acquired immunity—resistance to a disease that results from prior exposure to an infectious agent, its antigens, or by transfer of antibodies.
active immunity—resistance developed by the body in response to an infection or vaccine.
active surveillance—when the public health department or agency requests information or reports concerning public health conditions.
age-adjusted mortality rate—the mortality rate that has been adjusted to eliminate the effect of age among populations.
agent—a factor which causes disease or adverse health conditions; the agent can be a pathogen, a chemical, or form of energy.
age-specific mortality rate—a mortality rate limited to a particular age group; the number of deaths in the age group divided by the number of people in the age group, usually per 100,000.
AIDS—Acquired Immune Deficiency Syndrome—a syndrome caused by the human immunodeficiency virus.
allergy—a response to an allergen.
alternate hypothesis—in epidemiology, the hypothesis that exposure to a disease is directly linked to the health condition under study.
antibody—a protein produced by the body in response to a foreign substance; usually produced to fight disease.
antigen—any substance recognized by the body as foreign and that stimulates the production of antibodies.
antiretrovirus therapy—medications for the treatment of infections by retroviruses, particularly HIV; therapy usually consists of a combination of three or four different drugs.
analytic epidemiology—the field of epidemiology that studies why and how health-related events could occur, including the rates of disease occurrence differences in demographics, behaviors, environmental exposures, and other risk factors.
applied epidemiology—the field of epidemiology that addresses public health issues, such as communicable diseases or the environmental effects on cancer rates.
arbovirus—any virus transmitted through hosts by mosquitos, ticks, or other arthropods.
arthropod—an organism with jointed appendages and external skeletons.
association—the statistical relationship between two or more events or characteristics.
asymmetrical—not being identical on both sides of a central line; often called a skewed distribution.
attack rate—a measure of the proportion of people who experience an adverse health condition during a limited time period; the number of new cases during an outbreak period of time divided by the size of the population at the beginning of the period. Attack rate is usually expressed as a percentage or as the number per 1,000 or per 100,000 people.
attribute—a risk factor that is a characteristic of the person, animal, plant, or other organism under study, such as age, sex, weight, or genetic predisposition.
autoantibody—an antibody produced by an organism that targets the organism’s own cells or tissues.
autoimmune disease—condition that results from misdirected immune responses which are launched against the body’s own cells.
autoimmunity—immune responses of an organism against its own cells and tissues.
axis—one of the lines on a graph; the x-axis is the horizontal axis and the y-axis is the vertical axis.
bacteria— one-celled, prokaryotic organisms which are involved in fermentation, nitrogen fixation, and infectious disease.
bar chart—a graph in which each data value is represented by a bar or column.
bar chart, 100% component—a stacked bar chart in which all bars are the same length and the measured axis represents 0-100%.
bar chart, deviation—a bar chart which shows either positive or negative differences from a baseline.
bar chart, grouped—a bar chart which shows quantities of two variables using bars or columns separated by a space between the groups.
bar chart, stacked—a bar chart which shows quantities of two variables using subdivided bars or columns separated by a space between the columns.
basophil—white blood cell that secretes histamine; promotes an inflammatory response.
B cells—a lymphocyte that produces antibodies that bind to an antigen.
bias—a certain tendency or inclination that prevents unprejudiced consideration of a question or decision that can lead to inaccurate conclusion.
bimodal—having two data peaks.
biologic transmission—transfer of an infectious agent by a vector; the vector is usually a key part of the agent life cycle and harbors the agent before it is transferred to the host..
birth cohort—a group of individuals born at a similar time.
birth rate, crude—the number of live births during a period divided by the mid-period population; usually as births per 1,000 population.
B-lymphocytes—lymphocytes produced in the bone marrow that mature and develop in other lymphatic tissues.
box plot—a graph that displays data in a “box and whiskers” format to indicate minimum and maximum value (the ends), the interquartile range (the length of the box), and the median (line through the box.)
capillary—a small, blood vessel that connects a venule and an arteriole.
carrier—a person or animal that bears an infectious disease agent and can transmit it to other, but usually does not demonstrate any signs of the disease.
case-an instance of a disease or injury.
case definition—in epidemiology, a description of specific conditions and details that should be met in order for the person to be identified as having a particular disease or other health condition.
case-fatality rate—the proportion of people with a particular condition who die from that condition; the number of deaths divided by the number of persons having the condition x 100.
