Epidemiology Spring 2017

Time characteristics: annual, seasonal, and daily or even hourly occurrence during an epidemic

Place characteristics: geographic variation, urban-rural, location of work or school

Personal Characteristics:  age, race, sex, SES, Behaviors, etc...

Descriptive: what, who, when, where

Analytic:  Why, How

• Observe
• Analyze
• Identify
• "natural experiments" in human populations

Humans will naturally conduct experiments on themselves by:

• choice
• lifestyle
• accident
• political atmosphere
• cultural beliefs

400 BC - explain disease occurrence from a rational instead of supernatural viewpoint.  He suggested environmental, host factors, and behaviors might influence the development of disease

1600's - first to quantify patterns of birth, death, and disease occurrence, noting male-female disparities, infant mortality, urban-rural differences etc..

1830's - systematically collected and analyzed britains mortality statistics.  He is considered the "Father of Modern Vital Statistics and Surveillance"

1840's - an anesthesiologist who became known as the " Father of Field Epidemiology".  His work illustrates the sequence from descriptive epi to hypotheses generation to hypothesis testing (analytic) to application (the broad street pump)

• Most commonly measured by SES, education, and occupation.
• Other ways are:
• demographics (age gender Family status SES)
• community (define what services are available also causes of death leading disease in community etc..)
• Health variables

• 1 look at history of the health of populations
• 2 diagnose the health of the community
• 3 health services and evaluation
• 4 causality in epidemiology
• 5 identification and studies

• reasonable
• individual
• population
• process
• association
• risk
• identified
• IS
• individual

origin and development of disease

• occurs after the precursors have interacted with the host
• initial appearance of disease (presymptomatic?) characterized by tissue and physiologic changes
• development of active signs and symptoms
• recovery or death

• occurs before the precursors of disease have interacted with the host
• What are precursors?
• How do they interact with host?
• symptoms?
• recovery or death?

• Primary prevention
• secondary prevention
• tertiary prevention

occurs during prepathogenesis.  Can be active or passive ie education about how have healthy eyes

occurs during pathogenesis.  Reduce progress of disease.  ie screening for disease, eye test

disease has occurred.  limit disability from disease ie glasses, rehab treatment

• primary: exercise limit salt, education
• secondary: health screenings, take blood pressure
• tertiary: medicine

number of cases being studied

number of cases in a group. cases is the numerator and group is the denominator. The cases are always part of the denominator.  Always expressed as a percent so you multiply by 100.  5 cases of sickness over 21 people in class = 0.238 times by 100 for a percent = 23.8%

There is no relationship between numerator and denominator. ie 21 people in class 1 is male and 20 are female so write it 1:20

uses a measure of time and allows comparisons of groups or populations over the same time period. Can also be comparisons among different groups in same time period.

• is the proportion of persons in a population who have a particular disease at a specified point in time (point prevalence) or over a specified period of time (period prevalence)
• all new and preexisting cases during a given time period/population during the same time period multiplied by 10 to the nth power

• is a measure of the frequency with which an event occurs in a population over a period of time.  The numerator is new cases during the specified period.  The numertor should not include cases which occurred or were diagnosed earlier.  The denominator is the population at risk.
• new cases occurring during a given time period/ population at risk during the same time period multiplied by 10 to the nth power

similar to incidence rate.  used for a well defined population observed for a limited time (you know everyone who was there like at a church party).  This rate is usually expressed as a percent so 10 to the nth power equals 100. number of new cases among population during the period/ population at risk at teh beginning of the period multiplied by 10 to the nth power

• based on the actual number of events in a population over a given time period
• Birth rate
• fertility rate

• number of live births during a time period
• live births/population

number of live births in an area during a time period divided by the number of women of child bearing age (generally 15 - 44)

• Investigator shares findings with others to create large data sets and pooling of information (called meta analysis)
• Enhances knowledge BUT primary investigator loses control

• All deaths in the US and other developed countries
• includes demographic information and cause of death
• cause of death may not be a secondary illness to the initial disease of interest
• primary cause of death may be unclear

• individual states can add diseases of local concern
• CDC maintains surveillance for diseases of interest that can spread rapidly and affect large populations or diseases of rare occurrence