DESCRIPTIVE EPIDEMIOLOGY

PRESENTED BY:

BUSHRA FARHAN

BDS 2010 BATCH

UNDER THE GUIDANCE OF:DR.NEHA AGARWAL

DR.AMITABH VARSHNEYDR. N.D.GUPTA

EPI DEMOS LOGOS

Upon,on,befall People,population,man the Study of

EPIDEMIOLOGY

WHAT IS EPIDEMIOLOGY?

THE STUDY OF THE

DISTRIBUTION DETERMINANTS

OF HEALTH RELATED STATES OR EVENTS IN SPECIFIED POPULATIONS,& THE APPLICATION OF

THIS STUDY TO THE CONTROL OF HEALTH PROBLEMS.

-JOHN M.LAST(1988)

EPIDEMIOLOGICAL

METHODS

DESCRIPTIVE EPIDEMIOLOGY

ANALYTICAL EPIDEMIOLOGY

EXPERIMENTAL EPIDEMIOLOGY

DESCRIPTIVE

EPIDEMIOLOGY

CONCERNED WITH OBSERVATION OF THE DISTRIBUTION OF THE DISEASE OR ANY HEALTH RELATED EVENTS IN HUMAN POPULATIONS & THE IDENTIFICATION OF THE CHARACTERISTICS WITH WHICH THE DISEASE OR CONDITION UNDER STUDY SEEMS TO BE ASSOCIATED.

o DESCRIBES THE PATTERN OF OCCURRENCE OF DISEASE OR A CONDITION RELATIVE TO OTHER CHARACTERISTICS OF THE POPULATION.

o FIRST PHASE OF ANY EPIDEMIOLOGICAL INVESTIGATION.

STEPS :

DEFINING THE POPULATION TO BE STUDIED.

DEFINING THE DISEASE UNDER STUDY.

DESCRIBING THE DISEASE IN TERMS OF PERSON,PLACE & TIME.

MEASUREMENT OF THE DISEASE.

COMPARING WITH KNOWN INDICES.

FORMULATING AN ETIOLOGICAL HYPOTHESIS

1.DEFINING THE POPULATION TO BE STUDIED:

DEFINED

POPULATION

POPULATION TO BE STUDIED IS DEFINED IN TERMS OF:

TOTAL NUMBER COMPOSITION OF THE INDIVIDUALS

THE POPULATION SELECTED FOR THE STUDY SHOULD ALWAYS REMAIN STABLE,WITHOUT ANY MIGRATION INTO OR OUT OF THE AREA.

PARTICIPATION OF THE PEOPLE OF THE COMMUNITY CHOSEN.

PRESENCE OF HEALTH FACILITY IN CLOSE PROXIMITY TO THE COMMUNITY.

IMPORTANCE: IT FORMS THE POPULATION AT RISK,WHICH PROVIDES THE DENOMINATOR FOR CALCULATING THE RATES OF FREQUENCY AND DISTRIBUTION OF THE DISEASE.

2.DEFINING THE DISEASE UNDER STUDY

THE DISEASE NEEDS TO BE DEFINED WITH AN

IT CLEARLY INDICATES THE CRITERIA BY WHICH THE DISEASE CAN BE MEASURED.

OPERATIONAL DEFINITION

WITH WHICH THE DISEASE OR CONDITION CAN BE IDENTIFIED & MEASURED IN THE DEFINED POPULATION WITH A DEGREE OF ACCURACY.

3.DESCRIBING THE DISEASE UNDER STUDY:

WHO?

WHERE?

WHEN?

PERSON

PLACE

TIME

TIME DISTRIBUTION

SHORT TERM FLUCTUATIONS:

EPIDEMIC

THE OCCURENCE OF CASES OF AN ILLNESS OR OTHER HEALTH RELATED EVENTS IN A REGION OR A COMMUNITY CLEARLY IN EXCESS OF NORMAL

EXPECTANCY.

TYPES OF EPIDEMICS:

1.COMMON SOURCE

•SINGLE EXPOSURE OR POINT SOURCE

•CONTINUOUS OR MULTIPLE EXOSURE

2.PROPAGATED•PERSON TO PERSON

•ARTHROPOD VECTOR

•ANIMAL RESERVOIR

3.SLOW OR MODERN

COMMON SOURCE EPIDEMICS:

SINGLE EXPOSURE

•RESPONSE OF A GROUP OF PEOPLE TO A SOURCE OF INFECTION OR CONTAMINATION TO WHICH THEY WERE EXPOSED ALMOST SIMULTANEOUSLY.

