epidemiology for master degree, Study notes of Epidemiology

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Aug 2021 Lecture

By Tilaye W[MPH/Epid, Asst. Prof.] Introduction to Epidemiology

Course outline

Definitions, Concepts and History of Epidemiology

Natural history of disease

Level of disease prevention

Concepts and types of disease causation models

Discussion

How do you define epidemiology?

What are the purposes of epidemiology?

What is natural history of diseases?

What is the cause of a disease?

Definition of Epidemiology Greek Term: EPI - Upon DEMOS - People LOGOS - Study of, Body of knowledge

Key words in the definition are: 1.Frequency=> # of cases in a popn^ /quantification of cases/ 2.Distribution=> who? Where? And when? of health and health related events occurrence ( Person, Place, Time ) 3.Determinants=> event, characteristic or any definable entity that brings about change in health and health related conditions

It refers to “why diseases occur in certain places? In a certain period? Or in a certain popn^ groups?”  (^) Env’tal, socio-economic, genetic, life style, ……

determinants of health

Key words …

3. Health and health related events

 (^) Epidemiology is concerned not only with disease but events like birth, death, migration, accidents, e.t.c

4. Human population

 Epidemiology is concerned with human popn, there is strong interrelation with clinical medicine

5. Application

 Epidemiology is an applied science.

 The purpose of all epidemiological studies is the

prevention and control of health problems

Two fundamental assumptions of Epidemiology 1.Non-random distribution of diseases: disease occurrence in a popn^ is not random or by chance  (^) There are patterns of occurrence in which some behavioral, environmental and other factors increase the risk of acquiring/developing a particular disease

2. Human disease has causal and protective factors that can be identified through systematic investigation of d/nt popn

Scope of Epidemiology Since 5th century Middle of 20 th^ century Past 25 yrs Recently

Epidemic of

communicable diseases

Endemic

communicable

diseases &

Non communicable

diseases

Chronic diseases,

injuries,

birth defects, MCH,

Occupational health,

Env’tal health

Health related behavior

Genetic markers of disease risks

▲ + ▲ + ▲ + ▲+

History of epidemiology… John Snow (1813-1858) -In 1854,  controlled cholera epidemic  44 years before vibrio was identified

Developments in modern epidemiology

Observational analytic Studies

Case-control studies

Doll & Hill

Smoking and carcinoma of the lung: Preliminary report

in 1950 investigated the r/sh b/n cigarette smoking and

lung cancer.

Cohort Studies

 The Framingham Heart Study: to identify cause of

cardiovascular disease(CVD)

• 5,000 residents included in the study and follow-up is now about 65

yrs

Natural History of Disease  It refers to the progression of disease process, in the absence of intervention  It begins with exposure to causative agent capable of producing disease  Without intervention, the process ends with recovery, disability or death  Halted at any time in the progression by intervention, host factors, other influences

NATURAL Hx … Two gradients/dynamics in Natural Hx of disease 1.Dynamics of infection: stages in this dynamics are susceptible, latent period, infectious period and non infectious (dead, recovered). => Time line for infection is important for the parasite/agent and public health

2. Dynamics of disease: stages in this dynamics are susceptible, incubation period, symptomatic period, non diseased (dead, removed, immune, carrier). => Time line for disease is important to infected person and health worker

Stages in natural history of disease 1.Stage of susceptibility: a stage in which d/se has not developed but the ground work has been laid by presence of factors that favor its occurrence  (^) Susceptible person is lacking sufficient resistance to particular pathogenic agent to prevent disease

2. Incubation period- is the time interval b/n entry and dev’t of signs and symptoms of d/se  (^) It is the time interval b/n the entry of pathogenic micro-organism and sufficient multiplication to cause pathology that will produce signs and symptoms of disease

• (^) Incubation period in infectious diseases, is equivalent to combination of induction and latent periods in non infectious diseases
• (^) Induction period is the period of time from causal action until disease initiation
• Latent period: The period b/n exposure and onset of infectiousness (this may be shorter or longer than the incubation period)