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PATH216

g. INTRODUTION to GENERAL EPIDEMIOLOGY. PATH216. Mohamed M. B. Alnoor. EPIDEMIOLOGY. CONTENTS. Definition of EPIDEMIOLOGY Other Definitions TIME - PLACE - PERSON M orbidity Rates Incidence rate Attack rate

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PATH216

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  1. g INTRODUTION to GENERAL EPIDEMIOLOGY PATH216 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

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

  4. EPIDEMIOLOGY What is Epidemiology? distribution and determinants

  5. EPIDEMIOLOGY What is Epidemiology? Distributionof 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: MORBIDITY : Any departure ((subjective or objective )) from state of well being (physiological or psychological) i.e. the extent of illness, injury or disability in a defined population

  10. EPIDEMIOLOGY Distribution of Disease Distribution of disease is quantified as morbidity rates: Rate: a measure of the occurrence of a health event in a population group at a specified time period occurrence population group time period Number of events in time period numerator : denominator 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 identifyHigh-risk Groups (groups with an elevated risk of disease). these groups can be studied to identify “riskfactors” • 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 X = 1On Incidence rate Population at risk/ year/locality • It involves only the new cases. • It measures the probability that healthy people • will develop disease during a specified period of time

  17. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate • The numerator is newcases • 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

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

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

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

  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 Number of episodes during specified period x 10n Attack rate = Population at risk/ period • 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. 0 What is the attack rate of flu in the village ?

  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 incidence Increase in reporting & Early stage of surveillance & incidence

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

  29. EPIDEMIOLOGY Distribution of Disease morbidity rates Incidence rate Factors affecting incidence: 8- Changing classification Blood pressure 140/80 mmhgVs 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 Prevalence rate Point prevalence: Total cases (old + new) at fixed point of time in a place X = 1On total population in that place

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

  33. EPIDEMIOLOGY Distribution of Disease morbidity rates Point prevalence: What is the point prevalence on April 1, 1991?

  34. EPIDEMIOLOGY Distribution of Disease morbidity rates Point prevalence: What is the point prevalence on April 1, 1991? 7 7/18

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

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

  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 & 2- Disease duration average duration of disease Prevalence rate Incidence rate X = Incidence Prevalence Prevalence Longer duration

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

  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 prevalence Incidence prevalence Incidence

  41. EPIDEMIOLOGY Distribution of Disease incidence Prevalence Incidence Vs. prevalence Cure Death Migration

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