Disease Detectives

Classical Epidemiology

Population oriented an studies the community origins of health problems related to nutrition, environment, and human behavior

Clinical Epidemiology

Studies patients in health care settings in order to improve diagnosis, treatment, and prognosis

Infectious Disease Epidemiology

A subset of clinical epidemiology; heavily dependent on laboratory support

Chronic Disease Epidemiology

A subset of clinical epidemiology; dependent on complex sampling and statistical methods

Descriptive Epidemiology

Considers time/place/person data on a disease to determine trends; answers questions like who/what/where/when

Analytical Epidemiology

Involves hypothesis testing to determine the cause of disease (causal relations); answers questions like why/how

Disease

Infection that results in signs (objective) and symptoms (subjective)

Objective

Are signs subjective or objective?

Subjective

Are symptoms subjective or objective?

Opportunistic Disease

A disease that causes sickness when given the opportunity of a damaged or weakened immune system

Nosocomial Disease

An infection that is acquired in a hospital

Latrogenic Disease

An illness that is caused by medication or a physician

Chronic Infection

An infection where the agent is continuously present and detectable

Latent Infection

An infection where the agent is continuously present, but can remain dormant before reactivation

Incubation Period

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

Latent Period

Time in between when a person comes into contact with a pathogen and when they become infected

Asymptomatic

Displays no signs or symptoms but is infected and can carry the disease

Suseptibility

To what extent a member of a population is able to resist infection

Susceptible Individual

A member of a population at risk of becoming infected by a disease

Pathogenicity

The property of causing disease following infection

Virulence

The property of causing severe disease

Infectivity

The property of establishing infection following exposure

Morbidity

The rate of disease in a population

Mortality

The rate of death in a population

Case Fatality Rate

The rate of death due to a disease in a diseased population

Prevalence

The number of existing cases of disease in a given population

Point Prevalence

The number of existing cases of disease in a given population at a given point in time

Incidence

The rate of new cases of disease in a given population over a period of time

Attack Rate

The number of people infected, divided by the total sample; there should be higher rates in those exposed and a lower rate in those unexposed

Person-time

The sum of the time during which each individual in a population was at risk for a disease

Index Case

Also known as patient zero, the first case of a disease in a specific setting

Etiology

The cause of a disease

Pathology

The science of the study and diagnosis of disease and injury

Determinant

Any factor that brings about change in a health condition

Herd Immunity

A critical proportion of a population is immune to a disease such that the entire population is protected

Fulminant

A sudden and severe onset

Quarantine

What occurs when you may have been exposed

Isolation

What occurs when you have been exposed

Confirmed Cases

Lab confirmation combined with signs and symptoms

Probable Cases

Signs and symptoms but no lab confirmation

Possible Cases

Some signs and symptoms but unclear

Line listing

A chart of cases which includes identifying info, clinical info, time, person, place, and risk factors

PulseNet

A network of labs across US that helps identify new foodborne disease outbreaks; automatically reports data in real time to CDC; uses early detection/reporting and DNA fingerprinting

PFGE

Used to find DNA fingerprints, not as accurate as WGS

WGS

The main form of DNA fingerprinting that PulseNet uses

Data Dissemination

Also called distribution; announcements, reports, articles, and media give info to important ppl and public

Passive

Type of surveillance; diseases are reported by healthcare providers; simple and inexpensive, but often limited by incomplete reporting and quality variation

Active

Type of surveillance; health agencies contact health providers seeking reports, this ensures more complete reporting of conditions, often used with a specific investigation or during an outbreak

Syndromic

Type of surveillance; signs of the disease are monitored as a proxy for the disease itself; symptoms must be infrequent and severe enough to warrant investigation of each identified case and must be unique; often used when timeliness is key, diagnosis is difficult or time-consuming, or when detecting and defining scope of outbreak

Sentinel

Type of surveillance; professionals selected to represent a specific geographic area or group report health events to health agencies; used when high-quality data can’t be obtained through passive surveillance; involves monitoring trends or key health indicators and a limited network of reporting sites; easy to implement intervention earlier and not be reliant on doctors diagnosing; not as effective for detecting rare disease

Hill’s criteria for causation

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

Strength of Association

Relationship is clear and risk estimate is high

Consistency

Observation of association must be repeatable in different populations at different times

Specificity

A single cause produces a specific effect

Alternative Explanations

Consideration of multiple hypotheses before making conclusions about whether an association is causal or not

Temporality

Cause/exposure must precede the effect/outcome

Dose-Response Relationship

An increasing amount of exposure increases the risk

Biological Plausibility

The association agrees with currently accepted understanding of biological and pathological processes

Experimental Evidence

The condition can be altered, either prevented or accelerated, by an appropriate experimental process

