Shared Flashcard Set

Details

Lecture 4: Applied Public Health Epidemiology
04 Epi Outbreak - FIXED
62
Health Care
Graduate
12/12/2011

Additional Health Care Flashcards

 


 

Cards

Term
Epidemiology Top Ten
Definition
1. Epidemiology is the study of how disease is distributed in populations and the factors that influence or determine the distribution. 2. Disease is not distributed randomly: there are measureable factors that influence the patterns and causes of disease in a population. 3. Disease causation is multifactorial: many factors work together to create an environment in which disease occurs, and identifying and measuring the relative contribution of these factors is a central focus of epidemiology. 4. epidemiology is about population-level (vs. individual) patterns of disease. 5. epidemiology is done by studying samples of larger populations: much of epi's statistical toolkit is focused on drawing inferences from samples back to populations. 6. measurement (of disease states, exposure, populations) is central to the practice of epidemiology. 7. epidemiology is fundamentally about comparisons across time, space, social groups, disease conditions, etc. 8. descriptive epidemiology is the study of the amount and distribution of disease within a population: tools are surveillance and vital statistics, with ongoing data collection often a component, and are conducted mainly by federal, state, and health agencies. 9. analytic epidemiology is the study of determinants of disease or reasons for relatively high or low frequency in specific groups: tools are focused investigations, data collection is to test a hypothesis, and is conducted by health agencies and academic researchers. 10. Incidence is the number of new cases of a disease among those at risk for developing the disease during a specified time period; prevalence is the number of cases present in the population at a specified time.
Term
Epidemiology (def.)
Definition
The study of how disease is distributed in populations and the factors that influence or determine this distribution.
Term
Disease distribution
Definition
Disease is not randomly distributed: There are measureable factors that influence the patterns and causes of disease in a population.
Term
Multifactorial disease causation
Definition
A multitude of factors conspire to create an environment in which disease occurs. Identifying and measuring the relative contribution of these factors is a central focus of epidemiology.
Term

Population-level

 

Definition
Epidemiology is about population-level (vs. individual) patterns of disease
Term
Sampling
Definition
Epidemiology is done by studying samples of larger populations, and much of the statistical toolkit of epidemiology is focused on drawing inferences from samples back to populations.
Term
Measurement
Definition
Measurement of disease states, exposure, populations, is central to the practice of epidemiology.
Term
Comparisons
Definition
Epidemiology is fundamentally about comparisons across time, space, social groups, disease conditions.
Term
Descriptive Epidemiology
Definition

The study of the amount and distribution of disease within a population.

Tools: surveillance, vital statistics

Data are often collected on an ongoing basis

Conducted mainly by federal, state, and local health agencies

Term
Analytic Epidemiology
Definition

The study of determinants of disease or reasons for relatively high or low frequency in specific groups.

Tools: focused investigations

Data collected to test a hypothesis

Conducted by health agencies and academic researchers

Term
Incidence
Definition

# of new cases of a disease

# at risk of developing the disease

 

during a specified time period

Term
Prevalence
Definition

# of cases present

# in the population


at a specified time

Term
Population
Definition
a group of people with a common characteristic; can be dynamic or fixed
Term
Dynamic population
Definition
Members may join or leave through birth, death, immigration, emigration, initiation or excommunication
Term
Fixed population
Definition

A population that cannot accept new members and for whihc members cannot become non-members

 

Term
Population at Risk
Definition

Defined population in which all members are biologically capable of developing the disease (susceptible to disease with a non-zero risk of developing the disease, not a high-risk of developing the disease).

 

Whether a person is at risk for the disease may change over time, with short vs. long-term differences in risk status

Term
Reasons for a person not being at risk for a disease
Definition

Already has the disease

 

Not biologically capable of getting the disease (a woman is not at risk for getting prostate cancer)

 

has acquired immunity

Term
Population at Risk for a Recurrent Disease and Non-recurrent Disease (flowcharts)
Definition

susceptible / at risk --> diseased --> susceptible / at-risk

 

vs.

 

susceptible / at-risk --> diseased

or

susceptible / at-risk --> diseased --> immune

Term
Natural History of Disease
Definition

Course of a disease from onset to resolution (Last, 1995)

 

 

Course of progression if no medical intervention is taken and disease is allowed to run its full course (Timmreck, 1998).

