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Introduction to Epidemiology

Dr. Salman Alzayani, MD, MSc, PhD

Assistant Professor of Public HealthDepartment of Family and Community Medicine

13/4/2017

400 B.C.

Let’s talk history..

166218001854

What is Epidemiology?

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How can we define it?

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

What is Epidemiology?

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

scientific, systematic, data-driven

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

frequency, pattern

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

causes, risk factors

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

not just diseases

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

patient is community, individuals viewed collectively

“Epidemiology is the study of the distribution and determinants of health-related states or

events in specified populations, and the application of this study to the control of

health problems.”

public health intervention

Applications

Making individuals decisions

Assessing the community’s

health

Completing the clinical picture

Searching for causes

Descriptive Epidemiology

Who? Where? When?TimePerson PlaceInfluenza

Time

Source: Weekly U.S. Influenza Surveillance Report, CDC.

Place

Source: Weekly U.S. Influenza Surveillance Report, CDC.

Person

Source: Weekly U.S. Influenza Surveillance Report, CDC.

Questions?

Prevention of Diseases

Natural History of Disease Timeline

Stage of Susceptibility

Stage of Subclinical Disease

Stage of Clinical Disease

Stage of Recovery, Disability or Death

ExposurePathologic Changes Onset of Symptoms

Incubation Period

Latency Period

Spectrum of Disease

Natural History of Disease

Subclinical Diseases

Clinical Diseases

Disease Prevention

Primary Prevention

Primordial Prevention

Secondary Prevention

Tertiary Prevention

Levels of PreventionFigure 6.1. Age-standardized death rates from tuberculosis in England andWales, 1840–19681

4000

Dea

th ra

te p

er m

illio

n

3500

3000

2500

2000

1500

1000

500

01840 1860 1880 1900 1920 1940 1960

Year

Tubercle bacillusidentified

Chemotherapy

BCG vaccination

The respective contributions of chronic and infectious conditions to total mor-tality has changed in the last century. For example, in Brazil infectious diseasesaccounted for 45% of all deaths in 1930, but only 5% in 2003 (Figure 6.2). In contrast,the proportion attributed to cardiovascular diseases increased from 12% in 1930 to31% in 2003.

However, mortality rates are influenced over time by the changing age structureof the population, as well as by waxing and waning epidemics. The changes in mor-tality rates in high-income countries have been particularly dramatic in the youngest

Figure 6.2. Changes in contribution of chronic and infectious conditions to total mortality in Brazilian statecapitals, 1930–20033

100%

1930

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

1940 1950 1960 1970 1980 1985 1990 1995 2000 2003

Infectious Cancer External causes Cardiovascular Other illnesses

Proportional mortalityin Brazilian state capitals

- Infectious diseases: 46% in 1930 5% in 2003

- Cardiovascular disease: 12% in 1930 31% in 2003

100 Chapter 6

Age-standardized death rates from tuberculosis in England and Wales, 1840–1968

Before AfterPopulation Individuals

Questions?

Reading

1) Today, 13/April/2017:Introduction: definition of epidemiology, historical overview, concept of health and disease, applications of epidemiology and its relevance to medicine

Descriptive epidemiology: common descriptive variables (person, place, time) -

- CDC Pp. 1-1 to 1-13 - CDC Pp 1-31 to 1-45

2) Next week, 17/April/2017:Epidemiological concepts: spectrum of disease, definition of incubation period, herd immunity, iceberg phenomenon

Levels of disease Prevention: primary prevention; secondary prevention (early detection & screening); tertiary prevention

- CDC Pp 1-59 to 1-61

- Bonita: Chapter 6: P99-115

Reading Material

Thank you..