Morbidity Rates 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. 2/16/2022 prof 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 2/16/2022 prof 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. 2/16/2022 prof Ashry Gad Mohamed

Females constitute 49% of the population. • • • IR= 250 / 1, 960, 000 0. 000128 0. 128 per 1000 female 1. 28 per 10, 000 female 12. 8 per 100, 000 female 2/16/2022 prof 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= xk Population at risk/ period 2/16/2022 prof 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? 2/16/2022 prof Ashry Gad Mohamed

Factors affect incidence 1 - New risk facor Contraceptive pills & thromboembolism. Food additives & cancer New agent HIV & AIDS 2/16/2022 prof Ashry Gad Mohamed

2 - Changing virulence El-Tor vibrio & cholera. H 1 N 1 Influenza virus & influenza pandemic Mycobacteial resistance & TB 2/16/2022 prof Ashry Gad Mohamed

3 - Changing pattern of intervention • Polio eradication & poliomyelitis • Chemoprophylaxis & meningitis • Environmental sanitation & filth diseases 2/16/2022 prof Ashry Gad Mohamed

4 -Population pattern • Aging & degenerative diseases & cancer 2/16/2022 prof Ashry Gad Mohamed

5 - Reporting • Increase in reporting & incidence • Early stage of surveillance & incidence 2/16/2022 prof Ashry Gad Mohamed

6 -Screening early detection of cases Increase in incidence 2/16/2022 prof Ashry Gad Mohamed

7 -New diagnostics New diagnostic Increase detection of cases Increase in incidence 2/16/2022 prof Ashry Gad Mohamed

8 -Selective migration Floods or famines Decrease sanitation Increase susceptable Increase incidence 2/16/2022 prof 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 total population in the place 2/16/2022 prof Ashry Gad Mohamed n

• Period prevalence Total cases (old + new) during a period of time in place x 10 total population in the place 2/16/2022 prof Ashry Gad Mohamed n

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. 2/16/2022 prof Ashry Gad Mohamed

Factors affecting prevalence 1 - Incidence Prevalence = incidence X duration 2 - Disease duration Chronic diseases are accumulating so increase the prevalence 2/16/2022 prof Ashry Gad Mohamed

3 - management programs • If successful and curative decrease the prevalence. • If only increases the survival without complete cure increases the prevalence 2/16/2022 prof Ashry Gad Mohamed