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PATH216INTRODUTION to GENERAL EPIDEMIOLOGY
Mohamed M. B. Alnoor
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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
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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
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EPIDEMIOLOGY What is Epidemiology?
distribution and
determinants
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EPIDEMIOLOGY What is Epidemiology?
Distribution of Disease
WHEN TimeWHERE Place
WHO Person
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EPIDEMIOLOGY
Distribution of Disease
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EPIDEMIOLOGY
Distribution of Disease
Place• Geographic -Restricted/Wide spread -Coastal/inland• Weather(temp. , humidity , rainfall)• Altitude/latitude/longitude• Urban/rural
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EPIDEMIOLOGY
Distribution of Disease
Person• Age• Sex• Race• Education• Occupation• behavior
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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
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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
:
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EPIDEMIOLOGY
Distribution of Disease
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
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EPIDEMIOLOGY
Distribution of DiseaseInjury Death Rates, Australia, 1992
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EPIDEMIOLOGY
Distribution of Disease
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
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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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
Distribution of disease is quantified as morbidity rates:
Incidence rate Attack rate
Prevalence rate
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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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
rate From October 1, 1990 to Sep 30, 1991?
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
rate From October 1, 1990 to Sep 30, 1991?
4
4/14
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
rate From October 1, 1990 to Sep 30, 1991?
4
4/20
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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.
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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 ?
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
rateFactors affecting incidence:1- New risk factor Contraceptive pills & thromboembolism.
2- Changing virulence H1N1virus & influenza pandemic
3- Changing pattern of interventionChemoprophylaxis & meningitis
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
rateFactors affecting incidence:4-Population patternAging & degenerative diseases & cancer
5- ReportingIncrease in reporting & Early stage of surveillance &
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
rateFactors affecting incidence:6-Screening 7-New diagnostics
New diagnostic
early detection of cases detection of cases
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EPIDEMIOLOGY
Distribution of Diseasemorbidity ratesIncidence
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
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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)
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
= 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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
= 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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
Point prevalence:
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
Point prevalence:
7/18
7
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
From October 1, 1990 to Sep 30, 1991? Period prevalence:
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
From October 1, 1990 to Sep 30, 1991? Period prevalence:
13
4 56
7
9
10
10/20
2
8
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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.
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
prevalence rateFactors affecting prevalence :
1- Incidence rate
Incidence rate
Prevalence rate
averageduration of
disease
& 2- Disease duration
= X
Incidence
Longer duration
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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
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EPIDEMIOLOGY
Distribution of Diseasemorbidity rates
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
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EPIDEMIOLOGY
Distribution of Disease
INCIDENCE VS. PREVALENCE
incidence
Prevalence
Cure Death
Migration