Glossary

Glossary of Terms:  I have realized that given the diverse backgrounds of my readers, there is a risk that jargon may be a barrier to reading my blog. Hence, this glossary. This will be updated as needed with future posts.

Airborne Transmission. Transmission where the pathogen is suspended in the air on droplet nuclei (residue from evaporated droplets) or dust particles. The pathogen is resistant to desiccation (drying) and can remain suspended in the air for prolonged periods of time. In the healthcare setting, to prevent this form of transmission, patients are isolated in negative pressure rooms, providers and staff use N95 masks or positive air pressure respirators, and healthcare staff are vaccinated (when possible and necessary). Only a few diseases are transmitted via this route: Measles, Chickenpox, Tuberculosis.

Basic Reproduction Number (R0). The number of new cases originating from a single infectious individual when a disease appears in a nonimmune population.

Competence (Vector Competence). The mechanical or biological ability of a vector to transmit a pathogen to a host.

Conservation Medicine. An emerging, transdisciplinary field that studies the relationship between human, animal, and environmental health. Essentially synonymous with One Health, though this term is more often used by wildlife biologists and ecologists.

Contact Transmission. Transmission of a pathogen by physical contact between the infected person and a susceptible person. In hospital settings, patients are placed in contact isolation (where providers where a gown and gloves) to avoid transmission of highly drug resistant pathogens like methicillin resistant Staphylococcus aureus (MRSA), vancomycin resistant Enterococcus (VRE), carbapenem resistant Enterobacteriaceae (CRE), for example.  Clostridium difficile infected patients are usually placed in contact isolation with additional special precautions, namely handwashing is required (rather than using alcohol foam) and instruments need to be cleaned with bleach wipes. Some diseases are though to require close contact to allow transmission (such as leprosy), where transmission is seen within family units but not with contact in the healthcare setting.

Droplet Transmission. Transmission via droplets, usually expelled with coughing, sneezing, or talking. Medical procedures such as bronchoscopy can produce droplets as well. These particles are much larger than the droplet nuclei that allow airborne transmission. Because of their large size, they do not stay suspended in the air for more than 3 feet. Droplet transmission is prevented by wearing a surgical mask, sometimes with eye protection. (The latter described as modified droplet isolation.) Coronaviruses, such as SARS and MERS, are transmitted by this route.

Elimination of a Disease. Reduction of the incidence of an infectious disease to zero in a defined geographic area. (Eg, “Measles was eliminated from the United States in 2000, but due to poor vaccine adherence reemerged.”) In 1998, Dowdle proposed definitions of disease control, elimination and eradication. (Dowdle WR. The principles of disease elimination and eradication. Bull World Health Organ 1998;76 Suppl 2:23-5.)

Epidemiology. Field of medical science that deals with the description, determinants, and potential control of diseases and conditions impacting health.

Epidemic. The widespread occurrence of an infectious disease in a population over a specific period of time above baseline incidence of the disease. A disease having these attributes.

Epizootic. Epidemic disease in an animal population. (See Epidemic.)

Endemic. A disease regularly found in a population. A disease having these attributes.

Enzootic. Endemic disease in an animal population. (See Endemic.)

Eradication of a Disease. Permanent reduction of the incidence of an infectious disease to zero worldwide. (Eg, “Only one human disease, smallpox, and one animal disease, rinderpest, have been eradicated.”) In 1998, Dowdle proposed definitions of disease control, elimination and eradication. (Dowdle WR. The principles of disease elimination and eradication. Bull World Health Organ 1998;76 Suppl 2:23-5.)

Fecal-Oral Transmission. Transmission of a pathogen found in feces that then enters the mouth. Fecal-oral transmission can occur with ingestion of inadequately treated sewage contaminated water for example.

Immunology. Field of medical science that deals with aspects of the immune system.

Indirect Contact Transmission. Transmission of a pathogen via contaminated physical objects (fomites). In the healthcare setting, this can include bedding, handrails, doorknobs, curtains, and medical instruments for example.

Isolation. The separation of colonized or ill patients from people who are not colonized or ill. This is in contrast to Quarantine (see below). For example: (1) Patients colonized with MRSA (methicillin resistant Staphylococcus aureus are typically placed in contact isolation to avoid transmission of the resistant bacteria to other patients. (2) Patients infected with measles are placed in airborne isolation to prevent transmission of the contagious disease to others who may not be immune. As an editorial note, the media frequently confuses the two terms, Isolation and Quarantine.

N95 Respirator. Respiratory mask that filters at least 95% of airborne particles. These are regulated by the Food and Drug Administration. N95 respirators are worn by health care workers caring for a patient in isolation for diseases that are transmitted via the airborne route.

Negative Pressure Room. A room used to isolate patients infected with pathogens that are transmitted via the airborne route. The room has a ventilation system that forces air into the room and out through filters which ‘capture’ infectious particles suspended in the air. Patients typically placed in a negative pressure room include those with contagious chickenpox, measles, or pulmonary tuberculosis.

One Health. The transdisciplinary collaboration to attain optimal health for people, animals and the environment. As noted on the CDC website, “the One Health concept recognizes that the health of humans is connected to the health of animals and the environment.” Essentially synonymous with Conservation Medicine, though this term is more often used by veterinarians.

PAPR. See Powered Air Purifying Respirator.

Pathogenicity. Ability of an organism to cause disease.

Powered Air Purifying Respirator (PAPR). An air-purifying respirator that uses a blower to force ambient air through an air-purifying filter element into a hood worn over the head. A PAPR may be worn by a healthcare provider instead of an N95 mask when caring for a patient in airborne isolation.

Quarantine. The separation and restriction of movement of people who are not ill, but who have exposed to a contagious disease to see if they become ill. This is in contrast to Isolation (see above.) As an editorial note, the media frequently confuses the two terms, Isolation and Quarantine.

R0. See Basic Reproduction Number.

Reservoir. Source of infection of a pathogen when it is not infecting its host. The reservoir may be environmental (for example: Highly nitrogen rich soil is the environmental reservoir of the fungal pathogen Histoplasma capsulatum.) or may be an alternate host (See Reservoir Host below.)

Reservoir Host. Host of an infectious disease that serves as an ongoing source of infection and reinfection to non-reservoir hosts (alternate or inadvertent hosts). For example, bats serve as a major reservoir host for rabies.

Serology. Though this can refer to the field of medical science that deals with serum and serum proteins, I think that is rather archaic. In more modern use, this usually refers to the identification and/ or quantitation of antibodies (usually to infectious agents).

Sexual Transmission. Transmission of a pathogen via sexual contact.

Trophic Level. Ecological term defining the position an organism occupies in a food chain. To be crude, what it eats and what eats it. Example trophic levels include: primary producer (such as grass), primary consumer (herbivores such as bison), secondary consumers (such as wolves), and tertiary consumers (scavengers and decomposers that ultimately feed off the carcass of the dead wolf).

Vector. Any agent (though usually this is an insect) that carries and transmits a pathogen to a host.

Vector-borne Disease. Disease caused by a pathogen which is transmitted by insect bite.

Virology. Field of science studying viruses.

Virulence (Virulence Factors). Virulence is the extent of pathology caused by the organism, usually correlating to the organism’s ability to multiply in the host. Virulence factors are pathogen derived molecules that contribute to the organism’s pathogenicity. Virulence factors may aid the pathogen in colonization, invasion, immunoevasion, cell entry, metabolic success, or tissue injury.

Virus. A small infectious agent that is capable of replication only inside the living cells of a host species.

Zoonoses. Infectious diseases of humans acquired from vertebrate animals.

Zoonotic. Pertaining to a zoonosis.