CONTENTS • Definition of EPIDEMIOLOGY TIME - PLACE - PERSON • Morbidity Rates Incidence rate Attack rate Prevalence rate • Determinants of disease • Distribution of Disease
Branches, Divisions, Components Of community health (community medicine) • Health Education • MCH • Environmental health • School health • Occupational health • Control of communicable disease • Control of noncommunicable disease
Health service administration: - Planning - Implementation - Evaluation • Demography • Community nutrition • Biostatistics • Epidemiology
الاشتقاقات Epidemiology EPI DEMOS LOGO UPON PEOPLE SCIENCE علم الناس على كاهل (دراسة) (جاثم)
What is Epidemiology? Study of distribution and determinants of health-related states and events In specified populations and application of this study to control health problems.
Distributionof Disease WHEN Time WHERE Place WHO Person
Distributionof Disease WHENTime WHEREPlace WHOPerson
Distributionof Disease WHEN Time WHEREPlace WHOPerson
Distribution of Disease • Time • Changing or stable • Cyclic • Seasonal • secular
Distribution of Disease Place • Geographic -Restricted/Wide spread -Coastal/inland • Weather(temp. , humidity , rainfall) • Altitude/latitude/longitude • Urban/rural
Distribution of Disease • Person • Age • Sex • Race • Education • Occupation • behavior
?MORBIDITY Any departure ((subjective or objective )) from state of physiological or psychological well being Distribution of disease is quantified as morbidity rates: i.e. the extent of illness, injury or disability in a defined population
Rate: a measure of the occurrence of a health event in a population group at a specified time period Number of events in time period numerator : denominator Number at risk for the event
Why are rates useful? • Can help to identifygroupswith an elevated risk of disease (High-risk Groups). • these groups can be studied to identify “riskfactors” .
RISK The probability that an event will occur. e.g. that an individual will become ill or die within a stated period of time or age. :High-risk Group A group of people in the community with a higher-than-expected likelihood Elevatedprobability)) for developing a particular disease, or a negative outcome.
Risk factor: Anaspectof personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic that is associated with an increased occurrence of disease or other health-related event or condition.
Why are rates useful? • Relatehealth events to a population base • This 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 • ------------------ INDICATORS : Measures used to predict trends , المؤشرات
Distribution of disease is quantified as morbidity rates: • Incidence rate • Attack rate • Prevalence rate
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 force of infection or disease in the community • It measures the probability that healthy people will develop disease during a specified period of time
Incidence rate • The numerator has to come from the population at risk for developing disease • The denominator may change over time as people develop disease • The denominator does not include persons with the disease However, in practice • in large studies, the denominator is often the mid-year population • in small studies, the denominator does not include persons with the disease
What is the incidence rate from October 1, 1990 to Sep 30, 1991?
What is the incidence rate from October 1, 1990 to Sep 30, 1991? 4 4/14
What is the incidence rate from October 1, 1990 to Sep 30, 1991? 4 4/18
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 rate of breast .cancer in Riyadh
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
Attack rate Number of episodes during specified period x 10n Attack rate = Population at risk/ period • Acute recurrent diseases , • e.g. URTI, food poisoning. • Person may catch the disease more than one time.
Example: In a village of 600 persons, 120visits to the PHCC were due to food poisoning. What is the attack rate of food poisoning in the village ?
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?
Factors affecting incidence 1- New risk factor Contraceptive pills & thromboembolism. Food additives & cancer New agent HIV & AIDS
2- Changing virulence El-Tor vibrio & cholera. H1N1 Influenza virus & influenza pandemic Mycobacterial resistance & TB
3- Changing pattern of intervention Eradication efforts & poliomyelitis Chemoprophylaxis & meningitis Environmental sanitation & filth diseases
4-Population pattern • Aging & degenerative diseases & cancer
5- Reporting • Increase in reporting & • Early stage of surveillance & incidence incidence
6-Screening Screening early detection of cases incidence
7-New diagnostics New diagnostic detection of cases incidence
8- Changing classification Blood pressure 140/80 mmhgVs 160/90 mmhg incidence Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml incidence
9-Selective migration Floods or famines sanitation susceptibles incidence
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.
Point prevalence: Total cases (old + new) at fixed point of time in a place x 10n = total population in that place
Period prevalence: Total cases (old + new) during a period of time in a place x 10n = totalpopulation in that place
What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991
What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991 1 2 10 3 4 7 8 5 6 9
What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991 1 2 10 3 4 7 8 5 6 10/20 9
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.
Factors affecting prevalence 1- Incidence rate & 2- Disease duration average duration of disease Prevalence rate Incidence rate X = Incidence Prevalence Longer duration Prevalence