Assessing the occurrence of disease: morbidtiy and mortality Flashcards
Global Burden of Disease
Study that was used to predict the future burden of disease.
Study examined mortality data and impact of premature death and disability on a population
Disability adjusted life year
Index that combined factors in global burden disease
What is a cohort?
A group of people who share the same experience
Differences in mortality over time or between populations may be:
Artificial or real
Artificial
numerator: errors in diagnosis, errors in age, changes in coding rules, changes in classification
denominator: errors in counting population, errors in classifying by demographic, errors in characteristics (age,sex, race) and differences in % of population at risk
Real
change in survivorship w/out change in incidence
change in incidence
change in age composition of the population
a combination of the above factors
Standardized mortality ratio (SMR)
resultant ratio from indirect age adjustment calculation
= observed no. of deaths per year/ expected no. of deaths per year
Mortality increases with old age
What are the two approaches used to account for age differences in two populations
Direct age adjustment
Indirect age adjustment
Direct age adjustment
a hypothetical standard population is created. This is then used to reduce the effects of any age differences between two or more populations being compared.
Indirect age adjustment
The no. of expected deaths in each age group in the population of interest is calculated and added together. The no. of deaths that were actually observed in the same population are likewise added together.
Problems with mortality data
most of the info comes from death certificates. On death certificates, deaths are coded according to underlying cause of death. Unfortunately the underlying cause of death does not contain info on the immediate cause of death or contributing causes of death
Why consider mortality?
It is an index of severity and risk of a disease. Is only a good measure of risk or incidence of disease when: case fatality is high and duration of disease is short
Morbidity: disease is mild and not fatal good incidence of disease
Years of potential life lost
measure of premature mortality or death reference age= 85 85-20=65 85-80=5 95-50=35 total=105YPLL
What are the two steps used to calculate years of potential life lost
1: for each cause, each deceased persons age at death is subtracted from the predetermined age of death ( generally 65 years)
2: The YPLL for each individual are then added together to yield the total YPLL for a specific disease
Proportionate mortality
ratio: no. of deaths from a specific cause per 100 or 1000 deaths from all causes in the same period
Gives indication of major cause of death
Formula for proportionate mortality
no. of deaths from certain disease/ total deaths overall
Case fatality rate
measure severity of disease
date of diagnosis used as surrogate for date of disease onset
Formula for case fatality rate
no. of people who die during a period after disease diagnosis or onset/ no. of people with the specific disease x1000
What is the difference between case fatality and mortality?
denominator of mortality represents the entire population at risk of dying from the disease including those who have and don’t have the disease ( but at risk of developing the disease.
the denominator of case fatality is limited to those who already have the disease. Can be used to measure any benefits of new therapy
as therapy improves, case fatality would be expected to decline
Why is mortality of great interest:
- can be used to indicate severity of disease and provide info on whether treatment has become less or more efficient
- can identify diff in the risk of dying from a disease between people in diff geographical areas and subgroups in a population
- mortality rates can be used instead of incidence rates when disease being investigated is lethal and severe
What information is gathered during disease surveillance?
- morbidity
- mortality
- infectious disease patterns
- non-infectious disease patterns
- completeness of vaccination coverage
- levels of environmental risk factors for disease
What is the relationship between incidence and prevalence?
Incidence is a measure of risk and prevalence is not since it does not that into consideration the duration of the disease
Prevalence= incidence x duration of
prevalence depends on incidence rate and duration of disease disease
Problems with hospital data
1- Hospital admissions are selective in relation to
- personal characteristics
-severity of disease
-associated conditions
-admission policies
2- records are not designed for research but for patient care
they may be:
-incomplete, illegible or missing
-variable for diagnostic quality (records of hospital, physicians and clinical services may differ)
Problems with measure of incidence and prevalence
NUMERATOR
-defining who has the disease
-deciding which people should be included in the numerator owing to possible sources of error in data gathering or differences in classification
DENOMINATOR
-classifying individuals into certain population groups is not always clear
- everyone represented by the denominator must have the potential to enter the group represented by the numerator
Prevalence
measure how commonly a disease occurs in a population
measure of burden of disease
Formula for prevalence
no. of cases of a disease present in the population at a specified time/ no. of persons in the population at that specified time x1000
Two types of prevalence
point - no. of people with the disease at a specified time
period- how many have had the disease at any point during a specified period
Incidence
no. of new cases of a disease that occur in a population in a given period
Formula for incidence rate
no. of new cases occurring during a given period/ no. of people at risk during the same period x1000
Denominator ( no. of people at risk can be calculated in two ways) incidence
- all people at risk are observed throughout the entire period and their disease status recorded
- not all people at risk are observed for a full period. If diff people are monitored for diff periods, then the denominator is calculated by taking the sum of the units of time that each person at risk was monitored. This is called person time
Equation for person time
no. of new cases occurring during a given period/ total person time( sum of the periods of observation for each person x1000
Attack rate steps
attack rate is a proportion rather than a rate and time is specified
1- screening for prevalent cases at baseline
-identify population
-determine who has and who does not have the disease
-follow up on only those who did not have the disease at baseline
2- follow up and rescreening at 1 year to identify cases that developed during the year
-follow up on those who did not have the disease at baseline
-follow up the population at 1 year ( developed and did not develop)
Morbidity
occurrence of disease in a population described using the rates and proportions
Occurrence of disease can be measured using
Rates- how fast the disease id occurring in a population
Proportions- what fraction of the population is affected
Sources of data used to obtain info about a sick person
- hospitalization, medical and hospital records
- primary care providers records
- patient using interviews or questionnaire
- family member or anyone familiar with patients health –status
- health insures
Why surveillance in developing countries may present additional problems?
- difficult to reach areas
- difficult to maintain communication to central authorities
- definitions of disease used may be different
Active surveillance
Active Surveillance:
- project staff are specifically recruited to carry out a surveillance program
- they are recruited to make periodic visits to health care facilities ( clinics and hospitals) to identify new cases of diseases or deaths from disease that have occurred (case finding)
- may involve interviewing patients and physicians, reviewing medical records, surveying villages and towns for cases either periodically or routinely or after an index case
- more accurate because individuals have been employed and trained to carry out this responsibility
- more expensive to maintain often more difficult to develop than passive
Passive surveillance
Passive surveillance :
-use of available data on reportable diseases-disease reporting requested by government or local health authority
-responsibility for reporting often fall on health care provider or district officer ( passive reporting)
completeness and quality of data reported depends
on this individual and his/her staff
-often no additional funds or resources
Problems with passive surveillance
- underreporting
- lack of completeness
- staff overburdened by their primary responsibilities of providing health care
Benefits of passive reporting
- inexpensive and easy to develop
- allows for international comparisons
Surveillance case
set of uniform criteria used to define a disease for public health
-aids public health officers in recording and reporting cases
Surveillance
ongoing systematic collection , analysis and interpretation of health data essential to the planning, implementation and evaluation of public health practice closely integrated with the timely dissemination of these data to those who need to know
Why surveillance is carried out?
- monitor changes in levels of risks for specific diseases
- monitor changes in disease frequency
- monitoring changes in congenital malformations, noncommunicable diseases, environmental toxins, injuries ad illness after natural disasters e.g. hurricane and earthquake
- monitor completeness of vaccination coverage
- prevalence of drug resistant organisms e.g. malaria and drug resistant TB
- protection of population
Mortality
no. of people who died in a population
Info to calculate frequency of morbidity and mortality comes from
- hospital records
- physician records
- interviews with patients
- medical aid records
- death certificates
