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HLTH 240b (10)
Lecture 3

HLTH 240b Lecture 3: Case Definitions

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Global Health Studies
HLTH 240b
Marney White

HLTH 240: Epidemiology and Public Health 1/24/17  Stats vs. epidemiology 1. Descriptive stats: mean median mode a. Vs. analytic: testing 2. Descriptive epidemiology: describing shape of epi event and identifying patterns a. Rate of transmission b. Demographic/geographic variations c. Includes descriptive stats that provide info on disease patterns by various characteristics of person, place, time 3. Descriptive stats: a. Providing clues about disease causation and prevention that are usually investigated further in formal studies b. Assessing health status of a population c. Allocating resources efficiently targeting populations for education or preventive programs d. Routinely collected data from many sources including data of mortality and natality from vital records, reportable diseases from surveillance programs, other diseases from national surveys e. Many now available on internet o NHANES o BRFSS o SEER  Case definition 1. Case: individual with the disease a. Precise operational definition used to categorize cases b. Often includes probable or suspected cases c. Consideration: case definitions may change over time o E.g. development of lab tests 2. Clinical presentation 3. Clinical criteria a. Lab tests b. Symptoms (subjective) c. Signs (objective physical findings) d. May be polythetic format e. Case confirmation may depend on response to treatment o May specify limits on time, place, person  E.g. may require persistence of X symptoms for Y amount of time 4. Gradations a. Confirmed case b. Probable case c. Possible case d. Suspected case e. Not a case f. Example: congenital syphilis o Chronic infection cause by bacterium o Risk of transplacental infection of fetus g. Changing definitions over time by CDC o Diagnostic criteria becomes more defined and precise o Causes epidemic curve to increase sharply after case definition introduced.  Prior to change in definition many cases went underdiagnosed.  Primary and secondary diagnoses did not increase proportionally to increase in congenital syphilis.  Causes: changing criteria coupled with epidemic among pregnant woman  Epidemic attributed to crack cocaine 5. Outbreak: increase in frequency of disease above what is expected in given population a. But: apparent changes in disease frequency can be due to o Change in case definition or local recording procedures o Increased interest leading to greater scrutiny by health care workers OR increase in requests for testing by patients o Improvements in diagnostic or screening procedures  Descriptive definitions 1. Count: frequency of cases a. Simple count does not provide much info b. Who, what, when, where, how o Person: who has disease?
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