Clinical Course

The clinical course describes the evolution of a disease. A disease can have an acute, subacute, or chronic course. An acute disorder is one that is relatively severe, but self-limiting. Chronic disease implies a continuous, long-term process. A chronic disease can run a continuous course, or it can present with exacerbations (aggravation of symp­toms and severity of the disease) and remissions (a period during which there is a lessening of severity and a de­crease in symptoms). Subacute disease is intermediate or between acute and chronic: it is not as severe as an acute disease and not as prolonged as a chronic disease.

The spectrum of disease severity for infectious diseases such as hepatitis B can range from preclinical to persistent chronic infection. During the preclinical stage, the disease is not clinically evident but is destined to progress to clin­ical disease. As with hepatitis B, it is possible to transmit the virus during the preclinical stage. Subclinical disease is not clinically apparent and is not destined to become clin­ically apparent. It is diagnosed with antibody or culture tests. Most cases of tuberculosis are not clinically apparent, and evidence of their presence is established by skin tests.

Clinical disease is manifested by signs and symptoms. A persistent chronic infectious disease persists for years, some­times for life. Carrier status refers to an individual who har­bors an organism but is not infected, as evidenced by antibody response or clinical manifestations. This person still can infect others. Carrier status may be of limited du­ration, or it may be chronic, lasting for months or years.

In summary, health is determined by many factors, including genetics, age and sex, and cultural and ethnic differences. The WHO defines health as a ^“state of complete physical, mental, and social well-being and not merely the absence of disease and infirmity."

The ability of the body to adapt to changes that occur in both health and disease is affected by such factors as age, health status, and psychosocial resources. Adaptation is fur­ther affected by the availability and number of adaptive re­sponses. Extreme age and disease conditions, such as when changes occur suddenly rather than gradually, also affect the capacity to adapt.

The term pathophysiology may be defined as the physiology of altered health. A disease has been defined as any deviation from or interruption of the normal structure or function of any part, organ, or system of the body that is manifested by a char­acteristic set of symptoms or signs and whose etiology, pathol­ogy, and prognosis may be known or unknown. The causes of disease are known as etiologicfactors. Recognized etiologic agents include biologic agents (bacteria, viruses), physical forces (trauma, burns, radiation), chemical agents (poisons, alcohol), and nutritional excesses or deficits. Pathogenesis describes how the disease process evolves. Morphology refers to the structure or form of cells or tissues; morphologic changes are changes in structure or form that are characteristic of a disease.

Disease can manifest itself through signs and symptoms. A symptom is a subjective complaint, such as pain or dizziness; a sign is an observable manifestation, such as an elevated temperature or a reddened sore throat. A syndrome is a com­pilation of signs and symptoms that are characteristic of a spe­cific disease state.

The clinical course of a disease describes its evolution. It can be acute (relatively severe, but self-limiting), chronic (con­tinuous or episodic, but taking place over a long period), or subacute (not as severe as acute or as prolonged as chronic). Within the disease spectrum, a disease can be designated pre-clinical, or not clinically evident; subclinical, not clinically ap­parent and not destined to become clinically apparent; or clinical, characterized by signs and symptoms.