1. g PATH216 INTRODUTION to GENERAL EPIDEMIOLOGY Mohamed M. B. Alnoor

2. EPIDEMIOLOGY CONTENTS  Definition of EPIDEMIOLOGY  Other Definitions TIME - PLACE - PERSON  Morbidity Rates Incidence rate Attack rate Prevalence rate  Determinants of disease  Distribution of Disease  Branches of community medicine

3. EPIDEMIOLOGY What is Epidemiology? Epidemiology is the Study of distribution and determinants of health- related states and events In specified populations and application of this study to control health problems. distribution and determinants

4. EPIDEMIOLOGY What is Epidemiology? distribution and determinants

5. EPIDEMIOLOGY What is Epidemiology? Distribution of Disease WHEN Time WHERE Place WHO Person

6. EPIDEMIOLOGY Distribution of Disease Time Changing or stable Cyclic Seasonal secular

7. EPIDEMIOLOGY Distribution of Disease Place Geographic -Restricted/Wide spread -Coastal/inland Weather(temp., humidity, rainfall) Altitude/latitude/longitude Urban/rural

8. EPIDEMIOLOGY Distribution of Disease Person Age Sex Race Education Occupation behavior

9. EPIDEMIOLOGY Distribution of Disease Distribution of disease is quantified as morbidity rates : i.e. the extent of illness, injury or disability in a defined population MORBIDITY : Any departure ((subjective or objective )) (physiological or psychological) from state of well being

10. EPIDEMIOLOGY Distribution of Disease Distribution of disease is quantified as morbidity rates : occurrence time period population group Rate : a measure of the occurrence of a health event in a population group at a specified time period numerator denominator Number of events in time period Number at risk for the event :

11. EPIDEMIOLOGY Distribution of Disease Injury Deaths, Australia, 1992

12. EPIDEMIOLOGY Distribution of Disease Injury Death Rates, Australia, 1992

13. EPIDEMIOLOGY Distribution of Disease Injury Death Rates, Australia, 1992 Injury Deaths, Australia, 1992

14. EPIDEMIOLOGY Distribution of Disease morbidity rates Why are rates useful?  Can help to identify High-risk Groups (groups with an elevated risk of disease). these groups can be studied to identify “risk factors”  Provides a basis for making valid comparisons of health events by considering the number at risk in each population.  Morbidity rates are used as indicators of health

15. EPIDEMIOLOGY Distribution of Disease morbidity rates Distribution of disease is quantified as morbidity rates :  Incidence rate  Attack rate  Prevalence rate

16. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Number of new cases during a year in a locality Population at risk / year/locality = Incidence rate 1O n  It involves only the new cases.  It measures the probability that healthy people will develop disease during a specified period of time X

17. EPIDEMIOLOGY Distribution of Disease morbidity rates  The numerator is new cases  The denominator may change over time as people develop disease  However, in practice  in large studies, the denominator is often the mid- year population  in small studies, the denominator includes persons at risk of the disease Incidence rate

18. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate From October 1, 1990 to Sep 30, 1991?

19. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate From October 1, 1990 to Sep 30, 1991? 4 4/14

20. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate From October 1, 1990 to Sep 30, 1991? 4 4/20

21. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Example In 2009 the number of breast cancer cases reported to the cancer registry in Riyadh region was 250 cases. The midyear population of Riyadh region was four million. Calculate the incidence rate of breast.cancer in Riyadh

22. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Females constitute 49% of the population. incidence rate = 250 / 1,960,000 = 0.000128 = 0.128 per 1000 female 1.28 per 10,000 female= =12.8 per 100,000 female

23. EPIDEMIOLOGY Distribution of Disease morbidity rates Attack rate Population at risk/ period Attack rate = Number of episodes during specified period x 10 n  Acute recurrent diseases, e.g. URTI, food poisoning.  A person may catch the disease more than once.

24. EPIDEMIOLOGY Distribution of Disease morbidity rates Attack rate Example: In a village of 600 persons, 120 visits to the PHCC were due to food poisoning. What is the attack rate of food poisoning in the village ?

25. EPIDEMIOLOGY Distribution of Disease morbidity rates Attack rate Example: In a village of 600 persons, 120 visits to the PHCC were due to flu. What is the attack rate of flu in the village ? 0

26. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Factors affecting incidence: 1- New risk factor Contraceptive pills & thromboembolism. 2- Changing virulence H1N1virus & influenza pandemic 3- Changing pattern of intervention Chemoprophylaxis & meningitis

27. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Factors affecting incidence: 4-Population pattern Aging & degenerative diseases & cancer 5- Reporting Increase in reporting & Early stage of surveillance &

28. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Factors affecting incidence: 6-Screening Screening 7-New diagnostics New diagnostic early detection of cases detection of cases

29. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Factors affecting incidence: 8- Changing classification Blood pressure 140/80 mmhg Vs 160/90 mmhg incidence Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml incidence

30. EPIDEMIOLOGY Distribution of Disease morbidity rates Prevalence rate  Point prevalence  Period prevalence  It involves old and new cases  It measures the disease status in the population.  It measures the disease burden. ( All Cases)

31. EPIDEMIOLOGY Distribution of Disease morbidity rates = 1O n X Prevalence rate Point prevalence: Total cases (old + new) at fixed point of time in a place total population in that place

32. EPIDEMIOLOGY Distribution of Disease morbidity rates = 1O n X Prevalence rate Period prevalence: Total cases (old + new) during a period of time in a place total population in that place

33. EPIDEMIOLOGY Distribution of Disease morbidity rates Point prevalence:

34. EPIDEMIOLOGY Distribution of Disease morbidity rates Point prevalence: 7/18 7

35. EPIDEMIOLOGY Distribution of Disease morbidity rates From October 1, 1990 to Sep 30, 1991? Period prevalence:

36. EPIDEMIOLOGY Distribution of Disease morbidity rates From October 1, 1990 to Sep 30, 1991? Period prevalence: 1 3 4 5 6 7 9 10 10/20 2 8

37. EPIDEMIOLOGY Distribution of Disease morbidity rates prevalence rate 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.

38. EPIDEMIOLOGY Distribution of Disease morbidity rates prevalence rate Factors affecting prevalence : 1- Incidence rate Incidence rate Prevalence rate average duration of disease & 2- Disease duration = X Incidence Longer duration

39. EPIDEMIOLOGY Distribution of Disease morbidity rates prevalence rate Factors affecting prevalence : 3- management programs If successful and curative If only increases the survival without complete cure 4- Selective attrition If cases of the disease travel to be treated abroad

40. EPIDEMIOLOGY Distribution of Disease morbidity rates prevalence rate Factors affecting prevalence : 5- Changing classification Blood pressure 140/80 mmhg Vs 160/90 mmhg Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml Incidence

41. EPIDEMIOLOGY Distribution of Disease INCIDENCE VS. PREVALENCE incidence Prevalence Cure Death Migration