EPIDEMIOLOGY

Catherine T. Horat RN MSN CS C-FNP

NUR 410 Community Focused Nursing

Epidemiology

• Definition– “The study of the distribution and

determinants of health-related states or events in specific populations, and the application of this study to control of health problems”

Last, 2001, p. 62

Epidemiology

• Studies

Epidemiology

• Epidemiologic Methods used in– Health services research– Investigate associations between– To what extent Healthy People 2000 goals

accomplished– Monitor progress of Healthy People 2010

Study of Distribution

• Distribution – Patterns of events– Influences on– Characterized as

Descriptive Epidemiology

• Based on distribution or patterns of health events in populations

• Attempts to describe a disease entry according to – Person– Place– Time

Study of Determinants

• Determinants of health – events or factors that determine or influence the patterns of

• Questions asked

Study of Determinants

• Include

Analytic Epidemiology

• Investigation of causes and association

• Directed toward understanding the etiology or origins and causal factors of a disease

• Useful for– Guiding or evaluating policies and programs

that improve the health of a community

Comparison of Analytic/Descriptive Epidemiology

• Analytic studies rely on descriptive comparisons

• Descriptive comparisons shed light on determinants

Epidemiology

• Study of populations in order to

Key Terms

• Surveillance

• Endemic

• Epidemic

• Pandemic

Epidemiological Investigational Models

• Epidemiological Triangle

• Web of Causation

• Person-Place-Time

Epidemiological Triangle

Agent

Host Environment

Epidemiological Triangle AGENT

• Causative factor contributing to health problems that must be present or lacking

Epidemiological Triangle HOST

• A susceptible human or animal who harbors and supports a disease causing agent

• Intrinsic

Epidemiological Triangle ENVIRONMENT

• All factors internal or external to a client that constitute the context in which the client lives and that influences and are influenced by the host and agent-host interactions

Web of Causation

• Web of Causation– Complex interrelationships of numerous factors

interacting to increase or decrease risk of disease

• The determination based on EVIDENCE or REASONING process that an event or state Resulted FROM or was CAUSED BY some other events, exposure, characteristics, or a combination of them (Causality)

Causality

• Criteria

Person-Place-Time

• Examines the characteristics of– People affected– The place or location– Time period involved

• Considered as variables– Person who is affected– Place where affected– Time when affected

Health Promotion and Disease Prevention

• Natural History of Disease the course of progression of a disease from onset to resolution– Prepathogenesis period (Environment)

• Disease has not developed but interactions are occurring between host, agent and environment that produce disease stimulus and increase the host’s potential for disease

– Pathogenesis period (Human)• Begins when disease-producing stimuli start to produce

changes in the tissues of humans

Natural History and Levels of Prevention

• Primary Prevention– Prepathogenesis

– Adaptation• Adaptive processes are initiated

Natural History and Levels of Prevention

• Secondary Prevention– Pathogenesis

– Discernable early lesions• Clinical recognition• Early DX and prompt treatment

Natural History and Levels of Prevention

• Tertiary Prevention treatment to arrest disease or rehabilitation– Clinical Disease

Mortality Rates

• Relative death rate

• Sum of deaths in a given population at a given time– Crude mortality rate – Cause-specific mortality rate– Case fatality rate– Age-specific death rate– Proportional Mortality Ratio

Mortality Rates

• Crude mortality rate includes • based per on 100,000 population

– #deaths in a year______ Average midyear population

• Ex– # 10,000deaths in St. Petersburg, Fl in 2002 X

100,000

# 350,000of persons in St. Petersburg Fl in July

1, 2002

Mortality Rates

• Cause-specific actual cause of deaths desired to be measured

• per 100,000

• EX#75 of men who died from pneumonia in St. Petersburg Fl in 2003

X100,000

# 60,000 of men in total population of St. Petersburg, FL, 2003

Mortality Rates

• Case-fatality– #deaths due to a specific disease X100

cases

# cases of specific disease

• EX

25 deaths from E-coli X 100 cases

300 cases of E-coli

Mortality Rates

• Age-specific– Enables comparing populations in different locations

• EX# 120 deaths among 45 year olds in Denver CO in 2005 X

100000

# 10,000 of 45 year old people in Denver CO July 1

Mortality Rates

• Proportional

• Compares number of deaths from a particular cause with deaths from all other causes

# deaths from specific cause in a specified time period X 100

Total # deaths in same time period

# 200 of Cancer deaths in 2001 X 100

# 5000 of total deaths from all causes in 2001

Morbidity Rates

• Relative incidence of disease – Incidence– Prevalence

Morbidity Rates

• Incidence– Rates that measure ALL NEW CASES arising in a

population during a defined period of time, usually 1 year

# of new cases in place during time of observation X K

Population in place at midpoint of time

60 new mump cases from 1/07 to 1/08 X 100,000

50,000 population

• K = unit of population

Morbidity Rates

• Prevalence measures total number of persons with a characteristic with the total number in the population

• 50 people with chicken pox X K

1000 people in population