General Principles of EPI Flashcards
Describe EPI
Study of the
Frequency
distribution
cause
control of disease in populations
Understand the relationship between host, environment and organism
Purpose of EPI
Person, place, and natural history
Define Risk
Probability or likelihood of an event occuring
Define Risk Factor
Characteristic, behavior, experience that increases the probability of developing a negative health status (disease or infection).
Epidemiology, unlike clinical medicine, is population based and is useful for describing health-related phenomena in groups of people.
Epi triangle model of disease causation
Host: human or other animal
Environment: external factors associated with the host
Agent: bacteria, virus, fungus, protozoan, helminth or prion
Wheel model
Hub: host or human with an inner core of genetic information.
Surrounding environment divided into three parts: social, biological, physical.
Web Model of causation
aims to capture the more complex interactions between biological (host), environmental, and social factors contributing to disease.
Emphasizes social and political aspects of human life.
What is an association and the three types?
As one variable changes there is a resultant change in the quantity or quality of another variable.
Artifactual (spurious) (chance or random error)- may be result of study design-> systematic error or bias.
Indirect or noncausal-> may result from mixing of effects between the exposure, the disease, and a third factor (confounding variable)
Casual
What is a confounding variable?
Related to both the potential cause of a disease and the disease itself.
Scientific criteria for CAUSATION (Koch) 4 points
- organism must always be found with the disease, in accordance with the clinical stage observed
- the organism must then be grown in pure culture from a diseased host
- the same disease must be reproduced when a healthy susceptible host is innoculated
- the organism must be recovered from the experimentally infected host.
Hill’s Criteria for Caustion
Applying the criteria for causality is not as straightforward when the etiology is not clear
- Strength of association
- Consistency
- Specificity
- Temporality
- Biological Gradient
- Biologically Plausible
- Coherence
- Experimental Knowledge
- Analogy
HAI prevention strategies are wide ranging and depend on the disease in question and what information is available to the practitioner.
Primary, secondary and tertiary prevention
Primary prevention strategies to prevent the occurrence of disease include: barrier precautions, immunizations of HCP, cleaning, sterilizing, and disinfecting.
Define incidence
Number of new cases of a given disease in a given time period
Define prevalence
number of existent cases of a given disease at a given time.
Endemic
usual incidence of a given disease within a geographical area during a specified time period
Epidemic
an excess over the expected incidence within a geographical area during a specified time period
Pandemic
Epidemic spread over a wide geographic area, across countries or continents
Outbreak
A group of people with the same disease who are epidemiologically linked
Cluster
a group of persons with a given disease occurring in the same space and time, but which have not been epidemiologically linked. If linked, by EPI may become an outbreak.
Zoonosis
A disease transmitted from animals to humans
Enzootic
Usual presence of disease among animals within a geographical area. Animals may serve as a reservoir.
Epizootic
excess of disease than in expected in the animal population
Reservoir
Place where agent can survive but may or may not reproduce.
Eg. Pseudomonas (gram negative, arerobic rod) in nebulizers
Hep b on surface of hemodialysis machine
Fomite
inanimate object on which organisms may exist for some period of time
Herd immunity
resistance of a group to invasion and to spread of infectious agent
Convalescent carriers
those who have recovered from the disease but still have organisms present that can be transmitted.
Eg. a patient with cholera may continue to shed bacteria in the stool for several weeks after diarrhea has subsided.
Natural barriers to the entry of organisms include:
- skin and mucous membranes
- cilia of respiratory tract and cough mechanism
- gastric acid
- mechanical flushing - genitourinary tract
- tear flushing- protect the eye
- good nutritional status
Host factors influencing susceptibility include:
Age, sex, ethnicity, SES, martial status, lifestyle, heredity, nutritional status, occupation, immunization status, diagnostic/therapeutic procedures, Medications, pregnancy, trauma
Describe prospective or cohort studies
A group of subjects with a known exposure status for the risk factor of interest are followed over time to determine which of the subjects develops disease.
Subjects form a cohort going through time together.
Describe Case control- or retrospective
Moving backward from disease state to risk factor. identify those with disease then measure degree of exposure to the risk factor of interest.
Pros and cons of case control
Pros
data is already available. Researcher doesn’t have to wait for disease to develop- takes less time. Tend to be less expensive.
Cons
dependent on completeness of records, may be difficult to select an appropriate control group. Subject or recall bias- rely on memory of subjects.
Pros and cons of Cohort
Pros
Considered to have fewer bias- avoid subjectivity involved in collecting after the fact exposure data.
Yield incidence rates- can yield associations between risk factors and disease that were not anticipated.
Tend to carry more weight
Cons
May require lengthy follow up- more expensive. Must wait for sufficient number to develop disease. May have people drop out.
Recognizing outcome related events:
decreased rates of infection, length of stay, days in ICU,
Histogram
graphic of frequency distribution in which one bar is used for each time interval, and there is no space between the intervals
Frequency polygon
provides same info as a histogram
A CHART is a method of illustrating info using only one coordinate. They compare magnitudes of different events and to compare parts of a total picture.
Types of charts include:
Bar charts, pictograms, geographical coordinate charts, and pie charts.
Bar charts and pictograms
Used to compare magnitudes, show frequency distributions, and time-series data.
Geographical Coordinate Charts
Represent the occurrence of events using maps.
Pie charts
a pie chart is not appropriate when there are may wedges- limit the number to five or six.
U-Charts: Provide statistical process control (SPC) information to help monitor quality assurance and are most often used for monitoring length of stay and infection rates.
Provides a range of expected variation about a mean (centerline) and the upper and lower limits beyond which the process is considered out of control.
Useful in conveying changes in rates over time and identifying points in time when infection rates or other processes are outside the expected range.
In can include more than one error (infection) per patient. May be less stable with small denominators.