Term
Models of Disease Causation
Definition

Proposed models to organize our thinking about multiple causes of disease:

The Epidemiological Triangle

The Wheel Model

Web of Causation

Chinese Boxes

Term
Epidemiological Triangle
Definition

Implies that the agent, host and environment must each be analyzed to understand patterns of disease

 

Environment, agent, and host at the corners of triangle

Time is in the center

 

Example: Legionnaire's Disease

Environment: aqueous reservoir

Agent: legionellae bacilli

Host: susceptible host (age, smoking, diabetes, lung disease)

Time!

Term
Wheel Model
Definition

Implies multiple etiologic factors

Recognition of genetic susceptibility

 

The genetic core is surrounded by the social environment, biologic environment, and physical environment.

 

Example: HIV Infection

Genetic core: genetic variants in CCR5 and other genes

Social Environment: Culture of IV Drug Use

Biologic Environment: HIV Strain

Physical Environment: Contaminated Needles

Term
Web of Causation
Definition

Effects develop as a result of chains of causation.

Each link is the result of a complex geneaology of antecedents.

 

Example: Breast Cancer

Term
Chinese Boxes
Definition

Set of boxes graduated in size so that each fits into the next larger one. Integrates factors at many levels of organization: micro-level, individual-level, and macro-level causes.

 

Example: Obesity

Micro-level causes: genetic differences in leptin, leptin receptors, satiety, tolerance for high intensity exercise.

Individual-level causes: eating and energy expenditure choices.

Macro-level causes: obesogenic environment with plentiful inexpensive, fat and caloric dense foods and physical exertion engineered out of our daily lives.

Term
Outbreak Investigation: Key Steps
Definition

1. Define the outbreak and validate its existence

2. examine the distribution of cases by time and place

3. look for combinations/interactions of relevant variables

4. develop hypotheses

5. test hypotheses

6. recommend control measures

7. compile findings

8. disseminate findings for future learning

Term
endemic
Definition
the habitual or usual presence of a disease within a given geographic area
Term
epidemic
Definition
occurrence of disease clearly in excess of normal expectancy
Term
pandemic
Definition
worldwide pandemic (eg influenza of 1918)
Term
outbreak recognition
Definition

are there more cases of a known disease than would normally be expected?

pandemic

epidemic

pandemic

Term
Step 1. Define Outbreak and Validate Existence
Definition
A. establish case definition: the specific operational definition of who "counts" as having the disease
B. define the population at risk
C. Do observed cases exceed the expected number?
D. Calculate the attack rate: # cases among PAR / PAR
Term
Case Definition factors
Definition
time and space criteria
pathogen-specific: culture results, PCR, serology
syndrome-specific: clinical criteria, exclusion criteria
strict case definition preferred to increase specificity and minimize false positives
Term
Attack Rate
Definition
# cases among population at risk /
population at risk
Term
Step 2: Examine distribution of cases over time & place
Definition
Epidemic curve
Term
3. Look for combinations of relevant studies
Definition
Term
4. Generate hypotheses
Definition
-Microbiology, descriptive epidemiology, previous experience provide clues to possible source and root exposure. For example, which mode of transmission was likely given disease characteristics?
-Open-ended interviews with a subset of cases can help identify all relevant exposures.
Term
Modes of transmission
Definition
Droplet contact: coughing, sneezing on another person
Direct physical contact: touching an infected person, including sexual contact
Indirect contact: usually by touching a contaminated surface
Airborne transmission: if the microorganism can remain in the air for long periods
Fecal-oral transmission: usually from contaminated food or water sources
Vector-borne transmission: carried by insects or other animals.
Term
Step 5: Test hypotheses
Definition
conduct a study designed to test a hypothesis. The study design is based on study questions, resources, and target populations. The intent is to determine whether given exposure led the occurrence of the disease. Two typical study designs include retrospective cohort and a case-control
Term
Two typical study designs for an outbreak investigation
Definition
Retrospective cohort: individuals selected based on exposure
Case-control: individuals selected based on disease status
Term
Retrospective cohort study
Definition
individuals are selected for participation based on exposure
Term
Case-control study
Definition
Individuals are selected for participation based on disease status
Term
Relative Risk in a Cohort Study
Definition
what is the ratio of the risk of disease in exposed individuals to the risk of disease in non-exposed individuals?

Risk of Incidence in the exposed / risk of incidence in the unexposed

This can be calculated for a COHORT STUDY
Term
Interpreting Relative Risk (RR)
Definition
RR = 1 ... the risk in the exposed population is equal to the risk in the non-exposed population; there is no association.

