Basic Epidemiological and Public Health Terms (Disease Detectives)

cohort study disadvantages

time consuming, expensive

vehicle transmission

transmission via a medium such as food, air, and liquid, which are all routinely taken into the body, and thus serve as vehicles into the body.

trial disadvantages

unethical for harmful exposures, time consuming, most expensive

vector example

a moquito that transmits the malaria protozoan

susceptible host

a person who cannot resist a microorganism invading the body, multiplying, and resulting in infection

cross-sectional

a survey, health questionnaire, "snapshot in time"

virus

a very small infectious agent that only replicates in living hosts

odds ratio

used in case-control study

relative risk

used in cohort study

propagated (progressive source) shape

usually contains a series of successively larger peaks, reflective of the increasing number of cases caused by person-to-person contact, until the pool of those susceptible is exhausted or control measures are implemented. the distance between those peaks may be a rough indication of the incubation period of the disease. As the outbreak progresses, the peaks flatten out (think of the variance around a mean over multiple generation)

propagated (progressive source)

occur when a case of disease serves later as a source of infection for subsequent cases and those subsequent cases, in turn, serve as sources for later cases.

point source

occur when people are exposed to the same exposure over a limited, well defined period of time.

continuous common source

occur when the exposure to the source is prolonged over an extended period of time and may occur over more than one incubation period.

selection bias

when selection of participants for a study is affected by an unknown variable that is associated with the exposure and outcome being measured. An example of information bias is recall bias. When studied, some subjects may more easily recall specific habits related to a disease or condition than subjects not affected with the disease or condition.

2*2 table

table which has two columns and rows for people with or without exposure and with or without disease; shows amount of people with each characteristic

risk is the same as. . .

the Incidence (see below) and the terms are used interchangeably

common portal of entry

the mucous membrane of the respiratory tract

attack rate

the rate that a group experienced an outcome or illness equal to the number sick divided by the total in that group (there should be a high attack rate in those exposed and a low attack rate in those unexposed)

random error

the result of fluctuations around a true value because of the sample population. Random error can result from poorly worded questions or misunderstanding of questions. As the term implies, it is random, so it is impossible to correct. However, random error can be reduced; some ways include increasing the sample size and making measurements more precise, either by using a more accurate measurement device or by taking more trials. While these techniques would increase random error, they can also be expensive. Better measurement devices will cost more, and more trials and a larger sample size will mean more work. Precision is a measure of random error that is inversely related, so increasing random error decreases precision.

Hill's Criteria for Causation

nine criteria that must be met to establish a cause-and-effect relationship

vector transmission

no entry

prevalence

number of affected persons in the population at any given point in time

incidence

number of new instances of disease in a population over a given time period

trial advantages

most scientifically sound, best measure of exposure

outbreak

(localized epidemic) More cases of a particular disease than expected in a given area or among a specialized group of people over a particular period of time.

chain of transmission triad

1. an external agent 2. a vector or fomite that transmits the disease 3. a suspectible host for the disease

portal of entry

An opening allowing the microorganism to enter the host; the route a pathogen takes to enter a host. Just as with the portals of exit, many pathogens have preferred portals of entry. Many pathogens are not able to cause disease if their usual portal of entry is artificially bypassed.

parasite

An organism that depends on another organism.

agent

A factor, such as a microorganism, chemical substance, or form of radiation, whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of a disease; a microbial organism with the ability to cause disease

fomite

A physical object that serves to transmit an infectious agent from person to person.

portal of exit

A place of exit providing a way for an agent to leave the reservoir; the route a pathogen takes out of an infected host. portals of exit tend to be fairly well defined. What serve as portals of exit are often not terribly surprising, at least, once something is known of how and where a pathogen replicates and enters new hosts

reservoir

A place where agents can thrive and reproduce.

plague

A serious, potentially life-threatening Infectious disease that is usually transmitted to humans by the bites of rodent fleas. It was one of the scourges of our early history. There are three major forms of the disease: bubonic, septicemic, and pneumonic.

cluster

An aggregation of cases over a particular period esp. cancer & birth defects closely grouped in time and space, regardless of whether the number is more than the expected number. (often the expected number of cases is not known.)

