Transcript Incidence Rate

Dr. Bassam Hijawi
Epidemiologist
Director of Jordan Cancer Registry
Director of Health Promotion
1
In Epidemiology
The most important tool for
measuring the risk of occurrence of
a particular event in a population
during a given time period are :-
2
Rates
Morbiditly Rats:
Measuring the occurrence (probability ,
risk) of disease (includes illness, injury, or
disability). A term preferably avoided, used
incidence rate or prevalence rate
Mortality Rates:
Measuring the occurrence of deaths. A term
preferably a voided, many crude and specific
death rates used. (indices of health ).
3
Rates , may be :
Crude Rates.
Specific Rates.
Standardized (adjusted ) Rates.
Example :
Population :
6,000 Men
4,000 Women
10,000 Total
Proportion : tell us what fraction of the population is affected .
6000
-Proportion of men =
6000 + 4000
= 0.60 = 60%
- Ratio M/F
=
6000
4000
Ratio F/M
=
4000
6000
=3:2
=2:3
4
Example :
-
( 40) new cancer lung cases reported during the yare 2004 from the previous
population (30 among men and 10 among Women ). 6 cases died during the
same year .
(5 among men and 1 among women )
Rates : tell us how fast the disease is occurring in a population .
-
Lung Cancer Incidence Rate
=
40
10,000
-
=4
/1000
X 10,000
= 25 /10,000
Female Lung cancer Incidence Rate =
10
4000
-
X 1000
Lung cancer death Rate =
6
10,000
X 10,000 = 6
/10,000
X 100,000 = 60 /100,000
X 1000
= 0.6 /1000
5
Measures of Disease Occurrence
Morbidity Rates
Routinely collected data on illness from different sources :
1.
Incidence Rate:
The number of new cases of a disease that occur during a specified
period of time in a population at risk for developing a disease .
IR per 1000
No. of new cases of a disease occurring in the
population during a specified of time
=
_________________________________________________________________
x
1000
No. of persons at risk of developing the disease
during that period of time
6
The disease developed in a person who did not have the disease
previously.
Transition from a non disease to diseased state.
Measure of risk in exposed population .
Denominator = number of people who are at risk for developing the
disease (estimated mid year population )
Any individual in the denominator, may (must have) to become
counted in the numerator. (numerator included in the denominator).
Incidence for uterine cancer, the denominator must be women. Mean,
men not at risk to develop uterine cancer.
Period of time must known, must specified for all individuals in the
denominator. Incidence may be calculated in one week, one month,
one year, 5 years.
7
Pupulation at risk in a study of cervix carcinoma
0-25 Y.
All
MEN
All
WOMEN
25- 69
Y.
25- 69
Y.
70 + Y.
Total Population
1.
2.
3.
All Women (Age
groups
Population
At risk
Defining pop. At risk:
Improve accuracy ( rate not diluted .
People who cannot contract the dis. are not included in the denominator.
Ex.
–
Occupational injuries occur among working people .
–
Brucellosis occur among people handling infected animals .
8
(farms + slaughter houses
Cumulative Incidence :
Example : 482 women using oral contraceptive, followed for 3 years .
27 of them developed Bacterurea.
C.I of Bacterurea among O.C users =
27
482
X 3 years = 5.6 person- years during three years.
( Assume all persons have been followed during the 3 years period )
Incidence Density :
–
Due to loss of follow up (attrition ) for any reason, different individual in the
denominator, may be observed for different length of time, person- years used in
the denominator.
–
(Unequal Periods of observation )
–
Valid under these conditions:
1.
Risk of disease or death is constant . Throught the study period.
2.
Rate of disease or death the same between those lost to follow up and those not.
3.
Disease under study must be not rapidly fatal.
9
Example: 1000 persons followed , (some leave, some
dropout some die, some migrate… )end by 800
Example :
Jan. July
90
Jan. July
91
Jan. July
92
Jan. July
93
Jan. July
94
Years followed
2
3
5
4
2.5
1.
2.
3.
4.
5.
