Key Terms
Disease
Any condition in which the normal structure or function of the body is damaged or impaired.
Infection
Successful colonization of a host by a microorganism.
Signs
Objective, measurable, clinically observable.
Symptoms
Subjective, felt by the patient, cannot be clinically confirmed.
Syndrome
A specific group of signs and symptoms characteristic of a particular disease.
Infectious disease
Caused by direct effect of a pathogen (cellular: bacteria, parasites, fungi; acellular: viruses, viroids, prions).
Communicable disease
Capable of being spread person to person, directly or indirectly.
Contagious disease
Easily spread person to person. All contagious diseases are communicable; not all communicable diseases are contagious.
Noncommunicable infectious disease
Not spread person to person; contracted via environment or animals.
Iatrogenic disease
Contracted as a result of a medical procedure (wound treatment, catheterization, surgery).
Nosocomial disease
Disease acquired in a hospital setting.
Zoonotic disease (zoonosis)
Transmitted from vertebrate animal (sometimes defined as any animal) to humans.
Morbidity
Number of cases of a disease. Mortality: number of deaths due to a disease.
Asymptomatic/subclinical disease
No noticeable signs or symptoms.
Acute disease
Pathologic changes over a short time (hours, days, weeks); rapid onset.