EPIDEMIOLOGY

MAN215

MOHAMED MB ALNOOR

CONTENTS

Definition of EPIDEMIOLOGY

TIME - PLACE - PERSONMorbidity Rates Incidence rate Attack rate Prevalence rate Determinants of disease

Distribution of Disease

Branches, Divisions, ComponentsOf community health (community medicine)

• Health Education• MCH• Environmental health• School health• Occupational health• Control of communicable disease• Control of noncommunicable disease

• Health service administration: - Planning - Implementation - Evaluation• Demography• Community nutrition• Biostatistics• Epidemiology

االشتقاقاتEpidemiology

EPI DEMOS LOGOUPON PEOPLE SCIENCEعلى الناس علم

كاهل ) ( ) جاثم) دراسة

What is Epidemiology?Study of

distribution and

determinantsof

health-related states and eventsIn specified populations

and application of this study to

control health problems.

Distribution of Disease

WHEN TimeWHERE Place

WHO Person

Distribution of Disease

WHEN Time

WHERE Place

WHO Person

Distribution of Disease

WHEN TimeWHERE Place

WHO Person

Distribution of Disease

Time• Changing or stable• Cyclic

• Seasonal• secular

Distribution of Disease

Place• Geographic -Restricted/Wide spread -Coastal/inland• Weather(temp. , humidity , rainfall)• Altitude/latitude/longitude• Urban/rural

Distribution of Disease

Person• Age• Sex• Race• Education• Occupation• behavior

Distribution of disease is quantified as morbidity rates:

?MORBIDITYAny

departure(( subjective or objective))

from state of physiological or psychological

well beingi.e. the extent of illness, injury or disability in a

defined population

Rate: a measure of the occurrence of a health event in a population group at a specified time

period

numeratordenominator

Number of eventsin time period

Number at riskfor the event

:

0

100

200

300

400

500

600

700

10-14yrs

20-24 30-34 40-44 50-54 60-64 70-74 80-84

num

ber

of death

s

Male Female

Age Group

Injury Deaths, Australia, 1992

Injury Death Rates, Australia, 1992

Why are rates useful?

Can help to identify groups with an elevated risk of disease (High-risk Groups).

these groups can be studied to identify “risk factors” .

:High-risk GroupA group of people in the community with a

higher-than-expected likelihood Elevated probability))

for developing a particular disease, or a negative outcome.

RISK The probability that an event will occur.

e.g. that an individual will become ill or die within a stated period of time or age .

Risk factor:

An aspect of personal behavior or lifestyle, an environmental exposure,

or an inborn or inherited characteristic that is associated with

an increased occurrence of disease

or other health-related event or condition.

Why are rates useful? Relate health events to a population base

This provides a basis for making valid comparisons of health events by considering the number at risk in each population

Morbidity rates are used as indicators of health

------------------INDICATORS : Measures used to predict trends , المؤشرات

Distribution of disease is quantified as morbidity rates:

– Incidence rate– Attack rate– Prevalence rate

Incidence rateNumber of new

cases during a year in a locality

Population at risk/ year/locality

=Incidence rate 1OnX

It involves only the new cases. It measures the force of infection or disease in

the community It measures the probability that healthy people

will develop disease during a specified period of time

The numerator has to come from the population at risk for developing disease

The denominator may change over time as people develop disease

The denominator does not include persons with the disease

However, in practicein large studies, the denominator is often the mid-

year populationin small studies, the denominator does not include

persons with the disease

Incidence rate

What is the incidence rate fromOctober 1, 1990 to Sep 30, 1991?

What is the incidence rate fromOctober 1, 1990 to Sep 30, 1991?

4/14

4

What is the incidence rate fromOctober 1, 1990 to Sep 30, 1991?

4/18

4

Example In 1429 the number of breast cancer

cases reported to the cancer registry in Riyadh region was 250. The midyear population of

Riyadh region was four million .

Calculate the incidence rate of breast .cancer in Riyadh

Females constitute 49% of the population.

incidence rate = 250 / 1,960,000 = 0.000128

= 0.128 per 1000 female 1.28 per 10,000 female =

= 12.8 per 100,000 female

Attack rate

Population at risk /period

Attack rate=

Number of episodes during specified period x 10n

Acute recurrent diseases , e.g. URTI, food poisoning. Person may catch the disease more than one time.

Example:In a village of 600 persons, 120 visits to the PHCC were due to food poisoning. What is the attack rate of food poisoning in the village ?

Example:

In a village of 600 persons, 1200 visits to the PHCC were due to flu. What is

the attack rate of flu in the village?

Factors affecting incidence

1 -New risk factor Contraceptive pills & thromboembolism.

Food additives & cancer

New agent HIV & AIDS

2 -Changing virulence

El-Tor vibrio & cholera.

H1N1 Influenza virus & influenza pandemic

Mycobacterial resistance & TB

3 -Changing pattern of intervention

Eradication efforts & poliomyelitis

Chemoprophylaxis & meningitis

Environmental sanitation & filth diseases

4-Population pattern

• Aging & degenerative diseases & cancer

5 -Reporting

• Increase in reporting & • Early stage of surveillance &

incidence

incidence

6-Screening

Screening

early detection of cases

incidence

7-New diagnostics

New diagnostic

detection of cases

incidence

8- Changing classification

Blood pressure 140/80 mmhg Vs 160/90 mmhg

incidence

Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml

incidence

9-Selective migration

Floods or famines

sanitation

susceptibles

incidence

Prevalence rate Point prevalence

Period prevalence

It involves old and new cases .It measures the disease status in the population.It measures the disease burden.

Point prevalence:

Total cases (old + new) at fixed point of time

in a place total population

in that place

x 10n=

prevalence:

Total cases (old + new) during a period of time

in a place total population

in that place

x 10n=

Period

What is the point prevalence on April 1, 1991?

What is the point prevalence on April 1, 1991?

7/18

7

What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991

What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991

123

4

56

7 8

9

10

What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991

123

4

56

7 8

9

10

10/20

example

MOH conducted a survey for RVF among workers in slaughterhouses in Makkah . 224 seropositive workers were identified among 6000 workers.

Calculate the prevalence of RVF.

Factors affecting prevalence

1 -Incidence rate &

Incidence rate

Prevalence rate

averageduration of

disease

2 -Disease duration

= X

Incidence Prevalence

PrevalenceLonger duration

3 -management programs

If successful and curative

If only increases the survival without complete cure

prevalence

prevalence

4 -Changing classification

Blood pressure 140/80 mmhg Vs 160/90 mmhg

Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml

prevalence

prevalenceIncidence

Incidence

5-Selective attrition

If cases of the disease travel to be treated abroad prevalence

prevalence

Incidence Vs. prevalence

incidence

Prevalence

Cure Death

Migration

PNo. I

Time

PNo. I

Time

PNo. I

Time

PNo. I

Time

Determinants of Disease (Analytical Epidemiology)

• Test etiological hypotheses• Identify underlying

• Causes• Risk factors

This HELPS to develop • Sound health programs• Interventions• Policies

Aims of Epidemiology1) To describe the distribution and magnitude of

health and disease problems in human populations.

2) To identify aetiological factors( risk factors) in the pathogenesis of disease.

3) To provide the data essential for planning, implementation and evaluation of services for the prevention, control and treatment of diseases and to the setting up of priorities among these services.