Example: in an outbreak of 20 cases, 3 people died. The case fatality rate was 3/20 or 15%.
case, index—the first case of a particular health condition of which health authorities are aware.
case, source—the case or instance of a patient response for transmitting an infection to others; the patient who gives rise to an outbreak or epidemic.
cause, necessary— a factor that must be present for a disease or other health problem to occur.
cause-specific mortality rate—the mortality rate from a specific cause in a population; the number of deaths from the specific cause divided by the size of the population at the midpoint of the time period.
cause, sufficient—the minimum conditions or events which must be present or met to produce a specific disease.
census—a count of a population which usually includes age, sex, occupation racial/ethnic group, marital status, and birth history.
central tendency—a measurement of the middle or center of a distribution of values or numbers; includes mean, median, and mode.
Cestoda—the class to which the tapeworms belong.
chain of infection—the movement of an infectious agent from one host by way of a transmission process to infect another susceptible host.
cilia—short, hair-like structures by which some microorganisms move.
ciliate—a protozoan that moves by cilia.
clinical criteria—the medical features that describe a specific health condition case; includes symptoms, medical findings, and lab results.
clinical disease—a disease that is at a state in which it shows its symptoms.
clinical trial—an experimental study that tests a variable and collects data from individual persons and follows the person’s health condition to determine the effects of the variable tested.
cluster—a group of cases of a disease, injury, or other health condition in an area during a particular period.
cohort—a group of persons having a common experience or exposure in a cohort study; used to study a disease or condition.
cohort, birth—a group of persons born during a particular period or year.
common-source outbreak—an outbreak that occurs from persons being exposed to the same harmful effect, such as the same infectious agent or toxin.
comparison group—a group used to compare results or data obtained in the experimental group.
contact—a person who has been exposed to a source of infection.
contact, direct—exposure or transmission of an infectious agent through touching; includes human-to-human contact and touching an infected animal, soil, or vegetation.
contagious—capable of being transmitted from one person to another by contact or close proximity.
control—in a case-control study, a member of the group of persons without the health problem under study.
control study case—a study or investigation that enrolls one group of persons with a certain disease or condition and a group of persons without the disease or condition (the control subjects) and compares the differences in a number of variables to test hypotheses and identify causes.
crude birth rate— the number of live births during a period divided by the mid-period population; usually as births per 1,000 population.
cytotoxic T cells—lymphocytes that produce chemicals that kill infected cells or tumor cells.
death-to-case ratio—the number of deaths from a particular disease, injury, or condition during a specific time divided by the number of new cases of the same condition identified during the same period of time.
decision tree—a branching chart depicting the logical sequence of events of a clinical or public health decision.
definitive host—the host that harbors the adult stage of a parasite.
demographic information—personal characteristics of a person or group, for example, age, sex, race/ethnicity, or occupation; used in descriptive epidemiology to identify patients or populations .
dendrogram—a branching chart that shows the evolutionary lines or genetic relatedness of organisms.
descriptive epidemiology—the field of epidemiology that organizes and summarizes data regarding persons who are affected by a disease or conditions, time of onset, and location.
direct transmission—immediate transfer of a pathogen from one site or organism to a host by direct contact or droplet spread.
disease—a condition in which the body cannot function normally due to infection by a pathogenic agent, genetic condition, nutritional deficiency, or an illness of an affected body organ.
distribution—the frequency and pattern of health-related characteristics and events in a population.
dose response—the relationship between an exposure and a health outcome as the amount of exposure (the dose) increases.
droplet nuclei—dried droplets of infectious agents that are inhaled and exhaled and remain suspended in air for long periods of time; can be blown over distances.
droplet spread—the direct transmission of an infectious agent through sneezing, coughing, or talking and that travel only a short distance before falling to the ground.
effect—the result of a cause.
effectiveness—the ability of an intervention to produce the intended or desired results.
efficacy—in epidemiology, the ability of a medical intervention or program to produce expected results under ideal conditions.
efficiency—in epidemiology, the effectiveness of a medical intervention or program to produce results with minimum time and resources.
