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.