Infectious diseases are caused by pathogenic agents that enter the body, such as bacteria, viruses, fungi, and animal parasites, where they grow and multiply to create symptoms that can range from mild to fatal. Examples of infections include measles, yellow fever, the common cold, tuberculosis, mumps, hepatitis, influenza, the coronavirus, and so forth. The sites of infection include the lungs, eyes, ears, and urinary and digestive tracts, among others. The CDC defines communicable disease as “an illness caused by an infectious agent or its toxins that occurs through direct or indirect transmission” (http://www.cdc.gov/tb/programs/laws/menu/definitions.htm). Prevention of infection includes actions by patients, physicians, nurses, and public health professionals that are aimed at ensuring safety and reducing the likelihood of microbial invasion and multiplication as well as decreasing the chance for transmission to others. Toxins from food poisoning or infection caused by toxins in the environment, such as tetanus, are examples of noncommunicable diseases.

The term standard precautions refers to a system designed to reduce the risk of transmission of microorganisms from both recognized (e.g., environment) and unrecognized sources of infections. Standard precautions direct safe practices and are designed to protect healthcare workers, patients, and others from exposure to bloodborne pathogens or other potentially infectious materials from any body fluid or unfixed human tissue from any person, living or dead. The term universal precautions was replaced in 1996 with the term standard precautions.

Guidelines are based on information about infectious disease patterns, modes of transmission (e.g., skin contact, inhalation, ingestion, insect bites), and safe practice interventions. The guidelines are designed to be user friendly, to control nosocomial infections, and to reduce the risk for transmission of both known and suspected infections and include airborne, droplet, and contact precautions to prevent the spread of known or suspected transmissible and virulent pathogens. Isolation and quarantine may be needed to stop the spread of disease.