EIS—Epidemic Intelligence Service—the CDC’s two-year training program in applied epidemiology for public health professionals.
endemic—a constant presence of a health condition within an area or population.
endotoxin—poisons that are part of the bacterial cell wall that are released when the bacteria adheres to a host cell.
exotoxin—a poison excreted by a microorganism.
environmental factor—a factor in the environment that affects a pathogen and the opportunities for exposure to it. Examples include geology, climate, insects, sanitation, or quality of health services.
epidemic—numbers of disease cases, injuries, or other health conditions greater than expected in an area or population during a particular period.
epidemic curve—a graph that plots the course of an outbreak by time of onset.
epidemic period—the time span of an outbreak or epidemic.
epidemiologic triad—in epidemiology, the model of infectious disease consisting of three components: an infectious agent, a susceptible host, and an environment that allows the two to come together.
epidemiology—the branch of medicine that studies patterns and causes of health-related conditions and uses those studies and results to control a health problem.
epidemiology, analytic—the field of epidemiology that studies why and how a health problem occurs. Analytic epidemiology uses comparison groups to find out how outbreak cases can be quantified and to form hypotheses about the cause of the outbreak.
epidemiology, descriptive—the field of epidemiology that organizes and summarizes data concerning infected persons, time, and locations of outbreaks.
epidemiology, field—the field of applied epidemiology that involves the control and prevention of health problems when epidemiologists must travel to and work in communities whre the health problem is occurring.
eukaryotic—an organism whose cells have specialized, membrane-covered organelles.
experimental study—a study in which an investigator tests a type of exposure for each person or community and follow the health status to determine the effects of the exposure.
exposed group—a group of people who have had contact with a suspected health problem.
exposure—having come into contact with a cause of a suspected health problem.
false-negative—a negative test result for a person who actually has the disease.
false-positive—a positive test result for a person who actually does not have the condition.
filovirus—any of the viruses belonging to the family Filoviridae; single-stranded RNA viruses that cause hemorrhagic fevers, including the Ebola and the Marburg viruses.
fission—a form of asexual reproduction; the splitting of an organism into two parts.
flagellum—a structure that allows cells to be motile; usually has a core of 9 + 2 array of microtubules.
follow-up study—a study performed to find out if there has been a change in conditions or patients since the initial study was performed.
fomite—an inanimate object that can transmit an infectious agent, such as bedding, towels, or surgical instruments.
frequency—the amount of number of occurrences of a characteristic or health outcome among a population.
frequency distribution—a summary of the values or categories of a variable; usually displayed in a two-column table with the individual values or categories in the left column and the number of observations in the right column.
Gram stain—a type of stain used to identify bacteria as being either Gram positive or Gram negative, depending on the chemical characteristics of the bacterial cell wall.
graph—a diagram that displays a group of data arranged on axes.
health—the state of complete physical, mental, and social well-being.
health indicator—any characteristic or measure that indicates the state of health of a population, such as morbidity or mortality rates.
health information system—a combination of health statistics from different sources that are used to provide information about health status, care, services and programs on health
helper T cell—a lymphocyte that stimulates mitotic divisions that result in the production of increased numbers of T cells after contact with an antigen.
herd immunity—resistance to an infectious agent by an entire group or community; a large number of immune persons in a community reduces the likelihood that an infected person will come into contact with a susceptible person among the population.
hermaphroditic—having both male and female reproductive organs in the same individual.
high-risk group—a group of persons who has a higher risk for a particular disease, injury, or other health condition than the rest of the community or population.
histogram—a graph using bars or columns to represent values in a statistical study; in epidemiology, time is usually plotted on the x-axis with number of cases on the y-axis.