•CASES DEVELOP WITHIN 1 INCUBATION PERIOD.

•Eg:FOOD POISONING

CONTINUOUS EXPOSURE

•EXPOSURE FROM THE SAME SOURCE MIGHT BE PROLONGED.

•NEED NOT BE AT THE SAME PLACE OR AT THE SAME TIME.

•Eg:CONTAMINATED WATER

PROPAGATED EPIDEMIC:

a.PERSON TO

PERSON

b.ARTHROPOD

VECTOR

c.ANIMAL

RESERVOIR

MOST OFTEN OF INFECTIOUS ORIGIN.

USUALLY OCCURS IN PLACES WHERE LARGE NUMBER OF SUSCEPTIBLE INDIVIDUALS ARE AGGREGATED OR WHERE THERE IS A REGULAR SUPPLY OF NEW SUSCEPTIBLE PERSONS,WHICH TENDS TO LOWERTHE HERD IMMUNITY.

2.PERIODIC FLUCTUATIONS

SEASONAL TRENDS CYCLIC TRENDS

3.LONG TERM OR SECULAR TRENDS

o CHANGES IN DISEASE FREQUENCY THAT OCCUR GRADUALLY OVER A LONG PERIOD OF TIME.

o ORAL CANCER HAS SHOWN AN UPWARD TREND IN PAST 50 yrs WHILE TB,TYPHOID & POLIO HAVE SHOWN A DOWNWARD TREND.

PLACE DISTRIBUTIONS:

THE GEOGRAPHIC PATTERN OF DISEASE PROVIDE CLUES ABOUT THE

ETIOLOGY OF DISEASE.

INTERNATIONAL VARIATIONS

NATIONAL VARIATIONS

RURAL-URBAN VARIATIONS

LOCAL DISTRIBUTIONS

MIGRANT STUDIES:

EVALUATE THE ROLE OF POSSIBLE GENETIC AND ENVIRONMENTAL

FACTORS IN THE OCCURRENCE OF DISEASE IN A POPULATION.

USUALLY OF TWO TYPES:

COMPARING THE RATE OF OCCURRENCE OF DISEASE FOR MIGRANTS WITH THOSE OF THEIR KIN WHO HAVE STAYED AT HOME.

COMPARISON OF GENETICALLY SIMILAR GROUPS LIVING UNDER DIFFERENT ENVIRONMENTAL CONDITIONS.

IF RATE OF DISEASE OCCURRENCE IN MIGRANTS SIMILAR TO THAT OF COUNTRYOF ADOPTION OVER A PERIOD OF TIME:

ENVIRONMENTAL FACTOR

COMPARING THE RATE OF OCCURRENCE OF DISEASE IN MIGRANTS WITH THE LOCAL POPULATION OF THE HOST COUNTRY.

COMPARISON OF GENETICALLY DIFFERENT GROUPS LIVING IN A SIMILAR ENVIRONMENT.

IF RATE OF DISEASE OCCURRENCE AMONG THE MIGRANTS ARE SIMILAR TO THEIR COUNTRY OF ORIGIN:

GENETIC FACTORS

PERSON DISTRIBUTION:

AGE

BIMODALITY

GENDER

ETHNIC GROUP

OCCUPATION

SOCIOECONOMIC STATUS

MARITAL STATUS

BEHAVIOUR

•AGE:

IT MAY ASSIST IN UNDERSTANDING THE FACTORS RESPONSIBLE FOR THE

DEVELOPMENT OF DISEASE.

AGE MAY PRODUCE INDIRECT EFFECT THAT MUST BE TAKEN ACCOUNT OF.

ALSO USEFUL FOR ADMINISTRATIVE PURPOSES.

•BIMODALITY:

OCCURRENCE OF TWO SEPARATE PEAKS IN THE AGE INCIDENCE OF A DISEASE.

INDICATES THAT MATERIAL IS NOT HOMOGENOUS,THAT ENTITY UNDER EXAMINATION MAY BE DIVIDED INTO TWO.

GENDER:VARIATION IN DISEASE FREQUENCY IN MALES & FEMALES.

