 Measures of Morbidity Dr. Asif Rehman

Measurements of Morbidity  Epidemiology: The study of the distributions and determinants of health related states or events in specified population and the application of this study to control health problems. (Leon Gordis, 5 th edition)

Measurements of Morbidity Specific objectives of epidemiology ?  Cause of the disease  Distribution/frequency of the problem  Natural history and prognosis  Evaluate both existing and new preventive and therapeutic measure and modes  To provide foundation for developing public policy

Measurements of Morbidity Morbidity:  Morbidity has been defined as “any departure, subjective or objective, from a state of physiological well being”  The term is used equivalent to such terms as sickness, illness, disability etc. (K Park, 20 th edition)

Measurements of Morbidity Three aspects of morbidity are commonly measured by morbidity rates or ratios namely:  Frequency (measured by (Incidence & Prevalence)  Duration (measured by average number of days of (Disability/person)  Severity (Case Fatality rate) may be used as an index of severity)

Measurements of Morbidity  Data on Morbidity; why it is useful: Many diseases with a low case fatality e.g mental illnesses, musculoskeletal diseases, rheumatoid arthritis, chicken pox and mumps. In this situation, data on morbidity (Illness) are more useful than mortality rates. (R Bonita WHO, Basic epidemiology, 2 nd edition)

Measurements of Morbidity

For example: If there had been 500 new cases of an illness in a population of 30,000 in a year, the incidence rate would be: 500/30,000 X 1000 = 16.7 per 1000 Note: the incidence rate must include the unit of time used in the final expression. If you wrote 16.7 per 1000, this would be inadequate. The correct expression is 16.7 per 1000 per year.

Measurements of Morbidity Special incidence rates  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 of time such as during epidemic.  Secondary attack rate The number of exposed person developing the disease within the range of the incubation period following exposure to a primary case.

Measurements of Morbidity Secondary attack rate Suppose there is a family of 6 consisting of 2 parents (already immune) and 4 children who are susceptible to a specific disease, say Measles. There occurs a primary case and with in a short time 2 secondary cases among the remaining children. The secondary attack rate is SAR = No of exp ppl developing disease within range of I.P X 100 Total no of exp ppl 2/3 X 100 = 66 per 100. Here a primary case is excluded from both numerator and denominator.

Measurements of Morbidity Uses of incidence rate: The incidence rate, as a health status indicator, is useful for taking action,  To control a disease  For research into etiology and pathogenesis, distribution of disease and efficacy of preventive and therapeutic measures. For instance if the incidence rate is increasing it might indicate failure or ineffectiveness of the current control programs. And suggest the need for a new disease control program.

Measurements of Morbidity Prevalence  The term “disease prevalence” refers specifically to ALL CURRENT CASES (old and new) existing at a given point in time or over a period of time in a given population. (K Park, 20 th edition)

Measurements of Morbidity Prevalence is of two types  Point Prevalence  Period prevalence

Measurements of Morbidity Point Prevalence: It is defined as number of all current cases (old and new) of a disease at one point of time, in relation to a defined population. The point in a point prevalence, may for all practical purposes consists of a day, several days or even a few weeks depending upon the time it takes to examine the population sample. PP = no of all cases (old & new) of a specified disease existing at a given point in time X 100 Estimated population at the same point in time

Measurements of Morbidity Period Prevalence: A less commonly used measure of prevalence is period prevalence. It measures the frequency of all current cases (old and new) existing during a defined period of time. e.g (Annual Prevalence) expressed in relation to defined population. It includes cases arises before but extending into or through to the year as well as those cases arising during the year. Period P = no of all cases (old & new) of a specified disease during a given period of time interval X 100 Estimated mid interval population at risk

Measurements of Morbidity Uses of prevalence:  Prevalence helps to estimate the magnitude of health/disease problem in the community, and identify potential high-risk population  Prevalence rates are specially useful for administrative and planning purposes e.g. hospital beds, manpower needs, rehabilitation facilities etc (K Park, 20 th edition)

Measurements of Morbidity

Disability Adjusted Life Years (DALYs) One DALY = One lost year of healthy life DALYs for a disease are sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition DALY = YLL + YLD

Exercise  Population of city of East London on March 30 th, 2003 is 183,000. Number of new active cases of Tuberculosis occurring between Jan 1 st and June 30 th, 2003 is 26. Number of active TB cases according to the city register on June 30 th, 2003 is 264  Calculate the incidence rate of active TB for the 6 months period ?  Calculate the Prevalence rate of active TB as of June 30 th, 2003?

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