of preclinical (presymptomatic, subclinical, or latent) stage of disease.
3. Tertiary prevention is focused on minimizing the long-term impact of disease and helping the person achieve the highest level of function and quality of life as possible. Tertiary interventions are focused on recovery and rehabilitation after a disease or injury has occurred to achieve maximum function and well-being. Tertiary prevention is used during the last part of the stage of clinical disease and throughout the stage of recovery, disability, or death.