By: Dr. Khalid El Tohami

Objectives  At the end of the session the student should be able to:  Define epidemiology, what are the basic measurements in epidemiology  Explain the uses of epidemiology  Describe epidemiology of infectious diseases.  Describe screening of diseases.

Epidemiology  Epi= among; demos= people; logos= study  It is the basic science in preventive and social medicine.  Covers health and health related diseases.  Provides new opportunities for prevention, treatment, planning and improving health services.

Definitions  They are many:  Last definition: “The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems”

Components of Epidemiology 1. Disease frequency  Rates, ratios and proportions. (comparisons lead to clue to aetiology) 2. Distribution of disease  By time, place and persons. (descriptive epidemiology, generating hypotheses) 3. Determinants of disease (analytical epidemiology, testing aetiological hypotheses)

Aims of Epidemiology  To describe distribution and magnitude of health problems.  To identify aetiological (risk) factors.  To provide data for planning. “the ultimate aim is to lead effective action: (a) to eliminate or reduce the health problems and (b) to promote health.

Epidemiology and Clinical medicine EpidemiologyClinical medicine Unit of study is defined populationUnit of study is a case The concern is in the disease pattern in the population The concern is in the disease in the patient The investigator goes out to the community The patient comes to the doctor Using tables and graphs to diagnose Using clinical picture and laboratories Seeks aetiology to recommend control and prevention Seeks a diagnosis to give treatment to patients

Epidemiological Approach  It based on 2 major foundations: 1. Asking questions. (what, where, when, why, who, how) 2. Making comparisons. (between groups, comparability)

Basic Measurements in Epidemiology a) Measurements of mortality. b) Measurements of morbidity. c) Measurements of disability. d) Measurements of medical needs. e) etc…….

Tools of Measurements 1. Rates 2. Ratios 3. Proportions

Measurements of Mortality  Mortality rates and ratios: Crude death rate. Specific death rates. ○ Disease specific death rate ○ Age specific death rate ○ Sex specific death rate ○ Income specific death rate Proportional mortality rate. Standardized rates.

Measurements of Morbidity  Incidence  Prevalence

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7 Case 8 Jan 1Dec 31 Incidence cases= Point prevalence Jan 1 cases= Point prevalence Dec 31 cases= Period prevalence Jan-Dec cases=

Epidemiology of Infectious Diseases.  Infection: “The entry and development or multiplication of an infectious agent in the body of man or animal”  Contamination: “The presence of an infectious agent on a body surface, on or in cloths, toys, surgical instruments, dressing or substances including water, milk and food”

 Infestation: “It is the lodgment, development and reproduction of arthropods on the body or cloths”  Host: “A person or animal that afford lodgment to an infectious agent under natural conditions”

Define the Following: Infectious diseaseContagious disease Communicable diseaseEpidemic EndemicSporadic Pandemicexotic ZoonosisEpizootic EpornithicNosocomial infection Opportunistic infectionIatrogenic disease Surveillanceeradication

Dynamics of Disease Transmission Susceptible Host Modes Of Transmission Source or Reservoir

Screening of Disease  Concept of screening The active search for disease among apparently healthy people and it is a fundamental aspect of prevention.  Definition “The search for unrecognized disease or defect by means of rapidly applied tests, examinations or other procedures in apparently healthy individuals”  Screening is capable of wide application, relatively inexpensive and require little physician-time