Total years at risk 16.5
ID = 2 cases / 16.5 person years
= 12.1 / 100 person – years observation
( Incidence Density )
10
Attack Rats
It is incidence rate.
Usually expressed as percentage
Used for particular population .
Observed for limited period of time.
Used mostly in outbreaks/ epidemics.
11
Secondary attack rate
Used in propagated spread .
Number of new cases in group minus
initial case (s).
= ______________________________________ x 100
Number of susceptible persons in
group minus initial case (s)
During a specified time period .
Index case (s) excluded from both numerator and
denominator .
12
Specification of Numerator
(Number of persons + Number of conditions)
More than one event can occur to the same person
within stated time period .
This incidence rate tells us the number of events (colds)
to be expected among the group of people in that year .
Incidence rate = Number of colds
PAR
In one year period .
= Number of people who developed a cold
PAR
In one year period.
This incidence rate tells us about the probability that any
person will develop a cold in one year.
13
Mortality Rates
•
Annual M.R. for all causes /1000 POP.
C.D.R
•
=
Total No. of deaths from all
causes in (Y.)
No. of persons in the mid Y.
POP.
x 1000
Annual M.R from all causes for children younger than 10 Y. /
1000 POP.
restriction on age
applied to Num. + Denominator
specific Rate
Age specific M.R
Restriction on dis./ specific // Cause
Cause Specific Death Rate
(No. of deaths from lung cancer in one year ).
Restriction for ( specific age and specific Cause )
Ex. Annual M.R for leuk. For children < 10 Y.
Leading cause of death
14
•
Case Fatality Rate
CFR
No. of deaths during a
specified period of time after
dis. onset or diag.
=
x 100
No. of individuals with the
specified dis.
Difference CDR + CFR
* Measure of the severity of the dis.
* Measure any benefits of a new therapy
•
Therapy improve =
CFR
Proportionate Mort. Rate.
PMR
=
No. of deaths from dis. X
place / time
x K
Total Deaths
Means: What proportion of deaths attributed to Dis. X. ?
15
Comparison of
M.R,
PMR,
All causes
H.D
Community A
Community B
M.R
(all causes )
30/1000
15/1000
P.M.R
( Heart dis.)
10 %
20%
M.R
(Heart dis.)
3/1000
3/1000
P.M.R = give us a quick look at the major causes of
deaths, but can not tell us the risk of dying
from a dis.
We Need
M R for that .
16
Years of Potential Life Lost
YPLL
In younger age
Injuries, accidents, cancer…
Cause specific M.R
10th
YPLL
6th
HIV
Younger
Involves a greater loss of future
productive years than were it to
occur at an older age.
17
When M R is a good index of
incidence ? Measure of dis. risk
Under 2 conditions :
rabies
– CFR is
– Duration of dis is short ( Survival )
Cancer pancreas
Problems with Mortality Data
Death Certificate Problems
[ underlying cause of death ]
[ Immediate cause of death ]
ICD
18
Morbidity Indices
Prevalence
No. of current cases ( new + old) of a dis.
existing at a given point in time in an area.
Point Prevalence =
Estimated POP. At risk at the same point in
Rate
time in the same area.
Period Prevalence =
Rate
No. of cases ( new + old) of a dis. existing
during a time interval .
Estimated mid – interval POP. At risk
x K
x K
19
Special type of incidence, Prevalence
Rate
Type
Numerator
Denominator
Morbidity R.
I
New cases of Non- fatal
Dis.
Total POP. at Risk
Mortality R.
I
No. of Death from a dis.
(or all causes)
Total POP.
Case- Fatality R.
I
No. of Deaths from a dis.
No. of cases of that dis
Disease Rate at
Autopsy
P
No. of cases of a dis.
No. of persons
autopsied
Birth Defect
Rate
P
No. of babies with a given No. of Live Births
abnormalities
Period
Prevalence Rate
P
No. of new cases and
existing cases during a
given time period
Total POP.
Attack Rate
I
No. of cases of dis.