HIV—Human Immunodeficiency Virus-a retrovirus that causes AIDS by infecting helper T cells of the immune system.
host—an organism that has an infectious agent living on or in it under natural conditions.
host factor—any factor such as age, race/ethnicity, gender, or behavior) that affects a person’s response to an infectious agent.
hyperendemic—the constant presence at high levels of an agent or health condition in a given area or population.
hypothesis—an idea or explanation for something that is based on known facts but has not yet been proven.
immune system—a body system that protects against disease and foreign substances, destroys infected cells, and removes cellular debris.
immunity, active—resistance developed in response to an infecting agent or vaccine usually resulting in the production of an antibody produced by the host.
immunity, herd—resistance to an infectious agent by an entire group or community; a large number of immune persons in a community reduces the likelihood that an infected person will come into contact with a susceptible person among the population.
Note: Herd immunity can come about through vaccination of a large number of people in a population that results in unvaccinated people not being exposed to the pathogen and thereby being protected. Particularly important in protecting people who cannot be vaccinated ie children too young, people too sick (cancer, etc), and those with immune system problems. If immunization rates fall, head immunity can break down. Increased cases of measles in the UK and outbreaks of pertussis in the US are examples of decreasing herd immunity.
immunity, passive—immunity resulting from an antibody produced in another host, such as antibodies received by an infant from its mother, or vaccination.
immunological memory—the characteristic of the immune response that involves lymphocytes’ ability to recognize an antigen in the future that it encountered in a previous immune response.
immunological specificity—the characteristic of the immune response that involves lymphocytes’ ability to engage with a particular type of antigen.
immunology—the study of the immune system and the processes of the immune response against disease.
incidence—a measure of the frequency of new cases of disease, injury, or other health condition in a population during a specific time period.
incidence proportion—the number of new cases of illness, injury, or other health condition divided by the size of the population at the start of the time period.)
incidence rate—the probability of developing a specific disease during a given period of time; the number of new cases over a time period divided by the average population of the time period.
incubation period—the time period from exposure to an infectious agent to the onset of symptoms of disease.
independent variable—a variable being observed or measured that is hypothesized to have an effect on a dependent variable.
infection—a condition in which an infectious agent invades the body and begins to multiply.
inflammation—a tissue response that includes an accumulation of fluid and cells in the affected area.
index case—the first case of a particular health condition of which health authorities are aware.
indirect transmission—transfer of an infectious agent by air, by object, or by a vector.
infant mortality rate—the number of deaths of infants under one year of age per 1,000 live births in a given year.
infection—the invasion of body tissues by an infectious organism; does not have to cause disease conditions.
infectivity—the ability of an infectious organism to cause disease.
inflammation—a tissue response that includes an increase of fluid in the affected area.
information bias—information characterized by a certain tendency or inclination that prevents unprejudiced consideration of a question or decision; can lead to inaccurate conclusions.
interferon—a substance produced by the cells that inhibits the replication of viruses.
interpandemic—the period between pandemics.
interstitial fluid—fluid within cells.
interquartile range—the measure of the middle 50% of a set of data; the difference between the third quartile (75th percentile) and the 1st quartile (25th percentile).
isolation—the separation of infected persons from the rest of a population to prevent transmission. (Quarantine is the separation of well persons who may have been exposed to the disease agent.)
larval stage—an immature stage in a life cycle between the egg and the adult.
latency period—the time period from exposure to an agent (usually noninfectious) and the onset of symptoms.
life expectancy—the average number of years a person can expect to live.
line listing—in epidemiology, a spreadsheet list of cases or patients with information about each patient, including gender, age, and date of onset of symptoms.
longitudinal study—a study performed over a period of time so that effects of time is measured as a variable on the conditions.
lymph—fluid transported in the lymphatic system.
lymph node—a mass of lymph tissue located along lymphatic pathways in the body which function in immunity.
lymphocyte—a type of white blood cells that fights pathogens in the body.
macrophage—a large cell that engulfs and destroys disease-causing agents and cell fragments in the body.
