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Glossary Terms

Glossary of Terms

  • Immune globulin is an injection of purified, highly concentrated antibodies from other people who have successfully fought a particular disease, and is typically given to prevent infection until that person can either produce their own antibodies or the vaccine takes effect.
  • Incubation period is the length of time between when a person is first infected with a pathogen to when they begin to show symptoms.
  • Infection occurs when a pathogen grows in or on a host and causes an immune response (i.e., the creation of antibodies).
  • Colonization occurs when a pathogen grows in or on a host but doesn't cause an immune response (i.e., the creation of antibodies).
  • Endemic A disease is considered to be endemic in a defined area when it is at a constant, low rate of transmission.
  • Epidemic An epidemic (also referred to as an outbreak) is a spike in the rate of disease for a particular area.
  • Pandemic A pandemic refers to a worldwide epidemic.
  • Vaccines create immunity in a vaccinated person by exposing them to the portions of the pathogens that create antibodies, while the vaccine itself does not cause disease. After a full course of vaccines, a person is said to be protected against that particular disease. There are several types of vaccines, including:
  • Killed vaccines, which consist of the actual pathogen that has been killed or inactivated by high temperature or certain chemicals. Because they still look like the live pathogen to the body, it creates antibodies against the disease.
  • Live, attenuated vaccines are made by growing the pathogen in unusual hosts so that it acquires mutations and becomes less infectious. It can then be used in a vaccine because it is still capable of causing infection, but not disease since, in comparison, the body is better at making antibodies. The person is then protected against wild-type (non-attenuated) disease since they both look the same to the body.
  • Acellular vaccines involve injecting just the proteins of the pathogen that are recognized by the body in the creation of antibodies. Because of this, there is no chance of even mild disease from the vaccine; however, due to the complexity of the immune response, the immunity created by such vaccines is not always as complete as either the killed or attenuated vaccines.
  • Polysaccharide and conjugate vaccines create an immune response for those bacteria that are surrounded by a polysaccharide (carbohydrate) shell. Since carbohydrates generate a weaker immune response than proteins, they can be conjugated (attached) to antibody-generating proteins to create a stronger response.
  • Close Contact, according to the CDC, means having cared for someone with the illness, or having direct contact with respiratory secretions and other body fluids. Examples of close contact include kissing or hugging, sharing eating or drinking utensils, talking to someone within 3 feet, and touching someone directly. Close contact does not include activities like walking by a person or briefly sitting across a waiting room or office.
  • Isolation is the separation of ill patients with a communicable disease from the healthy population. While this is usually done in a hospital setting, it can occur at home.
  • Quarantine is the separation of healthy persons exposed to an infectious agent from the general population. This may involve a simple curtailment of activities, to being asked to remain completely in the home or shelter until the incubation period of the disease has passed. A quarantine is typically performed on a voluntary basis.
  • A vector is an organism (as an insect) that transmits a disease causing agent  from one organism or source to another.

What Is Epidemiology?

Epidemiology: 1: A branch of medical science that deals with the incidence, distribution, and control of disease in a population; 2: The sum of the factors controlling the presence or absence of a disease or pathogen. (From Merriam-Webster's Collegiate Dictionary, Tenth Edition, Merriam-Webster, Incorporated, 1999.)

Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems. (From: Last, JM: A Dictionary of Epidemiology, Fourth Edition, Oxford University Press, 2001.)

  • Prophylaxis is the use of medication, usually antibiotics or antivirals, to prevent disease before it occurs in an exposed person. Examples of prophylaxis include rabies and varicella vaccines, and the use of antibiotics among close contacts of pertussis cases.
  • Systemic refers to a disease that involves the whole body, not just one part or organ system. Many times, "systemic" refers to a rash that covers the entire body.
  • Surveillance is defined as the collection, analysis, and interpretation of data in order to control and prevent disease.
  • Asymptomatic infections occur when a person is infected with a particular pathogen, they create an immune response, but do not show symptoms of the disease.
  • Reservoir refers to the particular animal species where a pathogen is permanently maintained in nature and where it lives in between outbreaks.
  • Sepsis generally refers to a bacterial infection of the bloodstream, and these tend to be very serious infections with very high mortality rates. Often, the bacteria travel to the bloodstream from an infection in another part of the body.
  • Mortality rate is the percentage of people with a particular disease who die as a direct result of that disease. A high mortality rate means that many people died because of that disease, such as in Ebola hemorrhagic fever.
  • Contagious means that a person is infected with a particular disease and is capable of passing it on to another person whether or not they have symptoms
  • A carrier of a bacterium or virus is colonized by the pathogen but does not demonstrate symptoms of infection nor an immune response
  • Prophylaxis is treatment with medications to prevent a disease, usually in persons exposed to the pathogen that causes it
  • Pre-exposure prophylaxis is when a person takes the medication before a time when they know they will be exposed to a certain pathogen
  • Post-exposure prophylaxis is when a person takes the medication after they have been exposed to a pathogen in order to prevent the development of symptoms and disease


The immune system is the way our body fights off infections from all types of pathogens. It does this by differentiating between cells that belong to our own bodies ("self") and all other types of cells ("non-self"). If the immune system finds something non-self, then it will try to kill the non-self cell.


In order to kill a non-self object, the immune system will operate in one of two ways:

  • Non-specific immunity, in which the immune system uses mechanisms which will kill a wide variety of cells and pathogens. Non-specific mechanisms include creating a harsh environment on the skin surface, creating general chemicals that kill viruses and bacteria, and by bursting open bacteria
  • Specific immunity, where the immune system responds against one particular non-self object by creating antibodies (proteins that recognize other proteins on foreign particles), which call in the cells of the immune system, B cells and T cells. B and T cells fight back against pathogens which have invaded the body's own cells by killing the infected cells.

How do vaccines work?

Vaccines work by creating specific immunity to a particular pathogen. The first time the body "sees" a foreign protein on a pathogen, several days pass before enough antibodies and B and T cells have been created to successfully kill the pathogen. During this time, you feel sick. However, with some pathogens, the second or third time your body "sees" a pathogen, your body remembers the pathogen and uses the antibodies and B and T cells it has saved to fight off the pathogen right away, before you have a chance to feel sick.

A vaccine makes the body think it has seen a particular pathogen and allows it to create and store the pathogen-fighting antibodies and B and T cells so that a person won't get sick if they become infected with the real pathogen.