Total POP. at
Risk for a limited
period of observation 20
Ex. Breast Cancer I.R. in Women by age
Annual Rate
/
100,000
400
300
percent
of total
cases
200
100
0
35
25
30
35
40
45
50
55
60
65
70
75
80
85
Age
Distinction between
– Distribution of dis.
– Proportion of cases
– I.R (risk of the dis.).
21
Prevalence Rate ( P)
P
=
No. of cases of a dis. Present in the POP. at a
specified time
No. of persons in the Pop. at that specified
time
x K
How many people have arthritis ?
Household Survey ?
Interviews , physical ex.
(I) + (P) difference
We don’t take into account the duration of the dis.
‫متى حدث‬
Numerator mix . : not Measuring risk.
Point Prevalence : (p) at a point in time
Period Prevalence .
22
Ex. Questions regarding asthma
Do you currently have asthma. ?
Point Prevalence .
Have you had asthma during the last (n) years?
Period Prevalence .
Have you ever had asthma. ?
‫عمرك اصبت باألزمة‬
Cumulative Incidence
23
Mortality :
Routinely collected data on deaths from different sources.
1.
Crude Death Rate:
No. of deaths among residents in an area/year
=
2.
Total POP.
x
K
Specific Rates :
A . Cause specific death rate:
No. of deaths ( place – time ) from specific dis
=
Total POP.
x
K
It means :
Risk of deaths from dis. (X). In POP.
Leading cause of deaths
24
B. Age specific death rate :
No. of deaths ( place – time) for specific age
group from specific dis
=
x
K
x
K
x
K
Total POP. For the specific age group
C. Proportionate mortality rate :
No. of deaths from Dis x ( place – time )
=
Total Deaths ( same place – time)
It means :
– What proportion of death attributed to Dis. X. ?
D. Case Fatality Rate : / Ratio
=
No. of Deaths from Dis x
No. of Cases from Dis x
It means :
– Severity of the Disease .
25
Factors influencing observe
Prevalence Rate
Increased
Longer duration of dis.
Prolongation of life of patients
without cure .
In new cases ( incidence )
In – migration of cases.
Out –migration of healthy
people .
In – migration of susceptible
people.
Improved diagnostic facilities (
better reporting )
Decreased by
Shorter duration of dis.
Case – fatality rate from dis.
In new cases ( incidence )
In – migration of healthy
people
Out – migration of cases
Improved cure rate of cases
26
Relation Between (I), (p)
ex. Using chest x rays, 2000 persons are
screened for T.B, 1000 ( upper income
people) from x area, and 1000 (lower income
people ) from Y area .
Screened
POP.
No.
+ ve x ray
P.R
per 1000 POP.
(I)
Per year
Duration
Y.
1000 ( x area)
100
100
4
25
1000 ( Y area
60
60
20
3
Can we conclude that the risk
of T.B, is high in X than Y area ?
27
Descriptive Epidemiology
Study the distribution of disease within a
population by person, place, and time.
Identify non-random variations in the distribution
of disease to enable an investigator to generate
testable hypotheses regarding etiology.
- Who is getting the disease?
- Where are the rats of disease highest and
lowest?
- When does disease occur commonly or rarely?
28
Descriptive Epidemiology
Describe patterns of disease: (or) distribution of dis. within a
population by person place time.
Person
Who is getting the dis.?
Age, sex, Ethnic status,
Religion, Marital status, occupation, social class,
Education, …
others
Place
where are the rates of dis. Highest and lowest?
Geographical
distribution.
Time
when Does the dis. Occur commonly or rarely?
29
Descriptive Epidemiology
Person
place
time
Who
here
when
Person:
.1 Age:
Most important variable.
Distribution by age group
Or
disease frequency
Explained by:
Susceptibility
Immunity
Exposure
Chronic diseases
30
-
-
by age.
Probability
(Died)
Morality
(Curve)
Age
-
Probability
(Survive)
Survival
Curve
Age
31
-Some dis. Occur exclusively in one
particular age group.
Ex. Ca.Prostate, chronic conditions
by age.
Ex.Aarthritis is, 10 times more
common in 45 – 46 than < 45 years.
Ex.Dental problems by age.
