CHAPTER 2
MEASURES OF MORBIDITY AND MORTALITY
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SOURCES OF
INFORMATION ON
POPULATION’S HEALTH
2
Surveillance can be defined as
the ongoing, systematic, collection of data related to health events;
their verification, analysis, interpretation,
and the dissemination of information to those who need to know
in order to reduce morbidity and mortality and to improve health.
A. Surveillance system: Definition
Source: Thacker SB (2000). In: Principles and Practices of Public Health Surveillance. Oxford University Press, New York. 1–16.
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A. SURVEILLANCE SYSTEMS
OBJECTIVES
Measure and
monitor diseases
burden
• To describe disease occurrence by time, place and
person
• To monitor trends of disease over years
• To measure incidence, prevalence and mortality
rates
• To identify high risk populations or areas
Detect outbreaks
and alerts
• To confirm and investigate outbreaks
• To find etiologies, modes of transmission and
sources of infection
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A. Surveillance system
Lebanon
Legislations
Official laws: law on Communicable diseases issued on
the 31st December 1957.
Regulations:
▪
Reporting Forms
▪
Case definition: common understanding by
professionals for targeted diseases/events. Based on
clinical, epidemiological, laboratory and other
paraclinical findings:
Confirmed / Probable / Suspected
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Immediately notification
Acute Polio/Acute Flaccid Paralysis
Cholera
Creutzfeld Jakob Disease
Diphtheria
Food Poisoning
Hemorrhagic fever
Novel Influenza viruses
Malaria
Meningitis
Measles
Neonatorum tetanus
Plague
Rabies
Rubella / CRS
Smallpox
Typhus
Yellow fever
Unusual event
Weekly notification
Bilharzia
Brucella
Dysentery
Gonorrhea
Hepatitis Viral A, B, C, D, E
HTLV1
HIV
Leishmania
Leprosy
Mumps
Parasitic Worms
Pertussis
Syphilis
Tetanus
Tuberculosis
Trichinella
Typhoid fever
A. SURVEILLANCE
SYSTEM
MANDATORY
NOTIFIABLE
DISEASES IN
LEBANON
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A. Surveillance system in Lebanon
Data collection and reporting
Central
Disease
notificatio
n
Fax
Province
Mail
e
tur
Fu
Private
physicians,
Hospitals,
Dispensaries, Schools
District
Electroni
c
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A. Surveillance system in Lebanon
Data analysis and reporting
Data management, analysis and
reports
Dissemination of information:
☞www.moph.gov.lb
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B. Registry
Registry can be defined as:
A database gathering information about cases diagnosed with a particular type of disease.
Collected information usually includes diagnostic, treatment and outcome information,
and sometimes survival/death
Example: cancer registry, diabetes, cardiovascular disease, congenital malformations …
Cancer registry in Lebanon:
☞http://www.moph.gov.lb/Prevention/Surveillance/documents/DF2007.htm
☞ http://www.moph.gov.lb/Prevention/Surveillance/documents/DM2007.htm
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C. DEATH CERTIFICATES
Underlying
Intermediate
Immediate
ICD10
code
AIDS-HIV
infection
(6 years)
AIDS-associated
nephropathy
(7m)
Acute renal
failure (4d)
B20.0
Heavy
cigarette
smoking (35
years)
Chronic
bronchitis (10
years), Acute
bronchitis (4
years)
Severe
obstructive
airway
disease (18
hrs)
Z72.0
Death certificates give valuable
information regarding mortality in the
population, but also the cause of death
In many countries, standard death
certificates record the
underlying/intervening/immediate cause
of death
Causes are classified according to the
“International Classification of
Diseases”
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C. Death certificate
Lebanese form
Immediate cause:
Disease or complication that directly
resulted in death
Intervening cause(s) :
Other conditions that contributed to
death and are a result of underlying
cause
Underlying cause(s) :
Disease, injury that initiated the train
of morbid events leading directly to
death
Associated cause(s) :
All other diseases and conditions that
were present at time of death, and may
have contributed to it, but did not lead
to underlying cause
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Source: Kircher & Anderson. Death Certificates. JAMA, July 17 1987, Vol 258, No 3
Usefulness of mortality data:
C. DEATH
CERTIFICATES
USEFULNESS
AND
LIMITATIONS
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• Assessing the burden of disease
• Tracking changes in disease severity over
time
Limitations:
• Completeness in filling the death
certificates
• Accuracy in assigning the underlying cause
of death
• Error or inconsistency in coding causes of
death
• Representativeness in registering the death
certificates
D. Census
Census can be defined as:
Enumeration of individuals within a population, with details of demographic
data (such as age, sex,…)
Last census was conducted in Lebanon in 1932
National-scale studies are conducted instead (national household surveys)
☞www.cas.gov.lb
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E. Other sources of information
Hospitals admissions and discharge summaries:
•
Information that can be collected: Reason for hospitalization, medical and
laboratory testing, medical procedures and treatment provided,
condition of patient on discharge
•
Limitations: Are not representative, may not be completely filled
Epidemiologic Studies:
•
Collect information about health outcomes, exposure variables and
confounding factors
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SOURCES OF HEALTH INFORMATION ALLOW US TO
ANSWER THE FOLLOWING QUESTIONS
How many individuals are currently living with the health outcome?
