3.2 - Epidemiology

epidemiology

study of the occurrence and distribution of health-related states or events in specified populations, including the study of the determinants influencing such states, and the application of the knowledge to control the health problems; study of the distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems

epidemiology greek structure

composed of 3 greek words;

-epi - upon

-demos - people

-logy - the study of something

epidemiology purposes in PH practice

1. discover - the agent, host, and environmental factors that affect health

2. determine - the relative importance of causes of illness, disability, and death

3. identify - those segments of the population that have the greatest risk from specific causes of ill health

4. evaluate

epidemiology frameworks

1. epidemiological constants

2. epidemiological triad

3. web of causality - web of causation

epidemiological constants

1. person - who

2. place - where

3. time - when / how long

epidemiological triad

considers the interrelationship of 3 elements;

1. agent

2. host

3. environment

interventions can be directed at any element

agent

part of epidemiological triad; biologic (bacteria, viruses), chemical (poison, alcohol, smoke), physical (trauma, radiation, fire), nutritional (lack, excess)

host

part of epidemiological triad; age, sex, race, genetic profile, previous diseases, immune status, religion, customs, occupation, marital status, family background

environment

part of epidemiological triad; temperature, humidity, altitude; crowding, housing, neighborhood; water, milk, food; radiation, pollution, noise

web of causation

indicates an interplay between direct and indirect causes; interventions can be directed towards any set of causes / links

causality criteria

1. strength of association

2. consistency of findings

3. biologic plausibility

4. correct temporal sequence

5. dose-response relationship

6. specificity of the association (one agent causes one disease)

7. experimental evidence

percent change

change related to a variable over time; eq: ([Time B - Time A] / Time A) x 100

rate

proportion of a disease or health-related event within a population at a certain point in time; eq: (number of deaths / population) x a constant

mortality

number of deaths within a population; eq: (number of deaths / population) x a constant

morbidity

number of people experiencing a disability, illness, or disease within a population; eq: (number of cases / population at risk for condition) x a constant

attack rate

another way to consider number of people affected; eq: (number of cases / total population) x a constant

frequency of disease

includes the number of cases of the illness / condition, the size of the population at risk, and the period during which we are calculating the rate

incidence

number of new cases of a disease or illness at a specific time or over a specific period of time; ex: total number of new cases of gonorrhea in a year

prevalence

number of accumulated cases of a disease / illness including new and existing cases at a specific time; ex: total number of people living with AIDS

reliability

precision, consistency, or repeatability of results; variation in the trait being measured; observer variation; inconsistency and stability in the instrument

validity

accuracy; measurement is measuring the intended factor; includes sensitivity and specificity

sensitivity

accuracy of test to identify persons with the condition; true positive results; measured with positive predictive value (PPV)

specificity

accuracy of a test to identify persons without the condition; true negative results; measured with the negative predictive value (NPV)

descriptive epidemiology

considers population and health data that are already available; includes the calculation of rates; provides understanding of what is happening in the population; "describes” the health, wellness, and disease in the population; helps formulate hypotheses about health

analytical epidemiology

examines health data to determine associations between risk factors and health phenomenon; conducts studies to test hypotheses; provides understanding of connections between risks and disease; “analyzed” the connections between risk and disease in the population; tests hypotheses about health

types of epidemiology studies

1. experimental

2. observational - descriptive / analytic epidemiology

studies

conducted in an attempt to discover associations between an exposure or risk factor and a health outcome and to test hypotheses about this exposure / risk factor

study designs

1. cross-sectional study

2. case-control study

3. cohort study

cross-sectional study

subjects are selected because they are members of a certain population subset at a certain time

case-control study

subjects are identified as having a disease / condition are compared to subjects without the same disease / condition; uses odds ratio

odds ratio

the odds of having a disease / condition among the exposed in comparison with the unexposed

cohort study

subjects are categorized on the basis of their exposure to one or more risk factors; uses relative risk

relative risk

measure of association comparing the incidence rate in the exposed group with the incidence rate in the non-exposed group

outbreak investigation steps

1. establishing the existence of an outbreak

2. preparing for fieldwork

3. verifying the diagnosis

4. defining and identifying cases

5. using descriptive epidemiology

6. developing hypotheses

7. evaluating the hypotheses

8. refining the hypotheses

9. implementing control and prevention measures

10. communicating findings