Types of Studies
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Descriptive: exploratory analysis, studying rare or new diseases, covers person place and
time.(who what where)
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Time: describing the occurrence of a disease based on time(long term trends,seasonality,
week time and day, epidemic period using epi-curve)
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Place: describing the occurrence of a disease based on place, provides with geographic
extent of problem
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Person: describing occurrence of disease by personal characteristics, age is most important,
followed by sex, race and socioeconomic status.
Analytic: Identify and quantify the relationship between an exposure and a health outcome (how
and why)
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Experimental: Investigator finds exposure for each individual or community and tracks to
detect the effects of exposure on each individual or community
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Observational: simply observes the exposure and disease status of each individual
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Case-control(most used): compares previous exposures between individuals with
disease and individuals without disease (control group). Control group is the expected
amount of exposure in that population
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Cross-sectional: individuals are measured by their exposure and health outcome. Is
often suggested as the weakest study
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Cohort(most used): record whether individuals are exposed and track each individual to
see if they develop disease
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Prospective: Following information from the future
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Retrospective: Surveying information from the past
Ecological: Groups of people are used as 1 single or unit observation
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Case definition
1.
2.
3.
4.
Clinical information - about the disease or condition
Characteristics - of the affected people
a.
Key characteristics of affected people(age, race, sex, occupation, exclusions criteria)
persons with no history of disease X
Location or place - as specific as possible as restaurant, country, or several specific areas
a.
Specific geographic location or facility
Time sequence - specific time during which the outbreak or condition occurred
a.
Time period associated with the illness
Surveillance
● The ongoing and systematic collection analysis and interpretation of health data in the
process of describing and monitoring a health event.
● Steps: Data Collection, Data Analysis, Data Interpretation, Data Dissemination, Link to action
● Passive Surveillance: diseases reported by health care professionals as reporting cases of
measles.
● Active surveillance: health agencies contact health care providers seeking reports as
searching for other cases of measles to identify potential outbreak.
● Sentinel surveillance: involves only a limited network of carefully selected reporting sites
targeting a particular disease
● Syndromic surveillance: focuses on one or more symptoms to detect or anticipate outbreaks
as influenza causing symptoms and absentee increases.
Disease Detectives Scientific Method
1.
Obtain background information
2.
Define problem
3.
Formulate hypothesis
4.
Develop a study to test hypothesis
5.
Cellect data and observations
6.
Evaluate results
7.
Determine if hypothesis is correct/modify
8.
Formulate conclusions
9.
Report results
Confirmed –must have diagnosis with case definition plus lab verification
Probable – many factors point to diagnosis may not have lab verification
Possible – some factors point to diagnosis
Key Terms
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Outbreak- a sudden rise in the number of cases of a disease the sudden or violent start of
something unwelcome, when more cases are there than expected
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Epidemic- sudden disease outbreak
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Pandemic- spread of a disease in country/worldwide
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Sporadic- a disease that randomly occurs, no pattern to its occurrence
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Vector- an organism that can carry disease
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Cluster- lots of cases of the same disease all at the same time
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Epidemiologic- relating to the branch of medicine which deals with the incidence, distribution,
and control of diseases and the study of what is upon people
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Epidemic curve-the graph we use in epidemiology
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Severity-seriousness,how terminal is the disease, how bad does it affect the susceptible
host.
CHAIN OF INFECTION●
Infectious agents- prions,parasites, fungi, bacteria
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Reservoirs ( how they stay alive)- food, water, people
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Portals of exit(how they leave the reservoir)- blood, poop/feces/excretion,secretion,skin
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Modes of transmission- direct contact, droplets,vectors, vehicle(food), airborne
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Portals of entrance- cuts, skin, mucus
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Susceptible host- who has disease, new sick person
Formulas
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Odds ratio-(a*d)/(b*c). Interpret- if the odds ratio is higher than 1.0 than that risk is a potential
risk factor.
Relative risk-(a/a-b)/(c/c+d). If the relative risk is 1 than there is no difference higher than 1
than the event is more likely to occur with exposure, lower than 1, the event is less likely to
occur with exposure
Attack rate- how many people are affected by the disease per 100 we use percentages.
Incidence rate - num of new cases/population
Public Health Approach
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The focus of public health is on the health, safety, and well-being of entire populations.
Steps: Surveillance, Risk Factor Identification, Intervention Evaluation, and Implementation.
What determines the health of a population, Societal characteristics, genes and biology,
health behaviors, medical care.
Extra - John Snow was the father of epidemiology
Steps in outbreak identification
1.
Collect data – surveillance
2.
Assessment – inference
3.
Hypothesis testing – how and why
4.
Action – intervention
Agent: is what causes the disease, is a microbe
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Bacteria
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Single celled organism, can reproduce by themselves, filled with fluid and have
threadlike structures to move themselves
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Virus
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May have a spiny outside layer, have a core of genetic material, cannot
reproduce on its own, they infect cells and take over the cells reproductive
machinery
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Fungi
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Are plants made up of many cells, need living matter to reproduce
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Protozoa
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Very small and live in water, they are parasites and live of other living beings
Host: are who is exposed and harbors the disease
Environment: is the favorable surrounding to the hosts