Coherence

The association should be compatible with existing theory and knowledge including knowledge of past cases and epidemiological studies

Strength of association, consistency, specificity, alternative explanations, temporality, dose-response relationship, biological plausibility, experimental evidence, coherence

9 criteria for causation

Koch’s Postulates

Criteria to establish a causal relationship between a causative microbe and a disease

Koch’s Postulates

The microbe must be present in abundance in all cases of the disease but not in healthy organisms, the microbe must be isolated from the diseased organism and grown in a pure culture, the cultured microbe should cause disease when introduced into a healthy organism, the microbe must be reisolated from the inoculated, diseased experimental host and identified as identical to the original specific causative agent

Evan’s Postulates

1. The prevalence of the disease should be significantly higher in those exposed to the risk factor than those not.

2. Exposure to the risk factor should be more frequent among those with the disease.

3. In prospective studies, the incidence of the disease should be higher in those exposed to the risk factor.

4. The disease should follow exposure to the risk factor with a normal or log-normal distribution of incubation periods.

5. A spectrum of host responses along a logical biological gradient from mild to severe should follow exposure to the risk factor.

6. A measurable host response should follow exposure to the risk factor in those lacking a response before the exposure or increase the response in those with a response before exposure. A host response should be infrequent in those not exposed to the risk factor.

7. In experiments, the disease should occur more frequently in those exposed to the risk factor than in the control group.

8. Reduction or elimination of the risk factor should reduce the risk of disease.

9. Modifying or preventing host response should eliminate or decrease disease.

   1. All findings should make biological and epidemiological sense.

Convalescent

Type of vector/carrier; humans are capable of spreading disease following a period of illness, typically thinking themselves cured

Incubatory

Type of vector/carrier; when an individual transmits pathogens immediately following infection but prior to developing symptoms

Chronic

Type of vector/carrier; someone who can transmit a disease for a long period of time

Genetic

Type of vector/carrier; has inherited a disease trait but shows no symptoms

Transient

Type of vector/carrier; someone who can transmit an infectious disease for a short amount of time

external agent, susceptible host, environment with contact

Chain of Transmission Triad components

Ecological

Type of study; looks for differences between groups of people with a shared characteristic rather than individuals

Cross Sectional

Type of study; a survey, health questionnaire, “snapshot in time”

Case-Control

Type of study; Compare people with and without disease to find common exposures

Cohort

Type of study; compare people with and without exposures to see what happens in each; can be prospective or retrospective

Randomized Controlled Triad

Type of study; human experiment that randomly assigns participants to an experimental or control group

Quasi Experiments

Type of study; research similarities with traditional experimental design or RCT but lack element of random assignment to treatment/control; participants are assigned a group based on non-random criteria

(ad/bc)

Odds ratio; used in a case-control study

d

no disease no exposure

[a/(a+b)]/[c/(c+d)]

Relative Risk; used in cohort study

a

disease and exposure

b

no disease and exposure

c

disease no exposure

a/(a+b), c/(c+d)

Attack rate; the rate that a group experienced an outcome or illness equal to the number sick divided by the total in that group

sigma [(observed-expected)²/expected]

Chi-Square

Epi Curve

Histogram showing course of an outbreak by plotting the number of cases of a condition according to time of onset

Point Source

Epidemic that occurs when people are exposed to the same exposure over a limited, well defined period of time; the shape of the curve commonly rises rapidly and contains a definite peak, followed by a gradual decline

Continuous Common Source

Type of epidemic that occurs when the exposure to the source is prolonged over an extended period of time and may occur over more than one incubation period; the 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

Propagated

Epidemic that occurs 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; usually contains a series of successively larger peaks; distance between peaks indicates incubation period of disease

Intermittent Source

Type of epidemic in which people are intermittently exposed to a source; generally multiple peaks; ex: spoiled food at a store

Random Error

Result of fluctuations around a true value because of the sample population

Precision

A measure of random error that is inversely related

Systematic Error

Any error other than random error; usually consistent and repeatable and often occurs from flawed equipment or experimental design

Selection Bias

Occurs when selection of participants for a study is affected by an unknown variable that is associated with the exposure and outcome being measured

Information Bias

Occurs when bias is introduced through an error in measurement or observation

Recall Bias

When studies, some subjects may more easily recall specific habits related to a disease or condition than subjects not affected with the disease or condition

Confounding Bias

Bias resulting from mixing effects of several factors; deals with causation and not variation in study results

Agent

A microbial organism with the ability to cause disease

Reservoir

A place where agents can thrive and reproduce

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

Mode of Transmission

Method of transfer by which the organism moves or is carried from one place to another; contact, vector, and vehicle