How many new cases are occurring?
Calculating Measures of morbidity
How many deaths occurred in the population?
How many deaths occurred in the population because of a certain disease in
the population?
Among cases diagnosed with a certain disease, how many are dying?
Calculating Measures of mortality
Mortality and morbidity measures rely on :
Count, Ratio, Proportions and Rates
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CALCULATING
MEASURES OF:
COUNTS
RATIO
PROPORTION
S
RATES
MORBIDITY
&
MORTALITY
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COUNTS
• Number of cases
“we have 5 cases of tetanus”
Simple / most frequently performed measure in epidemiology
- Refers to the number of cases of a disease e.g. (or other health
phenomenon)
- Limited usefulness for epidemiologic purposes without knowing size of
the source population
Very little information
What, who is in the denominator ?
RATIO
•
•
•
The division of 2 numbers
Numerator NOT INCLUDED in the denominator
Allows to compare quantities of different nature
Example: Number of nurses per Physician
= 5 / 2 = 2.5 / 1
2.5 nurses per 1 physician
Proportion
•
•
•
•
•
The division of 2 numbers
Numerator always included in the denominator
Quantities have to be of same nature
Proportion always ranges between 0 and 1
Percentage = proportion x 100
3
--- = 0.6 = 60%
5
Example: Proportion
• Proportion of injecting drug users (IDU) among
cases of tetanus in the UK
– 141 cases of tetanus, 2 IDU
– Percentage of IDUs among cases of tetanus is
2/141 = 0.014 = 1.4%
Rate
• The division of 2 numbers
• Speed of occurrence of an event over time
Numerator
- number EVENTS observed for a given time
Denominator
- POPULATION (+ observation time)
Observed in 2008
2
----- = 0.02 / year
100
Example: rate
• Mortality rate of tetanus in France in 1995
– Tetanus deaths: 17
– Population in 1995: 58 million
– Mortality rate 17/58x106 = 0.29 per 1,000,000 per
year
• Rate may be expressed in any power of 10
– 100; 1,000; 10,000; 100,000; 1,000,000
IDENTIFY THE COUNT, RATIO, PROPORTION AND RATE
Hypothetical data
In 2012, it was estimated that 1.4 million people, which includes 190,000 children,
are living with HIV in Uganda. An estimated 62,000 people died from AIDS in
2011 and 1.1 million children have been orphaned by Uganda's devastating
epidemic.
It was estimated that there are 5,7 males living with HIV/AIDS for every 1 female
(living with HIV/AIDS).
In a survey conducted in Uganda that year concluded that only 39 percent of
young people aged 15 to 24 know all the necessary facts about how HIV can be
prevented, suggesting a lack of clear sex education.
From 1980 to 2013, the crude incidence of HIV/AIDS increased from 3.3 to 7.1
per 1000 population.
MORBIDITY AND MORTALITY
MEASURES
Morbidity measures
Mortality measures
• Prevalence
• Incidence
•
•
•
•
Crude-mortality rate
Specific mortality rate
Proportionate mortality
Case-fatality rate
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MORBIDITY MEASURES:
PREVALENCE
Estimates the proportion of people having the disease (or health
outcome) in the population at a defined time
The numerator includes people “living with the disease” during the
specified time
The date onset of disease is not determined, and hence subjects in
numerator have different disease durations
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MORBIDITY MEASURES:
PREVALENCE
Two types of prevalence:
Point prevalence: “Do you currently have hypertension?”
How much of a particular disease is present in the population at a
single point in time?
Period prevalence: “Have you had hypertension during the last
(n) years?”
How much of a particular disease is present at the population over
a longer period?
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EXERCISE: FOR EACH OF THE FOLLOWING FACTORS, INDICATE
HOW IS THE PREVALENCE AFFECTED (INCREASE, DECREASE)?
Cases are living with the disease, not cured?
Disease is rapidly fatal?
Cases are being cured because of an improved treatment?
Cases are better detected/reported due to improve facilities?
New “cases” are coming to the population?
“Healthy people” are migrating out of the population?
Short duration of a disease?
