Module 2: Fundamentals of Epidemiology

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