Mast cell—a cell in tissue that release histamine into tissue fluid.
mean, arithmetic—the mean calculated by adding all the values in a group of data and dividing by the number of values in the group.
mean, geometric—the mean of a set of data measure on a logarithmic scale.
measure of central location—data that includes the mean, median, and mode; also called measure of central tendency.
measure of spread—a measure of data out from its central value; in epidemiology, includes the interquartile range, variance, and the standard deviation.
mechanical transmission—transfer of an agent by a vector that is not part of the biologic life cycle of the infectious agent.
median—the middle number or amount in a series of numbers or data.
medical surveillance—monitoring a person who may have been exposed to an infectious disease or harmful chemical or radiologic agent.
microorganism—an organism too small to be seen without a microscope.
midrange— the halfway point, or midpoint, in a set of observations.
mode—the most frequently occurring value in a set of observations.
mode of transmission—the method of transmission of an infectious agent from its reservoir to its host.
monocyte—a type of white blood cell that can engulf larger foreign particles in the blood.
mortality rate—the rate or frequency of death in a population during a specific time period.
mortality rate, age-specific—a mortality rate calculated for a particular age group; the number of deaths in the age group divided by the number of people in that age group, usually multiplied by 100,000.
mortality rate, infant—the number of deaths of infants under one year of age per 1,000 live births in a given year; a universally accepted indicator of the health of a nation’s population and the quality of its healthcare system.
mortality rate, sex-specific—the mortality rate among either males or females.
natural history of disease—the course of a disease process in a person from the time it begins to the time it ends, in the absence of treatment.
NCHS—the National Center for Health Statistics—a component of the Centers for Disease control and Prevention, a U.S. governmental organization that is responsible for national health statistics and surveys.
necessary cause— a factor that must be present for a disease or other health problem to occur.
Nematoda—the phylum to which the round worms belong.
neonatal mortality rate—the ratio of the number to deaths in the first 28 days of life to the number of live births occurring in the same population during the same period of time.
neutrophil—a type of white blood cells that can engulf smaller foreign particles in the blood.
NIH—National Institutes of Health—an agency of the United States Department of Health and Human Services that is the primary agency of the US government responsible for biomedial and health-related research.
NIAID—National Institute of Allergy and Infectious Diseases—the branch of the National Institutes of Health that researches to understand, treat, and prevent infectious, immunologic, and allergic diseases.
non-specific defense mechanism—any general mechanism that protects the body against a variety of pathogens.
normal distribution—a group of data represented in distribution of random variables as a symmetrical bell-shaped graph.
notifiable disease—a disease that must be reported to public health officials by law.
null hypothesis—a hypothesis that maintains that there is no significant difference between two sets of data and that any observed difference is due to sampling or experimental error.
numerator—the top number of a fraction.
outbreak—the sudden rise in the occurrence of a disease or injury in a given area during a given time period; generally considered to be more localized than an epidemic.
outbreak, common-source—an outbreak that occurs from persons being exposed to the same harmful effect, such as the same infectious agent or toxin.
outbreak, point-source—a type of source for an outbreak in which the exposure period is brief so that all cases of infection occur within one incubation period.
outbreak, propagated—an outbreak that spreads from person-to-person; not a common source outbreak.
outlier—a value that is markedly different from other values in a sample.
pandemic—an epidemic that occurs over a widespread area and affects a large proportion of the population.
parameter—a measured value, such as body temperature, that characterizes a process.
parasite—an organism that lives in or on a host organism for at least part of its life cycle.
passive immunity—immunity resulting from an antibody produced in another host, such as antibodies received by an infant from its mother or by receiving an artificially prepared antibody injection.
passive surveillance—when health conditions and monitored and the data are sent to health agencies without being requested.
pathogen—any disease-causing agent.
pathogenicity—the ability of an infectious agent to cause disease after infection; measured by the finding the proportion of infected persons who actually get sick.
percentile—each of one hundred set of points that a population can be divided into based on a variable. For example, the 10th percentile is a point at which 10% of the observations for the variable fall below and the other 90% fall above.
phagocytosis—the process of engulfing a smaller cell, microorganism, or foreign particle.
pie chart—a circular graph of data in which each segment of the pie is proportional to the amount in the distribution.
