Science Olympiad - Disease Detectives (copy)

Classical vs clinical

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Classical epidemiology

is population oriented and 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

heavily dependent on laboratory support

Chronic Disease Epidemiology

dependent on complex sampling and statistical methods

Descriptive vs analytic

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Descriptive epidemiology

considers time/place/person data on a disease to determine trends. Answers questions like who/what/where/when.

Analytic epidemiology

involves hypothesis testing to determine the cause of disease (causal relations). Answers questions like why/how.

Basic Epidemiology Terms

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Disease

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

Opportunistic disease

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

Noscomial disease

An infection that is acquired in a hospital.

Iatrogenic 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

Susceptibility

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 the 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.

Period prevalence

The total number of cases of disease in a given population over a period of 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 a high attack rate in those exposed and a low attack 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

When you may have been exposed.

Isolation

When you have been exposed.

Outbreak investigation

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The Steps of Outbreak Investigation

Depending on the source, you will find 10 or 13 steps of outbreak investigation. The following are the 13 steps:

Prepare for field work

Research the disease or situation and gather needed supplies and equipment to conduct the investigation.

Make official administrative and personal travel arrangements.

Follow protocol and contact all parties to determine roles and local contacts.

Establish the existence of an outbreak

Consider severity, potential for spread, public concern, and availability of resources.

Verify the diagnosis

Verify the procedures used to diagnose the problem and check methods used for identifying infectious and toxic chemical agents.

Be sure that the increased number of cases is not due to experimental error.

Interview several persons who became ill to gain insight concerning possible cause, source, and spread of disease or problem.

Need to screen ill persons, collect clinical and environmental samples and get them tested in order to determine agent.

Construct a working case definition

Establish with the 4 components or standard criteria for determining who has the disease or condition:Clinical information about the disease or condition

Characteristics of the affected people

Location or place

Time sequence

Identification of specific cases

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 information, clinical information, time, person, place, and risk factors.

Find cases systematically and record information

For each case, the following information should be collected: identifying information, demographic information, clinical information, risk factor information, and reporter information.

Perform descriptive epidemiology

Consider the time, place, and person of an outbreak. This can involve epi curves (time), spot maps (place), and case information (person).

Develop hypotheses

Use the agent/host/environment triad to create a hypothesis.

Evaluate hypotheses epidemiologically

Perform studies (case-control or cohort) to validate a hypothesis.

Reconsider, refine, and re-evaluate hypotheses

Use experimental data to narrow the hypothesis.

Compare and reconcile with laboratory and/or environmental studies

Laboratory evidence is necessary to confirm a hypothesis.

Implement control and prevention measures

Should be performed as soon as possible (when the source is known).

The goal of control and prevention measures is to disrupt the chain of transmission.

Initiate or maintain surveillance

Evaluate the success of control and prevention measures.

Communicate findings

Can include an oral briefing, written report, PSA, etc.

Surveillance

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Purpose of Surveillance

The purpose of surveillance is to gain knowledge of patterns of disease, injury, or other health problems in a community for prevention and control purposes. Surveillance is necessary to influence public health decisions and evaluate control measures.

Five Step Process for Surveillance

Identify, define, and measure the health problem of interest

Collect and compile data about the problem (and if possible, factors that influence it)

Analyze and interpret these data

Provide these data and their interpretation to those responsible for controlling the health problem

Monitor and periodically evaluate the usefulness and quality of surveillance to improve it for future use (surveillance of a problem often does not include actions to control the problem),

Types of surveillance

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Passive

Diseases are reported by healthcare providers. This type of surveillance, though simple and inexpensive, is often limited by incomplete reporting and quality variation in reporting

Active

Health agencies contact health provers seeking reports. This ensures more complete reporting of conditions. Active surveillance is often used with a specific epidemiological investigation or during an outbreak

Syndromic

Signs of the disease (such as school absences or prescription drug sales) are monitored as a proxy for the disease itself. The symptom must be infrequent and severe enough to warrant investigation of each identified case, and must be unique. This form of surveillance is often used when timeliness is key, diagnosis is difficult or time-consuming, or when detecting and defining the scope of an outbreak.

