DESCRIPTIVE EPIDEMIOLOGY

PRESENTED BY:

BUSHRA FARHAN

BDS 2010 BATCH

UNDER THE GUIDANCE OF:

DR.NEHA AGARWAL DR.AMITABH VARSHNEY

DR. 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 EPIDEMIOLOG

Y

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:

TOTAL POPULATIO

N IN A GEOGRAPHI

C AREA

REPRESENTATIVE

SAMPLE TAKEN

FROM THAT POPULATIO

N

DEFINED POPULATION

POPULATION TO BE STUDIED IS

DEFINED IN TERMS OF:

TOTAL NUMBERCOMPOSITION

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?

PERSONPLACE

TIME

TIME DISTRIBUTION

SHORT TERM FLUCTUATIONS

PERIODIC FLUCTUATIONS

LONG TERM FLUCTUATIONS OR SECULAR TRENDS

SHORT TERM FLUCTUATIONS:

EPIDEMICTHE 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

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:

IDENTIFYING THE RISK FACTORS ASSOCIATED WITH

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

CONSIDERED

THE EXPECTED EFFECTDOSE-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!!