point-source outbreak—a type of source for an outbreak in which the exposure period is brief so that all cases of infection occur within one incubation period.
population—the number of persons in a geographic area or the number of persons in a particular group, such as the number of people who attend a certain school.
portal of entry—the pathway by which an infectious agent can enter its host. For example, the influenza virus’s portal of entry is host’s respiratory tract.
portal of exit—the pathway by which an infectious agent can leave its host. For example, the influenza virus’s portal of exit is the host’s respiratory tract (coughing or sneezing).
prevalence—the number of cases or events in a given population.
proglottid—segments of a tapeworm body.
prokaryotic—a single-celled organism which lacks membrane-covered organelles.
propagated outbreak—an outbreak that spreads from person-to-person; not a common source outbreak.
Protista—the Kingdom of Protists, including chytrids, water molds, slime molds, protozoans, sporozoans, euglenoids, dinoflagellates, and the red, brown, and green algae.
protozoan—a group of protists, including the sarcodines, ciliates, sporozoans, and flagellates.
pseudopodia—structure used for movement formed by cytoplasmic streaming.
quarantine—a period of time in which a person or animal suspected of having an infectious disease is kept away from other people or animals; the separation of potentially exposed persons.
random sample—a small group of persons chosen by chance and not according to a plan or pattern, each one has the same probability of be selected.
range—in a set of data, the difference between the largest and smallest values.
ratio—a comparison of two numbers calculated by dividing one number by the other.
representative sample—a small group whose characteristics match those of an original or a reference population.
reservoir—in epidemiology, the location in which an infectious agent normally lives; includes humans, animals, plants, or the environment.
resistance—the ability to withstand disease.
risk—the likelihood or probability that an event, such as an illness or injury, will occur.
risk factor—any factor which increases the likelihood of developing a disease or injury; includes lifestyle, environmental exposures, or heredity characteristics.
R0—(pronounced R naught)—the basic reproduction number; the average number of people each infected person will infect in a population that has no immunity to the disease.
sample—a small group of people selected to be tested to obtain information about a larger group.
sample, random—a small group of persons chosen by chance and not according to a plan or pattern, each one has the same probability of be selected.
sample, representative—a small group whose characteristics match those of an original or a reference population.
saprobe—heterotrophs that obtain energy and carbon from non-living organic matter, causing decay).
sarcodine—a protozoan that moves by amoeboid structures.
scolex—head of a flatworm.
seasonality—change in status that occurs during a regular seasonal pattern. Examples include respiratory tract viral infections, flus, E. coli infections in Argentina, measles in Niger
secondary attack rate—the probability that an infection occurs among susceptible people within a reasonable time after contact with an infectious person or other infectious source.
secular trend—a long-term change in disease or death rates for a specific health condition in a specific population.
selection bias—a tendency that prevents an unprejudiced evaluation of a question or decision.
self-marker—a particular molecular structure on every cell that immune response cells in the body can recognize as “self”.
sensitivity—the ability of a clinical test, case definition, or surveillance system to accurately identify a health condition.
sentinel surveillance—monitoring a health situation in which healthcare sources, such as physicians, hospitals, or clinics, send in all cases of one or more notifiable diseases.
SIR model—mathematical model that considers the number of people susceptible (S), infected (I), and removed by recovery or death (R) during an infectious disease outbreak.
skewed—a distribution that is not symmetrical.
source (of infection)—the person, animal, object, or substance from which an infectious agent is transmitted to a host.
source case—the case or instance of a patient response for transmitting an infection to others; the patient who gives rise to an outbreak or epidemic.
specific defense mechanism—any mechanism that provides protection against a specific disease.
spectrum of illness the range of manifestations a disease process can take (e.g., from asymptomatic to mild clinical illness to severe illness and death).
spirillum—spiral-shaped bacteria belonging to the genus of Gram-negative bacteria.
spleen—a large organ located in the upper left abdomen that functions as a blood reservoir and filter.
sporadic—an event that is not continuous or regular.
sporozoan—a protozoan that usually has no method of movement and is a parasite.
spot map—a map showing points where each person affected with a disease or condition lives, works, or may have been exposed.
