Tutorial Morbidity 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= = 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.