Uses of epidemiology Presenter : Ranjana Moderator : Dr Abhishek
Framework • History of epidemiology • Definition • Uses of epidemiology with examples
Definition of epidemiology Epidemiology is the study of the distribution and determinants of health-related events or states in population groups and the application of this study to the control of health problems (Last JM ed. Dictionary of Epidemiology, Oxford University Press, 1995)
'Epidemiology is that field of medical science which is concerned with the relationship of various factors and conditions which determine the frequencies and distributions of an infectious process, a disease, or a physiologic state in a human community' (Lilienfeld 1978).
The clinician Deals with patients Takes a history Conducts a physical Makes a diagnosis Proposes a treatment Follows up the patient The epidemiologist Deals with populations Frames the question Investigates Draws conclusions Gives recommendations Evaluates programmes Comparing the job of a clinician and the job of an epidemiologist
Uses of epidemiology • Examine causation • Study natural history • Description of the health status of population • Determine the relative importance of causes of illness, disability and death • Evaluation of interventions • Identify risk factors
1. Examine causation Genetic factors Good health Ill health Environmental factors (Biological, chemical, physical, psychological factors) Life style related factors
To study historical rise and fall of disease in the population • The diseases wax and wane (tuberculosis ) new ones appear (encephalitis, lethargica,asbestos poisoning ,LSD psychosis) old ones are eradicated (smallpox) or just fade away (chlorosis-greenish yellow discoloration of skin-female adolescent caused by IDA,miner’s nystagmus).
A Pertussis by 5-Year Age Groups B. Pertussis by <1, 4-Year, Then 5-YearAge Groups
Underground water supply Pump from river bed Place Attack rate of acute hepatitis by zone of residence, Baripada, Orissa, India, 2004 Attack rate 0 - 0.9 / 1000 1 - 9.9 / 1000 10 -19.9 / 1000 20+ / 1000 Chipat river
Common Source, interrupted exposure : • A common source, but the source introduces the infection into the vehicle only interruptedly. • Pseudomonas aeroginosa infection in urological ward • A curve will show an increase in frequency but the curve will be almost flat with occasional irregular waves coinciding with the periodic introductions of infection.
Seasonal fluctuations : • Malaria and JE are commoner during immediate post monsoon season. • Asthma shows highest incidence during spring and autumn suggesting specific environmental factors in its causation
Searching for causes and risk factors • Theories in Primitive and Middle Ages • “supernatural causes”e.g. being possessed by evil spirits, wrath of gods, punishment for evil deeds during previous births and so on). “bad air” • contagion theory • William Farr -“miasma” theory • Germ Theory -Henle-Koch postulates) • Epidemiological Wheel Theory • The Theory of “Necessary” and Sufficient” cause
Role of the host, the agent and the environment in the occurrence of disease Biologic, Chemical, Physical (injury, trauma) Social Psychological AGENT VECTOR Sanitation Weather Pollution Socio-Cultural Political Genotype Nutrition Immunity Behaviour ENVIRONMENT HOST
Syndrome identification • Epidemiologists are called “lumpers and splitters” • The differentiation of hepatitis A from hepatitis B and the distinction between several varieties of childhood leukemia. • “lumping” include the identification of many manifestations of tuberculosis. • Patterson-kelly syndrome of association between dysphagia and iron deficiency anaemia but when association was tested by epidemiological studies , it was not found.
Individual risk and chances:Life table-The ‘risks’ the average male in England and Wales
Measures of disease frequency • Prevalence • Number of cases of a disease in a defined population at specified point of time • Incidence • Number of new cases, episodes or events occurring over a defined period of time
Incidence rate Number of people who get the disease or condition in a specified time I = X Factor Total population at risk
Prevalence Number of people with the disease or condition at a specified time P = X Factor Total population at risk
Identify those sections of the population which have the greatest risk from specific causes of ill health Factors associated with anemia among pregnant women, Orissa, 2004
Community diagnosis : • The definition of indicators is a pre-requisite Indicators - to estimate the burden of illness and the strategies for control. • The main health indicators are expressed in terms of crude age-adjusted or age-specific mortality rates (such as infant mortality rates, mortality for children under 5, or maternal mortality rates), disease-specific morbidity rates, and life expectancy at birth.
3. Study natural history Death Sub-clinical disease Clinical disease Good health Recovery
4. Evaluation of interventions Treatment, Medical care Good Health Ill Health Health promotion Preventive measures Public health services
Planning • Health service administrators should not only always think of these simple routine questions, but should be alert to less obvious potential gaps in coverage. • For example, the census will state the numbers of elderly persons who live alone. Is all or only a small portion of these known to the public health nurses and others who provide home surveillance and care? • Are all needed services available, accessible, and used appropriately?
Evaluation • Evaluation is the process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to established goals.
Effectivenessrefers to the ability of a program to produce the intended or expected results in the field; effectiveness differs from efficacy, which is the ability to produce results under ideal conditions. • Efficiency refers to the ability of the program to r produce the intended results with a minimum expenditure of time and resources.
Prevalence of anemia among adolescent girls, Mandla, MP, India 2005 Description of the health status of population
Cumulated bar chart for the breakdown of many totals in proportions Estimated and projected proportion of deaths due to non-communicable diseases, India, 1990-2010 100% 90% 80% Injuries 70% 60% Communicable Proportion (%) 50% diseases 40% Non communicable 30% diseases 20% 10% 0% 1990 2000 2010 Year