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Acute Disease
a disease that develops rapidly and runs its course quickly; examples are measles and the common cold.
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Analytical Study
an epidemiological study that focuses on establishing a cause-and-effect relationship in the occurrence of diseases in populations; done after the occurrence of the outbreak has been fully described, done to identify specific factors, the risk factors, that result in high frequencies of disease.
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Attack Rate
the number of cases developing the infection per 100 people exposed.
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Bacteremia
an infection in which bacteria are transported in the blood but do not multiply in transit; often occurs in cases of injury such as a cut, abrasion, or teeth cleaning.
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Carriers
organisms that can harbor an infectious agent without having any observable clinical signs or symptoms, but can transmit the infection to others.
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Chronic Disease
develops more slowly than an acute disease, is usually less severe, and persists for a long, indeterminate period.
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Cohort Group
is a study group that has a known exposure to a risk factor; this group is selected and monitored in time; the incidences of disease of those people exposed to the risk factor and of those who were not exposed are then compared.
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Colonization
implies an establishment of microbial growth on or within the host
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Commensalism
a symbiotic relationship between two species in which one benefits and the other one neither benefits nor is harmed by the relationship.
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Common Source Epidemic
outbreak of disease due to contaminated food, water, or other single source of the infectious agent. An outbreak where there is a rapid rise and fall in the numbers of people who become ill, it is likely they were all exposed to a single common source of the infectious agent.
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Communicable Disease
diseases that can be transmitted from one person to another; example, the common cold or influenza.
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Descriptive Study
done after a disease outbreak to describe the characteristics of the ill persons involved and the place and time of the outbreak
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Direct Contact
mode of disease transmission requiring person-to-person body contact.
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Disease
describes a noticeable impairment of body function.
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Droplet Transmission
spread of respiratory disease over distances of less than 1 meter through inhalation of large respiratory droplets.
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Endemic
diseases that are constantly present in a given population.
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Endotoxins
a toxin incorporated in gram-negative bacterial cell walls and released when the bacterium dies (also called lipopolysaccharide).
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Epidemic
referring to a disease that has a higher than normal incidence in a population over a relatively short period of time.
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Exotoxins
a soluble toxin secreted by microbes into their surroundings, including host tissues (proteins).
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Focal infection
an infection confined to a specific area from which pathogens can spread to other areas.
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Fomites
a nonliving substance (inanimate object), such as clothing, dishes, or money capable of transmitting disease.
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Herd Immunity
the concept that an entire population is protected from infection by a particular pathogen when 70% of the population is immune to that pathogen (also called group immunity).
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Horizontal spread
diseases that are transmitted by person-to-person contact; examples include hand shaking, kissing, and sexual contact.
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Incidence rate
the number of new cases of a particular disease per 100,000 population seen in a specific period of time.
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Incubation period
the time between infection and the appearance of signs and symptoms.
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Indirect transmission
transmission of disease through fomites or inanimate objects.
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Infectious dose
number of organisms required to initiate disease.
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Latent disease
a disease characterized by periods of inactivity either before symptoms appear or between attacks.
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Leukocidin
an exotoxin produced by many bacteria, including the streptococci and staphylococci that kill phagocytes.
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Local infection
an infection confined to a specific area of the body.
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Mixed infection
an infection caused by several species of organisms present at the same time.
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Morbidity rate
the number of persons contracting a specific disease in relation to the total population (cases per 100,000); the number of cases divided by the population at risk.
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Mortality rate
the number of deaths from a specific disease in relation to the total population; the fraction of people who die from the disease.
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Mutualism
a symbiotic relationship in which both partners benefit.
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Normal microbial flora
the microorganisms that grow on the external and internal surfaces of the body without producing obvious harmful effects to these tissues.
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Nosocomial infection
an infection acquired during a hospitalization.
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Opportunists (opportunistic organisms)
an organism that does not ordinarily cause disease but can do so when the host defense mechanisms are impaired.
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Pandemic
a worldwide epidemic.
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Parasitism
a symbiotic relationship in which one organism, the parasite, benefits from the relationship, whereas the other organism, the host, is harmed by it.
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Prevalence rate
the number of people infected with a particular disease at any one time.
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Propagated epidemic
outbreak of contagious disease in which the infectious agent is transmitted to others, resulting in a steady increase in the numbers of persons becoming ill.
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Prospective study
a study that looks ahead to see if the identified risk factors can predict a tendency to develop the disease.
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Retrospective study
a study done following a disease outbreak; looks back to compare the actions of and events surrounding those who developed the disease with those who did not develop the disease (controls).
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Secondary infection
infection that follows a primary infection.
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Septicemia
an infection caused by rapid multiplication of pathogens in the blood (also called blood poisoning).
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Sign
a disease characteristic that can be observed by examining the patient, such as swelling or redness.
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Subacute disease
a disease that is intermediate between an acute and a chronic disease.
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Subclinical infection or disease
a disease lacking obvious symptoms.
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Superantigens
a type of exotoxin that reacts with a part of the T cell receptor not concerned with antigen recognition, thereby stimulating activity nonspecifically in many T cells and leading to illness and sometimes fatal shock.
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Superinfection
a secondary infection resulting from the removal of normal microbiota, allowing colonization by pathogenic, and often antibiotic- resistant microbes.
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Symptom
a disease characteristic that can be observed or felt only by the patient, such as pain or nausea.
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Syndrome
a combination of signs and symptoms that occur together.
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Systemic infection
an infection that affects the entire body (also called generalized infection).
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Toxoid
an exotoxin inactivated by chemical treatment but which retains its antigenicity and therefore can be used to immunize against the toxin.
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Transient microbial flora
microorganisms that inhabit the body only occasionally.
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Vector (biological)
an organism that actively transmits diseases through injecting an infectious agent into another host while taking a blood meal; the pathogen completes part of its life cycle within the organism (examples are mosquitoes, fleas, and ticks).
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Vector (mechanical)
organisms that transmit diseases passively on their feet and body parts (examples are houseflies.
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Vertical spread
diseases passed directly from a pregnant woman to the fetus or mother to a newborn.
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Virulence
the relative ability of a pathogen to overcome body defenses and cause disease; properties of microorganisms that assist pathogenicity.
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Virulence factors
a structural or physiological characteristic that helps a pathogen cause infection and disease.
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Zoonosis
a disease of animals that can be transmitted to humans.
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