RR>1 ... The risk in the exposed population is greater than the risk in the non-exposed population; a positive association which is possibly causal

RR<1... the risk in the exposed population is less than the risk in the non-exposed population; a negative association and a possibly protective relationship.
Term
RR =1
Definition
risk in exposed = risk in nonexposed
no association
Term
RR>1
Definition
risk in exposed > risk in non-exposed

positive association

possibly causal
Term
RR < 1
Definition
risk in exposed < risk in non-exposed

negative association

possibly protective
Term
Odds
Definition
probability that an event will happen / probability that an event will not happen
Term
odds
Definition
= P / ( 1 - P ) where P = probability

Example: probability that the Phillies win tonight is 0.33; the odds that the Phillies win tonight is 0.33 / ( 1 - 0.33 ) = 0.33 / 0.67 = 0.5 = 2 to 1 against
Term
Calculating Odds Ratio in a Cohort Study
Definition
Odds ratio = odds that an exposed person gets sick / odds that an unexposed person gets sick

= (exposed sick / exposed not sick) / (unexposed sick / unexposed not sick) = exposed sick x unexposed not sick / exposed not sick x unexposed sick = odds ratio
Term
Interpreting odds ratios in cohort studies
Definition
OR = 1...risk in exposed = risk in nonexposed (no association)

OR>1... risk in exposed > risk in nonexposed (positive association, possibly causal)

OR<1...risk in exposed
Term
OR = 1
Definition
risk in exposed is equal to risk in nonexposed

no association
Term
OR > 1
Definition
risk in exposed is greater than the risk in the nonexposed

positive association

possibly causal
Term
OR < 1
Definition
risk in exposed < risk in non-exposed

negative association

possibly protective
Term
Calculating an odds ratio in a case-control study
Definition
odds ratio = odds that a case was exposed / odds that a control was exposed = exposed cases/unexposed cases / exposed controls/unexposed controls
Term
Odds ratios in cohort vs. case-control studies
Definition
Cohort studies: odds ratio is the odds that an exposed person gets sick / odds that an unexposed person gets sick. For a cohort study you CAN calculate incidence and RR.

Case-control study: odds that a case was exposed / odds that a control was exposed
Term
Step 6: Recommend control measures
Step 7: Compile Findings
Step 8: Disseminate findings for future learning.
Definition
Term
Sensitivity
Definition
Proportion of true cases correctly identified as cases or positives

High sensitivity = few false negatives

sensitivity = true positives / (true positives + false negatives)

= number of cases that are correctly identified as having the disease / sum of true positives and the number of cases that are identified as not having the disease.
Term
specificity
Definition
proportion of true non-cases correctly identified as negatives

high specificity = few false positives

specificity = true negatives / true negatives + false positives
Term
case definition in a food borne illness outbreak
Definition
With outbreaks of food-borne illness, two critical parts of an epidemiologic investigation are the specific case definition and the specifically defined sources of exposure.
Term
importance of specific case definition and defined exposure sources
Definition
because an outbreak implies a common source, a specific case definition can increase the efficiency of the investigation by excluding unrelated cases that would dilute estimates of association. Specific exposure information including details on source is a critical part of epidemiologic analysis that needs to be collected up front.
Term
food safety = surveillance + epidemiology + speed
Definition
good surveillance improves sensitivity of outbreak detection

rigorous epidemiology improves specificity of outbreak investigation (case definitions and exposure source)

speed improves outbreak containment, reduces harm, and maintains public confidence
Term
outbreaks must be conducted rapidly to help identify contaminated products and remove them from the marketplace
Definition
standard practice:
-confirm diagnosis
-establish existence of outbreak
-hypothesis generating interviews
-case-control study to test hypothesis
-trace source of implicated food product

speed it up
-accelerate investigations by combining features of hypothesis generating interviews, case control studies, and source traceback
-provide rapid response interview teams to support local investigations
-increase efficiency by moving information, not people
Term
Comparison of when to use a case control or a cohort study
Definition
A case control study is best when the population at risk is not known, when the disease is rare, when exposure is common, and when time from exposure to disease development is long. Cases and controls can be identified from the population, and exposure can be determined for each group. The direction of inquiry is backwards in time.

A Cohort Study is best when the disease occurs in a well-defined group, the disease is common among the exposed, and the time from exposure to disease is short. A sample without the health population is obtained from the general population, then exposures are compared to emergence of the health problem. The cohort study can be prospective or retrospective.
Supporting users have an ad free experience!