standard deviation—the variation of a variable around its mean; calculated as the square root of the variance. A low standard deviation indicates that data points are close to the mean; a high standard deviation indicates that data points are spread out from the mean.
standard error (of the mean)—the standard deviation of sample means of a variable when compared to the true population mean of that variable; the standard deviation of the variable divided by the square root of the sample size.
statistical significance—a measure of how likely it is that data results could have occurred by chance alone; based on the degree of association between an independent variable and a dependent variable.
study, case-control—a study that includes one group of persons with a certain disease, condition, or injury and another group of persons without the disease, condition or injury and compares the differences between the groups.
study, cohort—a group of persons having a common experience or exposure in a cohort study; used to study a disease or condition.
study, experimental—a type of study in which the investigator decides on a type of exposure for each person or community in the study and then follows the effects of the exposure.
study, observational—a study in which the investigator only observes characteristics for persons or a community rather than deciding on the type of exposure to be studied.
subclinical—having no symptoms.
surveillance, active—a survey in which a health agency solicits reports from the public, including patients, citizens, and healthcare officials.
surveillance, medical—monitoring a person who may have been exposed to an infectious disease or harmful exposure to a chemical or radiologic agent.
surveillance, passive—monitoring health conditions in which data are sent to health agencies without being asked to send them.
surveillance, sentinel—monitoring a health situation in which healthcare sources, such as physicians, hospitals, or clinics, send in all cases of one or more notifiable diseases.
survey—a set of questions in order to collect information.
survival curve-a line graph that begins with 100% of the population being studied and continues to display the percentage of the population still surviving at various points in time.
symmetrical—a type of distribution on a graph where the shapes to the right and left of a central location are the same; a normal, bell-shaped curve is an example.
symptom—any indication of disease noticed or felt by a patient.
syndrome—a combination of symptoms characteristics of a disease or condition, such as AIDS-Acquired Immunodefiency-Disease Syndrome.
thymus—a two-lobed organ located behind the sternum and between the lungs which functions in providing immunity.
T-lymphocytes—lymphocytes produced in bone marrow which travel to the thymus where they develop into specialized disease-fighting cells.
transmission of infection—any mechanism by which an infectious agent is spread to a host.
transmission, airborne—transfer of an infectious agent through the air; an indirect transmission.
transmission, biologic—transfer of an infectious agent by a vector; the vector is usually a key part of the agent life cycle and harbors the agent before it is transferred to the host; an indirect transmission
transmission, direct—transfer of an infectious agent to a host by direct contact
transmission, indirect—transfer of an infectious agent by air, by object, or by a vector.
transmission, mechanical—transfer of an agent by a vector that is not part of the biologic life cycle of the infectious agent.
transmission, vectorborne—transfer of an infectious agent by a vector such as a tick, mosquito, or flea; an indirect transmission.
transmission, vehicleborne—transfer of an agent by an inanimate object; includes food or water.
Trematoda—the class to which the flukes belong.
trend, secular—a change that occur over years or decades.
variable—any characteristic that can be measured and have different values.
variable, dependent—a variable whose values are a function of one or more other variables.
variable, independent—a variable being observed or measured that is hypothesized to have an effect on a dependent variable.
variance—a measure of the spread in a set of observations; the sum of the squares of deviations from the mean divided by the number of observations minus 1.
vector—a living organism such as an insect or arthropod that carries a disease-causing agent from one host to another in the life cycle of a pathogen.
vehicle—a non-living object that carries a disease-causing agent from one host to another in the life cycle of a pathogen.
virology—the study of viruses.
virulence—the ability of a pathogen to cause serious disease.
virus—an infectious agent that multiplies only within the cells of living hosts; composed of RNA or DNA and a protein coat; more complex viruses also have a surrounding envelope.
vital statistics—data recorded about births, deaths, marriages, and divorces.
x-axis—the horizontal axis on a line or bar graph.
y-axis—the vertical a on a line or bar graph.
zooflagellates—a protozoan that moves by one or flagella.
zoonosis—an infectious disease transmitted from animals to humans.
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