INTRODUCTION:-The word Morbidity derives from morbid, from Latin word morbidus (“diseased”), from Morbus (“disease”), from the root of Mori (“to die”), or from Proto-Indo-European *mer- (“to rub, pound, wear away”). Morbidity is an essential concept in the health sciences in total and in epidemiology particularly. It is a universal concept that becomes understandable by its operational definition. Morbidity is the occurrence (or frequency) of diseases. So, Morbidity has been defined as ‘any departure subjective or objective, from a state of physiological well-being’.That means the extent of illness, endure, or disability in a definite population. The WHO Expert Committee On Health Statistics noted in its 6th report that morbidity could be measured in terms of three units-
(1) Frequency- Incidence and Prevalence
(2) Duration- Disability Rate
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Use of Morbidity Data:-
(a) Describe the disease load in the community and assist in the establishment of priorities
(b) Provide more comprehensive, accurate, and clinically relevant data essential for basic research.
(c) Monitoring and evaluation of disease control and prevention activities.
Measurement of morbidity:- Three aspects of morbidity are commonly measured by morbidity rate or morbidity ratio, namely frequency, duration, and severity. Disease frequency is measured by incidence and prevalence rates. The average duration per case or the disability per person may serve as a measure of the duration of illnesses. The case fatality rate may be used as an index of severity.
(1)Incidence Rate:- It is one of the important measures of morbidity .it is occurred of an event or characteristic over some time. the incidence rate is defined as,’ the number of new cases occurring in a definite population during a specified period’.
it is given by the following formula:-
Incidence Rate= (No. of new cases of specific disease during a given period / Population at risk during that period) X 1000
For example:- If there had been 500 new cases of an illness in a population of 30000 in a year, the incident rate would be -IR=(500/30000)x 100 =16.7 per the 1000 year. It refers to 17% who reported the new cases out of 1000 population at risk of a particular year. It will be seen from the above definition that incidence rate refers-
(a) Only to new cases.
(b) During a given period (usually one year)
(c) In a specific population or “population at risk”, unless other dominators are chosen.
(d) It can also refer to new spells or episodes of diseases arising in a given period, per 1000 population.
(a) Spells Incidence Rate: - It refers to new spells or episodes of disease arising in a given period, per 1000 population.
For example- a person may suffer from the common cold more than once a year. If he had suffered twice, he would contribute 2 spells of sickness in that year. The formula, in this case, would be:-
Spell Incidence Rate = (No.of spells of sickness starting in a defined period/ Mean no. of persons exposed to risk in the period)×100
(b) Attack Rate:- An attack rate is an incidence rate (usually expressed as a percent), used only when the population is exposed to risk for a limited period such as during an epidemic. The attack rate is given by the formula:-
Attack Rate:= ( No. of new cases of a specified disease during a specified time interval/Total population at risk during the same interval ) X 100
(c) Second Attack Rate:- The number of exposed persons developing the disease within the range of the Incubation period following exposure to a primary case.
For example, in a family of 6 persons, consisting of 2 parents(immune) and 4 children, susceptible to chickenpox, one child develops chickenpox, and after sometimes 2 children develop among three. SAR=⅔ x 100=66%
Use of Incidence Rate:- The Incidence Rate, as a health status indicator, is useful for taking action- (a) To control the disease.
(b) For research into the etiology of preventive and therapeutic measures.
(c) Compare the risk of disease between two and more populations(relative risk).
(d) Since the incidence rate is affected by any factor that affects the development of disease, they can be used to detect etiology.
(2) Prevalence Rate:- All the current cases (old and new) exist at a given point of time, or over some time in a given population. The total number of all individuals who have an attribute or disease at a particular time is divided by the population at risk of having the attribute or disease at this point in time or midway through the period. Prevalence is mainly two types- (a) Point prevalence (b) period prevalence
(a) Point Prevalence(PP):- Point prevalence of a disease is defined as the number of all current cases(old and new) existing at a given point of time about a defined population. The ’point’ in point prevalence, may for all practical purposes consist of a day, several days, or even a few weeks depending upon the time it takes to examine the population sample.
It is given by the following formula:-
It is given by the following formula:-
PP= (No. of all current (old and new)cases of specific disease existing at a given time / Estimated population at the same period) X 100
(b) Period Prevalence(Pp):- It refers to a number of all current(old and new)cases existing during a defined period expressed about a defined population. Period prevalence is given by the formula:-
Pp =(No. of existing (new and old) cases of a specified disease during a given period interval / Estimated mid interval at risk ) x 100
Use of prevalence rate:-
(a) Describe the burden of a disease in a community, thus it is important for health care planners to put and implement effective health programs for the control and prevention of any disease.
(b) Define the rate of clinical characteristics in a subject with a specified disease.
(c) Estimates the probability of having a disease given the result of a diagnostic test result.
(d) Prevalence rates are especially useful for administrative and planning purposes like hospital beds, manpower needs, rehabilitation facilities, etc. The terms incidence and prevalence is illustrated below figure-
Prevalence depends upon 2 factors, the incidence, and duration of illness. Given the assumption that the population is stable, and indices and duration are unchanging, the relationship between incidence and prevalence can be expressed as- P=I x D Where, P=prevale, I=incidence D=mean duration
For example:-supposed Incidence=10 cases per 100 population per year; Mean duration of disease=5 years. So, P=10 x 5=50 per 1000 population .
Conversely, it is possible to derive incidence and duration as follow: -
Incidence= P/D Duration=P/I
Causes of Morbidity:- Heart disease, cancer, chronic lower respiratory diseases, stroke, Alzheimer's disease, diabetes mellitus, pneumonia and influenza, kidney disease and suicide accounted for almost 75% of deaths in the U.S. in 2013. Seven of the 10 leading causes of death are chronic diseases. Two, heart disease and cancer, account for nearly half of US deaths each year. The prevalence of chronic disease remains steady, but infectious disease has had an uptick in recent years thereby increasing morbidity. In addition to infectious diseases, foodborne illness, associated infections and sexually transmitted diseases also contribute to higher morbidity among Americans.
Importance of morbidity:-
(a) It describes the nature and extent of the disease load in the community and thus assists in the establishment of priorities
(b) It helps as the starting point for aetiological studies, and thus plays a crucial role in disease prevention.
(c) They are needed for monitoring and evaluation of disease control activities.
(d) It usually provides more comprehensive and more accurate and clinically relevant information on patient characteristics.
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