Sentinel

Professionals selected to represent a specific geographic area or group report health events to health agencies. This is used when high-quality data can't be obtained through passive surveillance. It involves monitoring trends or key health indicators and a limited network of reporting sites. Advantages include being able to implement intervention earlier and not being as reliant on doctors to diagnose disease. One downside to sentinel surveillance is that it's not as effective for detecting rare diseases or diseases that occur the outside the catchment areas of the sentinel sites.

Hill's Criteria for Causation

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

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 pure culture.

The cultured microorganism 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

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

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

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

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

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

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.

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

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

Modifying or preventing host response should eliminate or decrease disease.

All findings should make biological and epidemiological sense.

Types of Carriers/Vectors

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Convalescent

Humans are also capable of spreading disease following a period of illness, typically thinking themselves cured of the disease

Incubatory

When an individual transmits pathogens immediately following infection but prior to developing symptoms

Chronic

Someone who can transmit a disease for a long period of time

Genetic

has inherited a disease trait but shows no symptoms

Transient/Temporary

Someone who can transmit an infectious disease for a short amount of time

Epidemiological Triads

Epidemiologists use two triads. The first is the foundation for descriptive epidemiology - person, place and time. The second is described in the next section.

Chain of Transmission Triad

An external agent

A susceptible host for the disease

The environment where the host comes into contact with the agent

Epidemiological Studies

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Basic Studies

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Ecological

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

Cross Sectional

a survey, health questionnaire, "snapshot in time"

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. Can be prospective or retrospective.

Randomized Controlled Trial

human experiment that randomly assigns participants to an experimental or control group

Quasi Experiments

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

Advantages and Disadvantages to Study Designs

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Trial

Pros:

Most Scientifically Sound

Best Measure of Exposure

Cons:

Time Consuming

Unethical for Harmful Exposures

Most Expensive

Cohort Study

Pros:

Most Accurate Observational Study

Good Measure of Exposure

Correct Time Sequence

Good for Rare Exposures

Easy Risk Calculation

Cons:

Time Consuming

Expensive

Bad for Rare Diseases

Possible Loss of Follow-up

Case-Control Study

Pros:

Can Study Rare Diseases

Relatively Less Expensive and Relatively Fast

Good for Rare Diseases

Good for Long Latency Periods

Cons:

Possible Time-Order Confusion

Error in Recalling Exposure

Only 1 outcome

Hard to find good controls

Cross-Sectional Study

Pros:

Fastest

Least Expensive

Good for More Than 1 Outcome

Cons:

Possible Time-Order Confusion

Least Confidence in Findings

2x2 Table

A table which has two columns and rows for people with or without exposure and with or without disease; shows the number of people with each characteristic.

Odds Ratio

used in case-control study,

Relative Risk

used in cohort study

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.)

Chi-Square

used to determine the statistical significance of the difference indicated by the relative risk or odds ratio. Chi-Square compares your observed values (a, b, c, and d) with the expected values for those same groups.

Validity of Study Results: Error and Bias

Statistical bias, in the mathematical field of statistics, is a systematic tendency in which the methods used to gather data and generate statistics present an inaccurate, skewed or biased depiction of reality.

There are a total of 9 different categories of biases, and they can be found below. There are multiple sub biases in each category.

Selection Biases

Pertaining to how the participants are chosen or retained in a study. This affects the accuracy and applicability of the data.

Performance Biases

Researchers or participants alter their behavior, changing the accuracy of the data.

Measurement Biases

Biases stemming from error in data collection.

Information Biases

Biases stemming from errors in accuracy or lack of completeness in data.

Cognitive Biases

Biases stemming from subjective judgment and irrational decision-making.

Reporting Biases

Biases related to how study findings are presented or disseminated.

Systematic Biases

General errors affecting the entire study framework.