tutorial morbidity rates
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TutorialMorbidity Rates
Dr.Nouf ALTurki
Dr.Koloud ALTassan
LEARNING OBJECTIVE
• Define and calculate measure of frequency of disease occurrence (Prevalence rate, Incidence rate, Attack rate).
• Be able to decide when to use them.
• Be able to interpret the results.
Prevalence
• It measures the status of the disease in the population.
• Point Vs Period.
• Use of Prevalence:
Situation analysis.
Useful in health care settings e.g. estimate services required.
Cannot study cases of rapid cure or died.
• MOH conducted a survey for RVF among workers in slaughterhouses in Makkah. 224 seropositive workers were identified among 6000 workers. Calculate the prevalence of RVF?
• No. of prevalent cases=224• No. persons in the pop.= 6000
• Therefore, the prevalence= 224/6000 X1000=37.3/1000
EXERCISE
• Parents of 900 children in AlKharj were asked if their children have developed diarrhoea during the past 3 weeks. 300 children had a positive history of diarrhoea.
• Calculate the prevalence? e.g: Period
• No. of cases = 300• No. of population = 900• Prevalence = 300/900 X 100 = 33/100
EXERCISE
Incidence rate
• Use of Incidence:
It measures the Force of infection or disease in the community.
Useful for investigating causal relationships and risk factors.
EXERCISE • In 1426 the number of breast cancer
cases reported to the cancer registry in Riyadh region was 200. The midyear population of Riyadh region was four million.
• Calculate the incidence of breast cancer in Riyadh.
• In 1426 the number of breast cancer cases reported to the cancer registry in Riyadh region was 200. The midyear population of Riyadh region was four million. (2.1 male,1.9 female)
• Calculate the incidence of breast cancer in Riyadh?
• No. of new Br. Ca. cases=200• No. of persons at risk of Br. Ca =1.9 million• The incidence of developing Br. Ca. in Riyadh=
200 / 1,900,000 X 100,000= 10.5/100,000
Attack Rate
• is a variant of an incidence rate, applied to a narrowly defined population observed for a limited time, such as during an epidemic.
• Use of Attack Rate
• Acute recurrent diseases e.g. ARTI, food
poisoning. (Person may catch the disease more than one
time).
• Distinguish between case and an episode
- Case e.g. Poliomyelitis.
- Episode e.g. an asthma attack requiring admission. better to use Attack Rate
EXERCISE
• In a village of 600 persons, 1200 visits to the PHCC were due to flu. What is the attack rate of flue in the village?
• No. of the people in a village = 600
• Illness = 1200
• Attack rate=(1200 ÷ 600 ) X 100
=200%
• In a university student has got H1N1 flu. She attended a class of 80 students, of which 12 students got the flu 5 days later.
• Calculate the attack rate of the flu.?
Class = 80
ILL :• new cases= 12• old case = 1• At risk students= 80 - 1 = 79
Attack rate = (12 ÷ 79) X 100
= 15%
EXERCISE
Quiz
Mention the relation between incidence and prevalence rate (equation)
MCQ
• The main use of incidence rate is:
a. For situation analysis .
b. Measures the force of infection or disease in the community.
c. For allocation of resources.
d. To assess an epidemic disease.
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