Ex.Skin wrinkling by age skin
elasticity
32
Age specific death Rate
Jordan - 1996
all causes
Total
80
Death 60
Male
Rate/
1000
40
Female
20
0-1 1-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-49 50-54 55-59 60-64 65-69 70-76 75-79
age groups
33
DEATH RATE
50.0
40.0
Developed.
20.0
10.0
Rate/ 5.0
1000 1.0
.05
Developing
<1 1-4 5-14 15-24 25-34 35-44 45-54 55 - 64 65-74 75+
Age groups (y.)
34
%of pop. With limitation of activity - chronic dis.
60
50
40
30
20
10
48
20
20 - 44
45 - 64 65+
Age Groups (y.)
35
2. Gender:
Death Rates higher for Males than
Females.
Sex Linked inheritance.
Difference in hormonal balance.
Environmental … Occupation.
… exposure.
… habit patterns.
Hereditary
36
High Morbidity + Low mortality in F.
May be due to:
- F. seek medical care more freely and at
early stage of dis.
- Dis.
Tend to have less lethal course in
F.than M.
- Expectation of life more in F. than M.
37
Cause of death
M:F Ratio
All causes
1.80
Suicide
3.05
Heart Dis.
2.01
Malignant dis.
1.51
Cerebro – vas. – dis.
1.19
Chronic obst. Lung dis.
3.00
38
Proportionate Mortality Ratio
Jordan 1996
1.Circulatory System Dis
42%
2.Noplasms.
13%
3.Accidants.
11%
4.Conditions in perinatal period
7%
5.Respir. System Dis.
6%
6.Cong. Deformities,
chromosomal abnormality
4%
39
3. Ethnic group [Race] :
- Whites ad non – whites.
- Cancer
Cervix
Breast
Stomach
in blacks.
in whites.
in Japanese.
40
4. Social class:
-
Occupation
Education
}
Area of residence }
Income
}
Total
life
style
Reflect : Nutrition, crowding.
Personal hygiene and Medical Care
Utilization.
41
Mortality R. by social class 70 - 72, U.k, Men aged
15 - 64 IMR by sex:
597
Socal class
Crude
D.R
1.professional
SMR
399
Age st.
D.R
462
77
IMR
M.
F.
14
10
II.Intermendite
skilled
III.Manual,skilled
554
486
81
15
12
580
591
99
17
12
IIII..partly skilled
608
633
106
19
15
1v.Parttly skilled
797
681
114
22
17
v.un skilled
989
832
137
35
27
All men + infant
597
597
100
20
15
42
Relationship between economic status and health care
[ USA children, 6 - 11 years of age, grouped according to family
income ] primary + permanent teeth
Number of teeth
Decayed
Filled
<3000
3-4.9
5-6.9
7-9.9
10-14.9 > 15000
< 3000
3-4.9
5-6.9
7-9.9
10-14.9 > 15000
Family Income (us $ )
economic status + health care USA children 6 – 11 y.
43
5. Occupation:
* Spend 1/3 time
conditions
* Exposure
working in different
affect health.
to:
physical conditions: heat, cold, change atmospheric
pressure, noise / Minining / construction / Diving
ِ/Agriculture /injury and trauma.
chemical : heavy metals (lead, mercury) , CO , So2 ..
Biological : endemic dis.
Occupational stress/jop: (hypertension, peptic ulcer,
diabetes).
44
Exposure to:
Silica
Pul. Fibrosis
Asbestos
mesothelioma, ca. Lung
Aniline dyes
bladder cancer
chromate
Lung cancer
45
6. Marital Status:
for women (sexual exposure, pregnancy,
childbearing, Lactation..)
(Single, married, divorced)
Cancer Cervix: > in married than single women.
Cancer Breast: > in single than married women.
Cancer Breast: > in early age at first pregnancy.
(Protected by Lactation).
46
7.Family Variable:
Family Size.
Birth order.
Present of both parents, or parent.
deprivation.
Maternal age.
Religion of parents.
Position of index person.
47
8. Others:
Immunization.
Habits.
