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Epidemiological Methods

Study of distribution and determinants of health related events and its application to control health problems.

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Enumerate two different types of epidemiological methods .

To define descriptive epidemiology and describe importance of time, place and person distribution.

Enumerate three kinds of time fluctuations in disease occurrence.

To describe disease load in terms of prevalence and incidence.

To differentiate cross sectional and longitudinal studies.

To enumerate two used of descriptive epidemiology.

At the end of the session, you will be able to

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Epidemiology: Definition

Dynamic study of theDeterminantsOccurrenceDistributionControl Pattern

Of health and disease in a population

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So, Epidemiology Is the basic science of public health

Provides insight regarding the nature, causes, and extent of health and disease

Provides information needed to plan and target resources appropriately

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Epidemiology is a Quantitative Discipline Measures of frequency

◦ Counts and rates Measures of association

◦ Relative risk◦ Odds ratio

Statistical inference◦ P-value◦ Confidence limits

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Observational studies- Investigator only measures. Does not interfere. --Descriptive studies. --Analytical studies .

Experimental studies. Also called Interventional studies. – Active attempt by investigator.

To Study disease occurrence

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Kinds of EpidemiologyDescriptive

Analytic

Experimental

Further studies to determine the validity of a hypothesis concerning the occurrence of disease.

Deliberate manipulation of the cause is predictably followed by an alteration in the effect not due to chance

Study of the occurrence and distribution of disease

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Descriptive vs.Analytic Epidemiology

Descriptive

Used when little is known about the disease

Rely on preexisting data

Who, where, when

Illustrates potential associations

Analytic Used when insight

about various aspects of disease is available

Rely on development of new data

Why

Evaluates the causality of associationsBoth are important!

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Observation on population or individual. (dengue in gokula ).

Time distribution- When disease occurring?

Place distribution- Where ? Person –Who is getting it ?

Observational studies-descriptive

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1. Defining population-Whole population in a geographic area, or representative population. Should be large enough. Age, sex, occupation and other information. Also called Population at Risk. Framingham study !

Descriptive Epidemiology

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2. Disease under study-Precise with validity. Well defined diagnostic method acceptable to the population. If not defined precisely, it leads to errors. Operational definition of the disease. Once accepted, it cannot be changed. Example- Dengue.

Descriptive Epidemiology-

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Disease is seasonal, ? Periodic fluctuation ? Short term fluctuation –

EPIDEMIC .-’’Occurrence in a community of illness or event clearly in excess of normal expectancy.”

Periodic fluctuation Long term trends-

Descriptive -Time distribution

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Endemic, Epidemic and Pandemic Endemic - The habitual presence (or usual occurrence)

of a disease within a given geographic area Epidemic - The occurrence of an infectious disease

clearly in excess of normal expectancy, and generated from a common or propagated source

Pandemic - A worldwide epidemic affecting an exceptionally high proportion of the global population

Number of Casesof Disease

Time

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Common source epidemic- 1.Point source- brief exposure, epidemic is severe, all case in one incubation period. –Food poisoning. 2. Continuous or repeated exposure- Gonorrhea, respiratory infection, water contamination.

Types of epidemics

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Infectious, Person to person. Gradual rise, fall over a long period. Long term transmission. Herd immunity ?

Types of epidemics- Propagated epidemics

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Seasonal trend, -Measles, URTI, Diarrhea,. Cyclic trend- Influenza (H1N1).

Long term trends- CVD, Tuberculosis, NIDDM.

Periodic fluctuations

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Geographical variation- environment, diet, etc.

International variation- Ca stomach (Japan Vs USA ) , Ca Oral cavity (India )

National variation – Malaria –Sabah , Sarawak. Filariasis- Perak, Sabah.

Migration studies- Tuberculosis among migrants in Malaysia.

Place distribution.

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PersonAge HobbiesSex PetsOccupation TravelImmunization status Personal HabitsUnderlying disease StressMedication Family unitNutritional status SchoolSocioeconomic factors GeneticsCrowding Religion

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Disease load in a population. Mortality, Morbidity, Disability . Morbidity- Incidence, Prevalence. Prevalence- All current cases existing at a

given point of time in a given population. Incidence- Number of NEW cases occurring

in a defined population during a specific time.

How to measure ? Hypothesis.

Measurement of disease

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Measures Morbidity: Refers to the presence of disease

in a population

Mortality: Refers to the occurrence of death in a population

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Prevalence vs. Incidence

Prevalence is the number of existing cases of disease in the population during a defined period.

Incidence is the number of new cases of disease that develop in the population during a defined period.

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PrevalencePrevalence: The number of existing cases in

the population during a given time period.

PR = # existing cases during time period

population at same point in time

Prevalence rates are often expressed as a percentage.

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Incidence Rates Population denominator:

IR = # new cases during time period X Kspecified population at risk

Example (Incidence Rate)During a six-month time period, a total of 53

nosocomial infections were recorded by an infection control nurse at a community hospital. During this time, there were 832 patients with a total of 1,290 patient days. What is the rate of nosocomial infections per 100 patient days?

IR = 53 X 100

1,290 pt. days = 4.1 infections per

100 pt. days

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What is a hypothesis? An educated guess

an unproven idea

based on observation or reasoning, that can be proven or disproven through investigation.

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Cross sectional-Single examination of a cross section of population. Prevalence study.

Longitudinal Repeated observation in the same population.

Studies

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Uses of Descriptive Epidemiology

trends in health and disease and allow comparisons among countries and subgroups within countries

Provides clue to disease etiology. provides a basis for planning, provision

and evaluation of services identifies problems to be studied by

analytic methods (?)and to test hypotheses related to those problems

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. Circle the most appropriate explanation on “Prevalence rate”:

a. the number of patients who have the disease at a particular time, divided by the population at risk of having the disease at that time.

b. the number of new cases of a diseased in a population over a period of time.

c. not useful for developing HIV/AIDS control programme. d. useful for developing Avian flu control programme. e. not useful for any disease control programme.

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What is Epidemic ?

What is endemic ?

What is pandemic ?

Questions

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1. Define population 2. Define the disease 3. Randomized trial 4. Measurement of a disease. 5. Formulate an hypothesis.

Following are steps in Descriptive studies

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