Morbidity Rates Ashry Gad Mohamed Ashry Gad Mohamed Professor of Epidemiology

Objectives At the end of the session students should be able to: 1- calculate and interpret incidence and prevalence rates. 2- Use the attack rate 3- interpret the relation between incidence and prevalence. 10/30/2015prof Ashry Gad Mohamed

Incidence It measures the new cases. It measures the force of infection or disease in the community. IR= No. of new cases during a year / lacality X 10 n Population at risk /year/locality 10/30/2015prof Ashry Gad Mohamed

Example In 1429 the number of breast cancer cases reported to the cancer registry in Riyadh region was 250. The midyear population of Riyadh region was four million. Calculate the incidence of breast cancer in Riyadh. 10/30/2015prof Ashry Gad Mohamed

Females constitute 49% of the population. IR= 250 / 1,960, per 1000 female 1.28 per 10,000 female 12.8 per 100,000 female 10/30/2015prof Ashry Gad Mohamed

Attack rate Acute recurrent diseases e.g. ARTI, food poisoning. Person may catch the disease more than one time. No. of episodes during specified period AR= x k Population at risk/ period 10/30/2015prof Ashry Gad Mohamed

Example: In a village of 600 persons, 1200 visits to the PHCC were due to flu. What is the attack rate of flu in the village? 10/30/2015prof Ashry Gad Mohamed

Factors affect incidence 1- New risk facor Contraceptive pills & thromboembolism. Food additives & cancer New agent HIV & AIDS 10/30/2015prof Ashry Gad Mohamed

2- Changing virulence El-Tor vibrio & cholera. H1N1Influenza virus & influenza pandemic Mycobacteial resistance & TB 10/30/2015prof Ashry Gad Mohamed

3- Changing pattern of intervention Polio eradication & poliomyelitis Chemoprophylaxis & meningitis Environmental sanitation & filth diseases 10/30/2015prof Ashry Gad Mohamed

4-Population pattern Aging & degenerative diseases & cancer 10/30/2015prof Ashry Gad Mohamed

5- Reporting Increase in reporting & incidence Early stage of surveillance & incidence 10/30/2015prof Ashry Gad Mohamed

6-Screening Screening early detection of cases Increase in incidence 10/30/2015prof Ashry Gad Mohamed

7-New diagnostics New diagnostic Increase detection of cases Increase in incidence 10/30/2015prof Ashry Gad Mohamed

8-Selective migration Floods or famines Decrease sanitation Increase susceptable Increase incidence 10/30/2015prof Ashry Gad Mohamed

Prevalence It measures the disease status in the population. Point prevalence: Total cases (old + new) at fixed point of time in place x 10 n total population in the place 10/30/2015prof Ashry Gad Mohamed

Period prevalence Total cases (old + new) during a period of time in place x 10 n total population in the place 10/30/2015prof Ashry Gad Mohamed

example 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. 10/30/2015prof Ashry Gad Mohamed

Factors affecting prevalence 1- Incidence Prevalence = incidence X duration 2- Disease duration Chronic diseases are accumulating so increase the prevalence 10/30/2015prof Ashry Gad Mohamed

3- management programs If successful and curative decrease the prevalence. If only increases the survival without complete cure increases the prevalence 10/30/2015prof Ashry Gad Mohamed

4- Changing classification Blood pressure 140/80 Vs 160/90 Fasting blood sugar 126 Vs /30/2015prof Ashry Gad Mohamed

5-Selective attrition If cases of the disease travel to be treated abroad then the prevalence decreases. 10/30/2015prof Ashry Gad Mohamed

Incidence Vs prevalence incidence Prevalence Cure Death Migration 10/30/2015prof Ashry Gad Mohamed

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Thank You 10/30/2015prof Ashry Gad Mohamed