Introduction of Epidemiology

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Introduction of Epidemiology:

Introduction of Epidemiology Dr. Nitin Solanki (M.D.) Assistant Professor Department of Community Medicine, Gujarat Adani Institute Of Medical Sciences, Bhuj 1 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

British cholera epidemics:

British cholera epidemics 1831-1832 : first modern outbreak in Britain 23,000 deaths helped to launch the sanitary reform movement 1848-1849 : 250,000 cases and 53,000 deaths prompted Snow (and others) to investigate causes 23 September 2011 2 Gujarat Adani Institute of Medical Sciences, BHUJ

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Gujarat Adani Institute of Medical Sciences, BHUJ 3 23 September 2011

John Snow’s Investigations of the Cholera Epidemics in London, 1848-1854 :

John Snow’s Investigations of the Cholera Epidemics in London, 1848-1854 23 September 2011 4 Gujarat Adani Institute of Medical Sciences, BHUJ

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23 September 2011 5 Gujarat Adani Institute of Medical Sciences, BHUJ

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The Broad Street Pump Outbreak 23 September 2011 6 Gujarat Adani Institute of Medical Sciences, BHUJ

I keep Six Honest Serving Men, they taught me all I Know , They are:

I keep Six Honest Serving Men, they taught me all I Know , They are How What Why When Where Who 7 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

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Epidemiology= Epi + Demos + Logos Epi = among Demos = people Logos = study 8 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Three Components :

Three Components Disease Frequency Disease Distribution Disease Determinants 9 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Definition of Epidemiology:

Definition of Epidemiology The study of the frequency , distribution and determinants of diseases and health - related states and events in human populations ” and the application of this knowledge in prevention , control and mitigation of these problem. ……………………by John M. Last 1988. 10 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Disease Frequency:

Disease Frequency Measurement of frequency of disease, disability or death Rates and Ratios (prevalence rate, incidence rate, death rate etc.,) Measurement of health related events and states ( Health needs, demands, activities, tasks, health care utilization) Measurements of variables 11 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Disease Distribution :

Disease Distribution Patterns of the disease distribution By time, place and person Out come – Formulation of Hypothesis Known as Descriptive Epidemiology 12 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

 Disease Determinants :

Disease Determinants To test aetiological Hypothesis To identify underlying causes (risk factors) Known as Analytical Epidemiology Helps in developing Health programmes, interventions and Policies Helps in understanding Chronic Diseases e g., Lung cancer, CVD’s 13 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Aims of Epidemiology:

Aims of Epidemiology To describe the distribution and magnitude of health and disease problems in population To identify the aetiological (risk) factors. To provide data essentials of planning, implementation and evaluation of services. 14 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Epidemiological Approach :

Epidemiological Approach Asking Questions. Making Comparisons 15 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Asking questions :

Asking questions Related to Health Events: What is the event (problem)? How did it happen ? Where did it happen ? When did it happen ? Who were affected ? Why did it happen? 16 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Making comparisons :

Making comparisons Making comparisons Between two ( or more groups) One group having the disease and the other group not having the disease Comparison between individuals 17 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Comparability:

Comparability Comparability Like can be compared with like Age and Sex or other variables Randomization or random allocation Matching Standardization 18 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Measurements in epidemiology :

Measurements in epidemiology Morbidity: Incidence, prevalence, attack rate Mortality: Crude Death Rate, Age specific death rate, Disease specific death rate, Case fatality rate Disability indicators: DALY, QuALY Natality: GRR, NRR, Age Specific Fertility rate Service indicators Operations indicators Process indicators Impact indicators Summary measures of population health 19 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Tools of measurements:

Tools of measurements Rates Ratios Proportions 20 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Ratio :

Ratio Expresses a relation in the size between two random quantities. Numerator is not a component of denominator X : Y = X/Y 21 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Proportion:

Proportion A proportion is a ratio which indicates the relation in magnitude of a part of the whole. Numerator is always included in the denominator. Give the concept of Probability. Usually expressed as percentage. 22 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Rate:

Rate Rate measures the occurrence of some particular event in a population during a given time period . So, Rate is basically proportion with an added relationship with time. 23 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Measurement Morbidity :

Measurement Morbidity “ any departure, subjective or objective, from a state of physiological well-being” Sickness, illness, disability Frequency Duration Severity 24 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Incidence:

Incidence “ the number of new cases occurring in a defined population during a specified period of time” Number of new cases of specific disease during a given time period = --------------------------------------------- X 1000 Population at risk during that period 25 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

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500 = -------- X1000 = 16.7 per 1000 per year 30,000 26 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Special incidence rates:

Special incidence rates Attack rate: type of incidence rate when population is exposed to risk for a limited period of time such as during epidemic. Secondary attack rate: the number of exposed persons developing the disease within the range of incubation period following exposure to a primary case. 27 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Uses of incidence rate:

Uses of incidence rate Useful for taking action A) to control disease B) for research into etiology and pathogenesis, distribution of diseases, efficacy of preventive & therapeutic measures 28 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Prevalence:

Prevalence All current cases (old & new) existing at a given point of time, or over a period of time in a given population Definition: the total number of all individuals who have an attribute or disease at a particular time divided by the population at risk of having the attribute or disease at this point in time or midway through the period 29 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Point prevalence:

Point prevalence Point prevalence: the number of all current (old and new) cases of a disease at one point in time in relation to a defined population. Number of all current (old &new) cases of specific disease existing at a given time period = ----------------------------------------------------- X 100 Estimated Population at the same point of time 30 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Period prevalence:

Period prevalence Period prevalence: the number of all current (old and new) cases existing during a defined period of time expressed in relation to a defined population. Number of existing cases (old &new) cases of a specified disease during a given period of time interval = ----------------------------------------------------- X 100 Estimated mid-interval Population at risk 31 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

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Case -1 Jan-1 st 2010 Dec 31 st 2010 Case -3 Case -5 Case -6 Case -8 Case -2 Case -4 Case -7 32 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

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Incidence would include cases – 3,4,5, & 8 Point prevalence ( Jan 1 st ) – 1,2, & 7 Point prevalence (Dec 31 st ) – 1,3,5 and 8 Period prevalence ( Jan – Dec ) cases 1,2,3,4,5,7 and 8 33 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

Relationship between Incidence and Prevalence :

Relationship between Incidence and Prevalence P = I X D = incidence X mean duration Incidence = P / D Duration = P / I 34 Gujarat Adani Institute of Medical Sciences, BHUJ 23 September 2011

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Gujarat Adani Institute of Medical Sciences, BHUJ 35 THANK YOU 23 September 2011

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