Post on 24-Feb-2016
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Module 2:Fundamentals of Epidemiology
Developed through the APTR Initiative to Enhance Prevention and Population Health Education in collaboration with the Brody School of Medicine at East Carolina University with funding from the Centers for Disease Control and Prevention
Measuring Health and Disease
Acknowledgments
APTR wishes to acknowledge the following individuals that developed this module:
Kristina Simeonsson, MD, MSPHDepartment of Public HealthBrody School of Medicine at East Carolina University
Jeffrey Bethel, PhDDepartment of Public HealthBrody School of Medicine at East Carolina University
This education module is made possible through the Centers for Disease Control and Prevention (CDC) and the Association for Prevention Teaching and Research (APTR) Cooperative Agreement, No. 5U50CD300860. The module represents the opinions of the author(s) and does not necessarily represent the views of the Centers for Disease Control and Prevention or the Association for Prevention Teaching and Research.
Presentation Objectives
Define epidemiology and recognize some of its uses Interpret distribution of disease according to person,
place, and time Calculate measures of disease occurrence and
severity
What is epidemiology, really?
Study of health and disease among populations
Basic science of public health What causes disease? How does disease spread? What prevents disease? How to control disease?
Uses of Epidemiology
Identify etiology and risk factors
Determine the extent of disease in a population
Study natural history and prognosis
Evaluate existing and new preventive and therapeutic measures/modes of healthcare delivery
Provide foundation for developing public policy and regulatory decisions
Epidemiology
The study of the distribution and determinants of diseases or other health-related outcomes in populations and the application of this study to control health problems
Distribution of Disease
Analysis of disease patterns Person Place Time
Acute Hepatitis BPerson
Source: National Notifiable Diseases Surveillance System, 2006.
Acute Hepatitis BPlace
Source: National Notifiable Diseases Surveillance System, 2007.
Incidence of acute hepatitis B, by county—United States, 2007
Acute Hepatitis BTime
Measures of Morbidity and Mortality Counts Proportions
Prevalence Rates
Incidence Attack rate Mortality rate Case fatality rate Infant mortality rate
Counts
Measure of disease frequency Number of cases or other health outcome being
studied
CholeraNumber of reported cases, 2008
CDC, MMWR Summary of Notifiable Diseases, US 2008
Prevalence
Answers the question: How common is it? Burden of disease in a population
A slice through the population at a point in time at which it is determined who has the disease and who does not
Often stated as a percentage (i.e. per 100)
Prevalence
# of cases of a disease present in the population at a specified time
# of persons in the population at that specified time
Prevalence
Don’t know when disease developed or the duration Numerator is a mix of people with different
durations of disease Do not have a measure of risk
Prevalence is appropriate measure of the burden of a relatively stable chronic condition Diabetes Hypertension
Useful for allocating health resources
1999
2009
1990
No Data <10% 10%–14% 15%–19% 20%–24% 25%–29% ≥30%
Obesity Trends*Among US Adults(*BMI≥30, or about 30 lbs. overweight for 5’4” person)
CDC, BRFSS, 1990, 1999, 2009
1999
2009
1994
Age-adjusted Percentage of U.S. Adults who had Diagnosed Diabetes
CDC’s Division of Diabetes Translation. National Diabetes Surveillance System
Incidence
Measures change from non-disease to disease Can provide a measure of risk
Also known as incidence rate
Often stated per 100,000 population per year
# of new cases of a disease during a specified period of
time
Incidence
Total number of people at risk during that period of
time
Incidence
Department of Health and Human Services, Centers for Disease Control and Prevention, and National Cancer Institute, 2010
Incidence
Department of Health and Human Services, Centers for Disease Control and Prevention, and National Cancer Institute, 2010
Incidence
Monitor changes over time Comparisons between groups
Age-specific rates Sex-specific rates
Goal setting Healthy People 2020 Objectives
Attack Rate
Similar to incidence (rate) Used when nature of the disease is such that
population is observed for a short time period, often as a result of specific exposure Foodborne outbreaks
Compares the risk of disease in groups with different exposures
Attack Rate
# of people who ate potato salad who developed gastroenteritis
Total # of people who ate potato salad
Relationship Between Incidence and Prevalence Prevalence = incidence x duration of disease
An increased prevalence may reflect Increased risk of disease in the population
▪ Increased incidence Increased duration of illness
▪ Fewer deaths from the disease (increased survival)▪ Fewer responses to treatment
Relationship Between Incidence and Prevalence An increased prevalence may reflect
Increased risk of disease in the population▪ Increased incidence
An increased prevalence may also reflect Increased duration of illness
▪ Fewer deaths from the disease (increased survival)
▪ Fewer responses to treatment
Relationship between Incidence and Prevalence
Relationship between Incidence and Prevalence
Relationship between Incidence and Prevalence
Relationship between Incidence and Prevalence
AIDS Incidence, Deaths, and Prevalence
Measures of Mortality
Mortality Rate Case Fatality Rate Infant Mortality Rate
Mortality Rate
# of all deaths in one year
# persons in the population at midyear
Case Fatality Rate
# of persons dying during a specified period after disease onset or
diagnosis
Total # of people with the specified disease
Case Fatality Rate for Avian Influenza A/H5N1
309 deaths from H5N1
522 cases of H5N1CFR 59%
WHO website, accessed 2/25/2011
Mortality Rate versus Case Fatality Rate
0% 20% 40% 60% 80% 100%
TB
Measles
Rabies
Inapparent Mild Moderate Severe Fatal
Mausner & Kramer, 1985
National Cancer Institute; A Snapshot of Pancreatic Cancer
Infant Mortality Rate
# of deaths under one year of age during a specified time interval
# of live births reported during the same time period
Expressed per 1,000
Summary
Epidemiology is the basic science of public health
Count, describe, divide, compare Must use rates to compare groups and assess risk
Primary measures of disease occurrence Incidence Prevalence
Primary measure of disease severity Case fatality rate
Collaborating Institutions
Center for Public Health Continuing EducationUniversity at Albany School of Public Health
Department of Community & Family MedicineDuke University School of Medicine
Advisory Committee
Mike Barry, CAELorrie Basnight, MDNancy Bennett, MD, MSRuth Gaare Bernheim, JD, MPHAmber Berrian, MPHJames Cawley, MPH, PA-CJack Dillenberg, DDS, MPHKristine Gebbie, RN, DrPHAsim Jani, MD, MPH, FACP
Denise Koo, MD, MPHSuzanne Lazorick, MD, MPHRika Maeshiro, MD, MPHDan Mareck, MDSteve McCurdy, MD, MPHSusan M. Meyer, PhDSallie Rixey, MD, MEdNawraz Shawir, MBBS
APTR
Sharon Hull, MD, MPHPresident
Allison L. LewisExecutive Director
O. Kent Nordvig, MEdProject Representative