Personality traits: Type A: CHD.
Type B:
CHD.
A B O System:
- Type A
risk of gastric cancer
- Type O
risk of duodenal ulcer
- Sickle cell trait: risk of malaria.
(plas. falciparum.)
48
PLACE
Freq. of dis. can be related to place of
occurrence in terms of areas set off
either by natural barriers as:
mountains, rivers, deserts, and political
boundaries.
Or of certain dis. Due to
particular env., climate,….
Temp., humidity., rainfall, water supply
… etc.
49
- E.g. Tropical diseases.
- Endemic diseases.
- Certain fungal dis.
- Endemic goiter in (iodine def.
areas).
- Mottled dental enamel … fluoride
content of drinking water.
- Melanoma of skin … sunlight.
- Burkitts lymphoma … endemic in
equatorial Africa.
(Epstein – Barr Virus.)
50
Political subdivisions:
Reflect: … water supply, air pollution, vector control,
medical care.
Mapping of Env. Factors:
Water supply, milk routes, school buses, oven, wind
direction, provide a clue about mode of spread.
Comparison:
International
Regional.
:National
Urban
Rural
bedwin
differences reflect(habit)
and reflect (crowding,
Social class)
51
Rural areas: disadvantages:
- Illiteracy.
- Lack of job opportunities.
- Malnutrition.
- Diseases.
- Shortage of medical facilities and medical
personnel.
- Hazards of agricultural work.
- Exposure to pesticides
Urban areas: disadvantages
- Urbanization problems
- Modernization problems. … pollution …
homicide … .. etc..
52
Study of Migrants:
One type of study that attempts to separate genetic from
environmental factors focuses on migrants(comparision of dis. Or
death rates).
e.g.
Japanese
USA
(cancer stomach)
Scottish
N.Z
(C.V.D)
Indians
Gulf states (C.V.D,MI)
Jordanians
Gulf states ( ? ? ? )
53
Diarrhea Mortality Rate / 1000
Population distributed by Governorates:
Ref. UNICEF 1991< 5 y. Survey:
Amman
Balqa
Zarqa
Irbid
Karak
Mafraq
Maan
Jordan
0.00
2.90
0.61
0.00
4.62
0.60
0.00
0.50
54
Geographical areas of highest + Lowest
incidence of selected cancer sites
Ref. R. Doll 1982
Cancer site
incidence
incidence
ratio
Bladder
Colon
Esophagus
Liver
Lung
Uterus
Pancreas
Prostate
Stomach
Ovary
USA
USA
IRAN
Mozamb
England
USA
N.Z
USA(Black)
Japan
Denmark
Japan
Nigeria
Nigeria
England
Nigeria
Japan
India
Japan
Uganda
Japan
6:1
10:1
300:1
100:1
35:1
30:1
8:1
40:1
25:1
6:1
55
Time
 Study of dis. Occur. By time
basic aspect of
epidemiological analysis.
 Occurrence is usually expressed on monthly or
annual basis.
 Major kind of changes with time:
1. Secular trends:
‫ نزعات جيلية‬Long term
Changes over a long period of time, years or
decades. … occur both in infectious and non
infections dis.
‫تبدالت عبر امد طويل من الزمن‬
56
Cancer death rate per 100,000 male
population
colon
Pancreas
60
40
20
0
stomach
30
40
50
60
70
80
90
years
Reflect: - changes in incidence - changes in survival - effect on age
distribution
57
Example: Infectious + Non - Infectious diseases
2)Cyclic Changes: ‫تغيرات فصلية‬
Changes refers to recurrent alterations in the
frequency of dis. Cycles, may be annual (seasonal) or
other periodicity.
e.g. - measles epidemic.
- influenza (A , B ).
- Diarrhea
- infectious + non infectious.
No seasonal pattern in onset of cancer (in general) ….
Exception (melanoma of upper extremities)
Seasonal ….. Drowning, skiing injuries.
58
(Cyclic Trends)
Study of disease occurrence by time during the course of days/
weeks,months,seasons or years.
