epidemiology man215 mohamed mb alnoor
DESCRIPTION
EPIDEMIOLOGY MAN215 MOHAMED MB ALNOOR. CONTENTS. Definition of EPIDEMIOLOGY TIME - PLACE - PERSON Morbidity Rates Incidence rate Attack rate Prevalence rate Determinants of disease. Distribution of Disease. Branches, Divisions, Components - PowerPoint PPT PresentationTRANSCRIPT
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.