vector

An animal that transmits disease. an animate intermediary in the indirect transmission of an agent that carries the agent from a reservoir to a susceptible host.

pandemic

An epidemic occurring over a very wide area and usually affecting a large proportion of the population.

zoonosis

An infectious disease that is transmissible from animals to humans.

epidemic

Large numbers of people over a wide geographical area are affected.

mortality

Measure of the frequency of the disease.

mode of transmission

Method of transfer by which the organism moves or is carried from one place to another; the transfer of disease-causing microorganisms from one environment to another, particularly from an external environment to a susceptible individual.

classical epidemiology

Population oriented, studies community origins of health problems related to nutrition, environment, human behavior, and the psychological, social, and spiritual state of a population. The event is more aimed towards this type of epidemiology.

endemic disease

Present at a continuous level throughout a population/geographic area; constant presence of an agent/health condition within a given geographic area/population; refers to the usual prevalence.

virulence

Severity of disease that the agent causes to a host.

clinical epidemiology

Studies patients in health care settings in order to improve the diagnosis and treatment of various diseases and the prognosis for patients already affected by a disease. These can be further divided into: •Infectious Disease Epidemiology - heavily dependent on laboratory support •Chronic Disease Epidemiology - dependent on complex sampling and statistical methods

infectivity

The capacity to cause infection in a suspectible host.

risk

The probability that an individual will be affected by, or die from, an illness or injury within a stated time or age span.

morbidity

The rate of incidence for a disease.

epidemiology

The study of distribution and determinants of health-related states in specified populations, and the application of this to control health problems.

fomite example

a comb infested with one or more head life would be a fomite or the dust particles containing infectious cold virus that remain after droplets of infected saliva are coughed into the air

surveillance

The systematic and ongoing collection, analysis, interpretation, and dissemination of health data. the purpose of public health surveillance is to gain knowledge of the patterns of disease, injury, and other health problems in a community so that we can work toward controlling and preventing them.

incubation period

Time in between when a person comes into contact with a pathogen and when they first show symptoms or signs of disease.

prevalence expression

X cases/ Y population

incidence expression

X cases/Y population/ Z time

chain of infection

agent leaves reservoir through portal of exit and is conveyed by some mode of transmission and enters the appropriate portal of entry to infect a susceptible host

systematic error

any error other than random error. For example, systematic error can occur if the markings on your ruler are wider. This would make the numeric measurements less than what they actually are, making all data collected inaccurate. However, trends observed may still be preserved (shifting a line vertically preserves a line, as it is a rigid motion).

food-bourne transmission

any number of pathogens are found in food and not killed during processing may be transmitted via food product. Salmonella especially tends to be part of the normal flora of chickens and consequently associated with chicken products.

confounding bias

bias resulting from mixing effects of several factors. Unlike selection and information bias, confounding bias deals with causation and not variations in study results.

case-control study advantages

can study rare disease, relatively less expensive and relatively fast

pathogenicity

capacity to cause disease in a host

case definition

clinical information, characteristics, location or place, time sequence

point source shape

commonly rises rapidly and contain a definite peak, followed by a gradual decline

case-control

compare people with and without disease to find common exposures

cohort

compare people with and without exposures to see what happens to each

ecological study

comparisons of geographical locations

droplet transmission

consequence of being coughed, sneezed, or spit on. To be considered droplet transmission, mucous droplets must still be traveling with the velocity imparted on it leaving the mouth. As a rule of thumb, this is up to one meter after exiting the mouth. Any further and this is considered airborne transmission. Given interaction within one meter of people is certainly more difficult to avoid droplet transmission than it is to avoid either direct or indirect transmission. Not surprisingly, it is especially respiratory diseases that are transmitted by droplets.

mode of transmission categories

contact, vehicle, and vector

four reasons why disease detectives study and research outbreaks and epidemics

control and prevention, research opportunities, training, and legal concern

Food Borne Illness prevention tactics

cook meat, poultry, and eggs thoroughly. don't cross contaminate one food with another. chill and refrigerate leftovers promptly. clean and wash all produce. report suspected food-borne illnesses to the local health department.

