2. Epidemiology: The Subject
• Greek words Epi= on or upon,
• Demos=people, and
• Logos=Study
Root in the subject, that befalls on population
Epidemiology: Study of the distribution and
determinants of health-related states or events in
specified populations, with application to the control of
health 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 Studies
Descriptives: (Descriptive Epidemiology)
• Frequency- number, prevalence, rate, ratios- to compare across different
population groups
• Pattern- occurrence of health-related events by time, place, and person
Determinants (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 other
Generate sufficient evidences to direct prompt and effective public health
control 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 Epidemiological
Treating and caring for the individual Identifying the exposure or source that
caused the illness
Patient centric Number of other persons who may have
been similarly exposed
Consultancy 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
