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Epidemiology introduction

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  • 1. Epidemiology: An Introduction MA-SDP-III rd Semester, TU
  • 2. Epidemiology: The Subject• Greek words Epi= on or upon,• Demos=people, and• Logos=StudyRoot in the subject, that befalls on populationEpidemiology: Study of the distribution anddeterminants of health-related states or events inspecified populations, with application to the control ofhealth problems
  • 3. Scope of Epidemiology• Data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data• Described as- basic science of public health• Quantitative discipline- working knowledge of probability, statistics, and sound research methods• Method of causal reasoning based on developing and testing hypotheses• Grounded in- fields of biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events• Integral component of public health-providing foundation for directing practical and appropriate public health action based on this science and causal reasoning
  • 4. Methods in Epidemiological StudiesDescriptives: (Descriptive Epidemiology)• Frequency- number, prevalence, rate, ratios- to compare across different population groups• Pattern- occurrence of health-related events by time, place, and personDeterminants (Analytic Epidemiology)• The causes and other factors that influence the occurrence of disease and other health-related event• Searches for- “how”, “why”, “who”- understanding varying ‘risk-factors’; demographic characteristics, genetic or immunologic make- up, behaviors, environmental exposures, or otherGenerate sufficient evidences to direct prompt and effective public healthcontrol and prevention measures.
  • 5. Focus of Epidemiological Studies• Originally- Epidemics of Communicable Diseases• Since 20th century- also focused in chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health, and behavioral factors• ‘Disease’ in clinical science equals ‘Risk-factors’ in Epidemiology• ‘Patients’ in clinical science is ‘individual’, and ‘community’ in epidemiology• Clinical science “Cure” and Epidemiology ‘reduction of risks’ for all those who are exposed
  • 6. Example: Diarrheal prevalence, compare clinical and epidemiology approach Clinical EpidemiologicalTreating and caring for the individual Identifying the exposure or source that caused the illnessPatient centric Number of other persons who may have been similarly exposedConsultancy given at the individual level Potential for further spread in the community Prevent additional cases or recurrences
  • 7. A Brief historical evolution• Circa 400 B.C. - Hippocrates “On Airs, Waters, and Places,” environmental and host factors such as behaviors might influence development of disease• 1662 – John Graunt, landmark publication based on Bills on Mortality, quantify patterns of birth, death, and disease occurrence, noting disparities across population groups• 1800 – William Farr, modern vital statistics and surveillance•• 1854 -John Snow , “father of field epidemiology”, cholera outbreaks both to discover the cause of disease and to prevent its recurrence
  • 8. Spot map of deaths from cholera in Golden Square area, London, 1854
  • 9. Brief history (continued)……• 19th and 20th centuries- epidemiological methods applied in investigation of disease occurrence of communicable nature• 1930s and 1940s- non-communicable diseases were also investigated for their risk-factors, i.e., Doll and Hill- linking lung cancer to smoking• 1960s and early 1970s- health workers applied epidemiologic methods to eradicate naturally occurring smallpox worldwide• 1980s -extended to the studies of injuries and violence• Contemporary epidemiology- HIV/AIDS, SARS, MDRTB, Avian Flu, also, biologic warfares and bioterrorism• Public Health Workers- use epidemiological methods to detect and reduce day-to-day problems
  • 10. Major uses of Epidemiological Research• Assessing the community’s health – What are the actual and potential health problems in the community? – Where are they occurring? – Which populations are at increased risk? – Which problems have declined over time? – Which ones are increasing or have the potential to increase? – How do these patterns relate to the level and distribution of public health services available – Data may need to be collected and analyzed to determine whether health services are available, accessible, effective, and efficient.• Making individual decisions – Making information available on risk factors – Such as, quitting smoking, climbing stairs, eating right, using condoms while having sexual interactions, getting-married (?), every-day choices shape health in long run
  • 11. Continued….• Completing the clinical picture – Working in collaboration with clinicians and laboratorian- proper diagnosis of individual patients – However, identification of more number of similar cases and characterization of disease based on similar exposure, – SARS- China 2002 – Non-acute diseases, i.e., pulmonary, heart diseases, lung/lip/throat cancers to Cigarette Smoking• Searching for causes – Devoted to searching for causal factors that influence one’s risk of disease – Aiming to design appropriate Public Health Action – However, Eepidemiology cannot be taken as full-proof for causal relationship between an exposure and a disease – Provides, enough evidence to support effective action
  • 12. Core Functions of Epidemiology• Public health surveillance• Field investigation• Analytic studies• Evaluation• Linkages• Policy development (Recently Added)
  • 13. Public health surveillance• Ongoing, systematic collection, analysis, interpretation, and dissemination of health data to help guide public health decision making and action• To measure pulse of the community• Considered- “information for action”, pattern of disease occurrence and potential for investigation, control, and prevention measures• Contemporary Surveillance systems- injuries, chronic diseases, genetic and birth defects, occupational and potentially environmentally-related diseases, and health behaviors. Core competencies must include design of data collection instruments, data management, descriptive methods and graphing, interpretation of data, and scientific writing and presentation.
  • 14. Field investigation• Investigation of field based on reported cases from surveillance-site, – Phone calls – Fieldworks to identify, • Index-persons, unreported or unrecognized ill persons potential for further spread • Source or vehicle of infection that can be controlled or eliminated; i.e., temple holy-water, appropriate recommendations regarding isolation and quarantine
  • 15. Analytic studies• Analytic studies employing more rigorous methods are needed for identify causes, modes of transmission, and appropriate control and prevention measures• Surveillance and field investigations providing clues or hypotheses about causes and modes of transmission- descriptive epidemiology• Analytic studies evaluating the credibility of those hypotheses
  • 16. Analytic Epidemiology:• Design includes determining the appropriate research strategy and study design, writing justifications and protocols, calculating sample sizes, deciding on criteria for subject selection (e.g., developing case definitions), choosing an appropriate comparison group, and designing questionnaires• Conduct involves securing appropriate clearances and approvals, adhering to appropriate ethical principles, abstracting records, tracking down and interviewing subjects, collecting and handling specimens, and managing the data.• Analytics: Descriptive tables, computation of measures of association, tests of significance, confidence intervals and checking robustness, regression modeling etc,• interpretation – putting study findings, key take-home message, recommendations,
  • 17. Evaluation• Evaluation of public health services and other activities• Effectiveness refers to the ability of a program to produce the intended or expected results in the field• Efficiency refers to the ability of the program to produce with minimum expenditure of time and resources• Evaluation: Formative, Process, Impact (Summative) and Outcomes• Evaluation of Surveillance System: ability to detect cases or outbreaks, and its usefulness• Evaluation of public health program- Immunization: Formative, Process, Impact, Outcomes
  • 18. • Linkages : Working multi-disciplinary environment; laboratorians, sanitarians, infection control personnel, nurses or other clinical staff, and, increasingly, computer information specialists, government, academic institutions, clinical facilities, or the private sector• Policy development: working in public health provide testimony, inputs, disease control strategies, reportable disease regulations, and health-care policy