SOCIOECONOMIC STATUS:UPPER SOCIAL CLASS INDIVIDUAL EXHIBIT BETTER HEALTH STATE.

MARITAL STATUS:HELPS IN INVESTIGATING POSSIBLE INFLUENCE OF A COMMON ENVIRONMENT ON THE HEALTH OF

MARITAL PARTNERS.

• OCCUPATION:

AS A MEASURE OF SOCIOECONOMIC STATUS.

FOR IDENTIFICATION OF RISKS ASSOCIATED WITH EXPOSURE TO AGENTS PECULIAR TO CERTAIN OCCUPATIONS.

TO IDENTIFY GROUPS WHOSE GENERAL PATTERNS OF LIFE VARY BECAUSE OF DIFFERENT DEMANDS MADE BY THEIR OCCUPATION.

• BEHAVIOUR:

HABITS LIKE SMOKING,ALCOHOLISM,DRUG ABUSE,SEDENTARY LIFESTYLE OR OVEREATING CAN LEAD TO

CERTAIN INFECTIOUS DISEASES LIKE TYPHOID,CHOLERA SPREAD THROUGH MOVEMENT OF PEOPLE IN MASSES SUCH AS IN PILGRIMAGE.

CORONARY ARTERY DISEASE, HYPERTENSION,CANCERS,OBESITY ETC

4.MEASUREMENT OF DISEASE:

DONE IN TWO TERMS:

MORBIDITY

MORTALITY

INCIDENCE PREVALENCE

EXPRESSED IN TERMS OF

LONGITUDINAL

STUDY

CROSS SECTIONAL

STUDY

CROSS SECTIONAL STUDIES

A SET OF INDIVIDUALS ARE CHOSEN WHO MAY BE A REPRESENTATIVE SAMPLE OF THE CHOSEN POPULATION.

THE MEASUREMENTS OF EXPOSURE AND EFFECT ARE MADE AT THE SAME TIME.

THIS PROVIDES INFORMATION ON THE RELATIONSHIP BETWEEN A DISEASE AND OTHER VARIABLES OF INTEREST.

EASY & ECONOMICAL TO CARRY OUT.

“CROSS SECTIONAL STUDIES DONE FOR LONGER DURATION BY REPEATING PERIODICALLY.”

SAME INDIVIDUALS ARE EXAMINED UPON REPEATED OCCASIONS & THE CHANGES WITHIN GROUP ARE RECORDED IN TERMS OF ELAPSED TIME

BETWEEN OBSERVATIONS.

BUT MORE TIME CONSUMING.

LONGITUDINAL STUDIES

USEFUL FOR:

STUDYING THE NATURAL HISTORY

OF THE DISEASE & ITS OUTCOME.

IDENTIFYING THE RISK FACTORS ASSOCIATED

WITH THE DISEASE.

CALCULATING THE INCIDENCE

RATE OF THE DISEASE.

5.COMPARING WITH KNOWN INDICES

BY MAKING COMPARISON BETWEEN DIFFERENT POPULATIONS & SUBGROUPS OF THE SAME POPULATION

POSSIBLE TO REACH A CONCLUSION WITH REGARD TO THE DISEASE ETIOLOGY & TO IDENTIFY SUBGROUPS AT RISK.

6.FORMULATION OF AN ETIOLOGICAL HYPOTHESIS

HYPOTHESIS:

“A SUPPOSITION ARRIVED AT FROM BY OBSERVATION OR BY REFLECTION”.

SPECIFICATIONS OF HYPOTHESIS:

POPULATIONTHE CAUSE BEING

CONSIDEREDTHE EXPECTED

EFFECT

DOSE-RESPONSE RELATIONSHIP

TIME-RESPONSE RELATIONSHIP

USES:

PROVIDES DATA WITH REGARD TO THE TYPES OF DISEASE PROBLEMS & THEIR MAGNITUDE IN THE COMMUNITY.

PROVIDES INFORMATION ON THE ETIOLOGY OF A DISEASE & HELPS IN THE FORMULATION OF AN ETIOLOGICAL HYPOTHESIS.

PROVIDES DATA REQUIRED FOR THE PLANNING,ORGANIZING & EVALUATING PREVENTIVE & CURATIVE SERVICES.

LEADS THE PATH FOR FURTHER RESEARCH WITH REGARD TO A PARTICULAR DISEASE PROBLEM.

THANK YOU!!