chronic disease epidemiology (clinical epidemiology)

dependent on complex sampling and statistical methods

contact transmission

direct (person-to-person), indirect (fomite), or droplet

continuous common source shape

down slope of the curve may be very sharp if the common source is removed or gradual if the outbreak is allowed to exhaust itself

secondary prevention

during the latent stage (when the disease has just begun), process of screening and instituting treatment may prevent progression to symptomatic disease

tertiary prevention

during the symptomatic stage (when the patient shows symptoms), intervention may arrest, slow, or reverse the progression of disease

primary prevention

early intervention to avoid initial exposure to agent of disease preventing the process from starting

cross-sectional study advantages

fastest, least expensive

water-bourne transmission

fecal contaminated water. Generally, this is via sewage contaminated water supplies. It is especially gastrointestinal pathogens that are present in feces and therefore which rely on this type of transmission.

infectious disease epidemiology (clinical epidemiology)

heavily dependent on laboratory support

epi-curves

histogram that shows the course of an outbreak by plotting the number of cases of a condition according to the type of onset

randomnized controlled trial

human experiment

analytic epi

hypothesis testing-study design

incidence vs. prevalence

incidence includes time. time reflects the duration of the illness of the illness or condition. if two conditions have the same incidence in a population, the one with the longer duration will have the greater prevalence

pandemic example

large numbers of people in several countries or continents affected

fungi

microorganisms that include yeast, mushrooms, and mold

bacteria

microscopic organisms that are often shaped as rods, spheres, or spirals

cohort study advantages

most accurate observational study, good measure of exposure

indirect contact

occurs from a reservoir via inanimate objects called fomites. Fomites are basically almost anything an infected individual or reservoir can touch, upon which can be left a residue of contagious pathogen. Exceptions include the various inanimates referred to as vehicles: food, air, and liquids. Typically, it is more difficult to avoid indirect contact transmission than it is to avoid direct contact transmission. A certain degree of organismal durability may be necessary to survive passage on a fomite. The best way to prevent indirect contact transmission is by avoiding contact with fomites, avoiding contact of hands with mucous membranes, especially when handling or potentially handling fomites, the use of barriers when handling fomites, and disinfecting fomites before handling.

direct contact

occurs through touching, kissing, etc . To prevent direct contact transmission, wear gloves and masks, etc.

airborne transmission

occurs via droplets (typically mucous droplets) where droplets are liquids that remain airborne whether as aerosols (very small droplets) or associated with dust particles. An example is within airliners where economizing measures reduces the turnover of cabin air and consequently increases air recycling. Organisms which can find their way into the air and remain viable thus have repeated opportunities to infect passengers. It requires greater organismal durability that droplet transmission simply because of the length of time the microorganism is exposed to the air, before infecting a new host, is longer. Increased durability is to the effects of desiccation, exposure to sunlight, etc. This is why breathing does not typically result in the acquisition of disease.

active immunity

occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response

parasites

organisms that derive a benefit from their host without giving one back

portals of entry to the nervous system

parenteral --> via the blood --> via the lymphatic systems --> peripheral nerve axons

descriptive epidemiology

person, place and time

cross-sectional study disadvantages

possible time-order confusion, least confidence in findings

case-control study disadvantages

possible time-order confusion, possible error in recalling past exposures

herd immunity

protecting a whole community from disease by immunizing a critical mass of its populace. Vaccination protects more than just the vaccinated person. By breaking the chain of an infection's transmission, vaccination can also protect people who haven't been immunized. But to work, this protection requires that a certain percentage of people in a community be vaccinated.

surveillance purpose

public health surveillance is to gain knowledge of the patterns of disease, injury, and other health problems in a community so that we can work towards their prevention and control.

quasi experiments

research similarities with traditional experiment design or RCT, but lack element of random assignment to treatment/control

portal of exit example

respiratory infections tend to utilize the mouth and nose as portals of exits. most common are the skin, gastrointestinal tract, and respiratory tract

quaternary prevention

set of health activities to mitigate or avoid consequences of unnecessary/excessive intervention of the health system. Social credit that legitimizes medical intervention may be damaged if doctors don't prevent unnecessary medical activity and its consequences.

passive immunity

short-term immunization by the injection of antibodies, such as gamma globulin, that are not produced by the recipient's cells. naturally acquired passive immunity occurs during pregnancy, in which certain antibodies are passed from the maternal into the fetal bloodstream