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ANSWER:
PREVALENCE
IS…
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MORBIDITY AND MORTALITY
MEASURES
Morbidity measures
Mortality measures
• Prevalence
• Incidence
•
•
•
•
Crude-mortality rate
Specific mortality rate
Proportionate mortality
Case-fatality rate
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MORBIDITY MEASURES:
INCIDENCE
Incidence rate =
Number of new cases over a time
period
× multiplier (e.g., 100,000)
Average population at
risk
Measure the risk of getting the disease in a specified period of time
The numerator includes the cumulative number of new cases, identified
during the specified period of time
The denominator includes the population at risk of the health outcome
during the specified period of time
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INCIDENCE & PREVALENCE MEASURE DIFFERENT
ASPECTS OF DISEASE OCCURRENCE
Prevalence
Incidence
Numerator
All cases no
matter how
long diseased
Only NEW
cases
Measures
Presence of
disease
Risk of
disease
Most useful
Resource allocation
EXAMPLE
In 2015, Lebanon counted 4,650,784 subject
Among them 500,471 were living with Diabetes. Of those living with diabetes
15,000 were newly diagnosed
Calculate
Prevalence of diabetes
500471/4650784 = 0.1076 = 107 per 1000 person
Incidence of diabetes
15000/4650784 = 0.00322= 3.2 per 1000 person
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Relationship between prevalence &
Incidence
Prevalence is affected by both disease Incidence and duration
duration: - introduction of new treatment
- enhanced recovery and death prevention
duration: rapid recovery, rapid death
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MORBIDITY AND MORTALITY
MEASURES
Morbidity measures
Mortality measures
• Prevalence
• Incidence
•
•
•
•
Crude-mortality rate
Specific mortality rate
Proportionate mortality
Case-fatality rate
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MORTALITY RATE:
CRUDE MORTALITY RATE
•
The numerator includes the number of deaths of all causes, in all age and
sex groups
•
The Crude Mortality Rate does not take into consideration that the risk of
dying varies by age, sex, cause of death…
•
More specific mortality rates are calculated
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MORBIDITY AND MORTALITY
MEASURES
Morbidity measures
Mortality measures
• Prevalence
• Incidence
• Crude-mortality rate
• Specific mortality rate
• Proportionate
mortality
• Case-fatality rate
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MORTALITY RATE:
SPECIFIC MORTALITY RATE
•
Age-specific rates
Number of deaths in age group X during a specified year
Total population of age group X during the same year
•
Sex-specific rate
Number of deaths in sex group X during a specified year
Total population of sex group X during the same year
•
(x10n)
Cause-specific rates
Number of deaths due to cause D during a specified year
Total population during the same year
•
(x10n)
(x10n)
Age-cause-specific rates
Nb. of deaths in age group X due to cause D during a specified year
Total population of age group X during the same year
(x10n)
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EXERCISE: CRUDE AND SPECIFIC MORTALITY
RATES
In 2009, a total of 23,480 people have died in Lake House City.
Of total deaths in 2009, 1450 were under five years old.
Knowing that in 2009:
-
The mid-year population of Lake House City was: 7 510 940.
The mid-year under five (under-5) population of Lake House
City was 23 450.
Calculate:
-
The crude mortality rate
-
The under-five specific mortality rate
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ANSWER:
The crude mortality rate:
=23 480/7 510 940
or 3 deaths per 1000 population 2009 in Lake-House City
The under-five specific mortality rate:
=1450/23 450
or 6 deaths per 100 child under-5 in 2009 in Lake-House
City
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MORBIDITY AND MORTALITY
MEASURES
Morbidity measures
Mortality measures
• Prevalence
• Incidence
•
•
•
•
Crude-mortality rate
Specific mortality rate
Proportionate mortality
Case-fatality rate
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PROPORTIONATE MORTALITY
• Indicates the proportion of deaths due to a specific disease
• Allows identifying the leading cause of death in the population
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MORBIDITY AND MORTALITY
MEASURES
Morbidity measures
Mortality measures
• Prevalence
• Incidence
•
•
•
•
Crude-mortality rate
Specific mortality rate
Proportionate mortality
Case-fatality rate
42
CASE FATALITY RATE
• Indicates the proportion of deaths among cases of a specific diseases
• Allows identifying trends of disease severity
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EXERCISE: PROPORTIONATE MORTALITY AND
CASE FATALITY RATE
In 2009, in Lake House City, 540 cases of severe acute
respiratory infections were reported in 2009. Among these
cases, 26 deaths occurred.
Knowing that in 2009:
-
The mid-year population of Lake House City was: 7 510 940.
-
The total deaths registered was: 23 480
Calculate:
-
The proportionate mortality for SARI
-
The case-fatality rate for SARI
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ANSWER:
The proportionate mortality:
26/23480=0.0011=0.11%
0.11 per 100 deaths are due to severe acute respiratory
infections in LHC in 2009
The case-fatality rate:
26/540=4.8%
4.8 deaths per 100 SARI cases in LHC in 2009
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KEY NOTES
Several sources provide valuable information on health
Some sources routinely collect information, other (like epidemiological
studies) collect information for the purpose to answer specific research
questions
Measures of occurrence (Morbidity and Mortality) provide valuable
description for the health profile of the population
Need to identify numerator
Need to determine population size (denominator)
When comparing rates (incidence or mortality) in different populations, we
can no longer use the crude mortality rate.
Use standardized (or ageadjusted rates)
Adjustment can also be made for sex, race,…
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