g path216 introdution to general epidemiology mohamed m. b. alnoor

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PATH216INTRODUTION to GENERAL EPIDEMIOLOGY

Mohamed M. B. Alnoor

EPIDEMIOLOGY

CONTENTS

Definition of EPIDEMIOLOGY Other Definitions

TIME - PLACE - PERSON Morbidity Rates Incidence rate Attack rate Prevalence rate Determinants of disease

Distribution of Disease

Branches of community medicine

EPIDEMIOLOGY What is Epidemiology?Epidemiology is

theStudy of

distribution and

determinantsof

health- related states and eventsIn specified populations

and application of this study to control health problems.

distribution and

determinants

EPIDEMIOLOGY What is Epidemiology?

distribution and

determinants

EPIDEMIOLOGY What is Epidemiology?


WHEN TimeWHERE Place

WHO Person

EPIDEMIOLOGY


EPIDEMIOLOGY


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

EPIDEMIOLOGY


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

EPIDEMIOLOGY

Distribution of DiseaseDistribution of disease is quantified as

morbidity rates:

i.e. the extent of illness, injury or disability in a defined population

MORBIDITY :Any

departure ((subjective or objective ))

(physiological or psychological) from state of

well being

EPIDEMIOLOGY

Distribution of DiseaseDistribution of disease is quantified as

morbidity rates:occurrence

time periodpopulation group

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

:

EPIDEMIOLOGY


0100200300400500600700

10-14yrs

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

num

ber o

f dea

ths

Male Female

Age Group

Injury Deaths, Australia, 1992

EPIDEMIOLOGY

Distribution of DiseaseInjury Death Rates, Australia, 1992

EPIDEMIOLOGY


0100200300400500600700

10-14yrs

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

num

ber o

f dea

ths

Male Female

Age Group

Injury Death Rates, Australia, 1992

Injury Deaths, Australia, 1992

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesWhy are rates

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

these groups can be studied to identify “risk factors”

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

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

Distribution of disease is quantified as morbidity rates:

Incidence rate Attack rate

Prevalence rate

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesIncidence

rate Number of new cases during a year

in a locality

Population at risk/ year/locality

=Incidence rate 1On

It involves only the new cases. It measures the probability that healthy people will develop disease during a specified period

of time

X

EPIDEMIOLOGY


The numerator is new cases The denominator may change over time as people

develop disease However, in practice in large studies, the denominator is often the mid-

year population in small studies, the denominator includes persons at risk of the disease

Incidence rate

EPIDEMIOLOGY


rate From October 1, 1990 to Sep 30, 1991?

EPIDEMIOLOGY



4

4/14

EPIDEMIOLOGY



4

4/20

EPIDEMIOLOGY


rateExample In 2009 the number of breast cancer cases reported to the cancer registry in Riyadh region was 250 cases. The midyear population of Riyadh region was four million.

Calculate the incidence rate of breast .cancer in Riyadh

EPIDEMIOLOGY


rateFemales 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

EPIDEMIOLOGY


Attack rate

Population at risk/ period

Attack rate =

Number of episodes during specified period

x 10n

Acute recurrent diseases , e.g. URTI, food poisoning. A person may catch the disease

more than once.

EPIDEMIOLOGY


Attack rate

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 ?

EPIDEMIOLOGY


Attack rate

Example:

In a village of 600 persons, 120 visits to the PHCC were due to flu.

What is the attack rate of flu in the village ?

0

EPIDEMIOLOGY


rateFactors affecting incidence:1- New risk factor Contraceptive pills & thromboembolism.

2- Changing virulence H1N1virus & influenza pandemic

3- Changing pattern of interventionChemoprophylaxis & meningitis

EPIDEMIOLOGY


rateFactors affecting incidence:4-Population patternAging & degenerative diseases & cancer

5- ReportingIncrease in reporting & Early stage of surveillance &

EPIDEMIOLOGY


rateFactors affecting incidence:6-Screening 7-New diagnostics

New diagnostic

early detection of cases detection of cases

EPIDEMIOLOGY


rateFactors affecting 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

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesPrevalence

rate Point prevalence

Period prevalence

It involves old and new cases It measures the disease status in the

population.It measures the disease burden.

( All Cases)

EPIDEMIOLOGY


= 1OnX

Prevalence rate

Point prevalence:

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

in a place total population in that place

EPIDEMIOLOGY


= 1OnX

Prevalence rate

Period prevalence:

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

in a place total population in that place

EPIDEMIOLOGY


Point prevalence:

EPIDEMIOLOGY


Point prevalence:

7/18

7

EPIDEMIOLOGY


From October 1, 1990 to Sep 30, 1991? Period prevalence:

EPIDEMIOLOGY


From October 1, 1990 to Sep 30, 1991? Period prevalence:

13

4 56

7

9

10

10/20

2

8

EPIDEMIOLOGY


prevalence rate

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

Calculate the prevalence of RVF.

EPIDEMIOLOGY


prevalence rateFactors affecting prevalence :

1- Incidence rate

Incidence rate

Prevalence rate

averageduration of

disease

& 2- Disease duration

= X

Incidence

Longer duration

EPIDEMIOLOGY


prevalence rateFactors affecting prevalence :3- management programsIf successful and curative If only increases the survival without complete cure

4- Selective attrition If cases of the disease travel to be treated abroad

EPIDEMIOLOGY


prevalence rateFactors affecting prevalence :

5- Changing classificationBlood pressure 140/80 mmhg Vs 160/90 mmhg

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

Incidence

Incidence

EPIDEMIOLOGY


INCIDENCE VS. PREVALENCE

incidence

Prevalence

Cure Death

Migration

g path216 introdution to general epidemiology mohamed m. b. alnoor

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