Ex: R.Tr.Accidants, Measles Epidemic
1
80
150
II
III
170
accident
No
1 a.m
8 a.m
1 pm
hours of the day
4 pm
12 pm
59
Investigation of an epidemic
1.
Verify Diagnosis:
Do clinical, lab., epid. Studies autopsy.
Establish criteria for labeling persons
as cases (symptoms., lab. Or both)
2.
Verify the existence of an epidemic:
Compare current incidence with past levels of
the disease. (epidemic curve, mapping)
60
3) Describe the epidemic: (Person,
Place, Time)
Epidemic curve.
Spot Map.
Calculate Rates …(PAR)…by Age, sex, Occup., exposure to
specific food
4) Formulate and test hypotheses:
Identify type of epidemic; common source+propagated.
Identify the possible source from which disease may
have been contracted.
Compare ill pop. (cases) with well pop. (control) with
regard to exposure to the postulated source.
Calculate R.R for exposed+non exposed persons.
Carry out statistical test to determine probable source.
Confirm epid. Findings by lab. Tests (samples of blood,
feces, suspected food)
61
5) Search for additional cases:
(you have to locate unrecognized or unreproted
cases) by:
Contracting physicians, hospitals or any other
health facilities in the area.
Intensive investigation of a symptomatic persons
or those with mild illness who may be contact of
cases.
6) Analysis of data, interpreting of
findings.
62
7)Management of the epidemic:
Prepare facilities.
Treatment of cases.
Prevention of spread
Immediate control measures.
Permanent control measures.
8) Report the investigation: include:
Discussion of factors leading to the epidemic
Evaluation of measures used for control
Recommendations for prevention of similar episodes in
the future.
9) Continued surveillance
Keep the community under serve. To detect further rise
in incidence and the effectiveness of control measures.
63
R. T. A s by day of the week
17%
16%
10%
S
S.
M
T
W.
T.
F
64
3)Epidemic Pattern
‫النمط الوبائي‬
No
Measles
1979
80 81 82 83 84 85 86 87 88
Years
65
4) Seasonal pattern
‫النمط الموسمي‬
No
‫االسهال‬
Diarrhea
JFMAMJJASOND
1986
1987
Time‫الزمن‬
1988
66
5) Short-term fluctuations:
Found in epidemic of infectious dis. common
source epidemic + Propagated or
progressive epidemic
Clusters by Time + Place :
‫تعنقد او تجمع لمرض او احداث في الزمان والمكان‬
67
changes in dis. Freq. With time .
are represented by

Histograms.
-
-
-
- Frequency polygons.

- Epidemics:
-
* Common source (point source):
-
* Propagated (progressive) epidemic
68
Acute poisoning
40
30
20
10
0
.:
:
:
short:
. period:
5
6
explosive
in no. of cases of the dis. Over ashort period.
.Vigorous public H.measures
.
7
Prevent further consumption
.
.No further cases after 3 days.
8
9
10
Day of month
* exposure of a group of persons to a common, noxious agent.
69
Propagated,
progressive,contagious
300
200
100
0
.
initial rise is less abrupt
Org. propagated in community.
by Pass from person-person
.Cases steadily….. As vacc
campaigns became effective
.
.
.
.
sep
nov
dec
jan
feb
mar
apr
may
Month of year (small pox)
70
‫اذا يختلف شكل المنحنى الوبائي بسبب‬
‫‪ .1‬عدد القابلين لالصابة بالمرض‪(H.Immunity) :‬‬
‫‪(MIP‬‬
‫‪ .2‬فترة حضانة المرض‪MIP) :‬‬
‫كمية المسبب للمرض‬
‫عدوانية المسبب‬
‫قابلية العائل لالصابة‬
‫‪71‬‬
Propagated, progressive,
contagious epidemic
Most often of infectious origin
Result from transmission of infectious
agent from one susceptible host to
another.
Transmission continues until susceptible
depleted.
Examples. (HAV, Small pox).
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* Presence of several peaks
separated in time but within the
I.P. of IHV.
* No. of susceptible is low, or
insufficient contact (exposure
between susceptible and infected
cases.
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