1. Introduction to Epidemiology

2. Definition Epidemiology: Epi (upon) + demos (people) + logy (study of)
The study of the distribution of a disease or
condition in a population and the factors that
influence that distribution.
Epidemiology is a discipline that describes, quantifies, and postulates causal mechanisms for health phenomena in populations.
Epidemiology is concerned with the distribution and determinants of health and diseases, morbidity, injuries, disability and mortality in populations.
The Study of the distribution and determinants of health - related states or event in specific populations, and the application of this study to the control of health problems
Determinants: ANY FACTOR, EVENT CHARACTERISTIC OR ANY OTHER DEFINABLE THING THAT BRINGS CHANGE IN A HEALTH CONDITION:
BACTERIAS,
CHEMICAL AGENTS
STRESS
ADVERSE LIFESTYLE
DIET HIGH IN SATURATED FAT

3. Basic Research Terminology
Retrospective: Refers to time of data collection
Case Control Study: Persons w/ disease & those w/out are compared
Cohort Study: Persons w/ and/or w/out disease are followed over time

4. Aims & Levels As the basic method of public health,
epidemiology is concerned with efforts to:
Describe the health status of the population
Explain the etiology of disease
Predict the occurrence of disease
Control the distribution of disease
ENUMARATE CASES OF d, OBTAIN Frecuencies of the D w/n subgroups, trends in the occurrence of the disease
Discover causes of the disease and modes of transmission
Estimates # of cases & identify distribution w/n Population this is important for the planning, intervention and allocation of resources
Prevent occurrence of new cases, eradicating existing cases, and to prolong the lives of those with the disease

5. Terminology (Cont.)
Cross-sectional Study: Presence or absence of exposure to possible risk factor measured at one point in time. Prevalence obtained.
Prevalence: The # of new cases and existing cases during specified time period.
Incidence: The # of NEW cases per unit of a population at risk for disease occurring during stated time period.

6. Foundations Human diseases do not occur by chance
Factors that cause or contribute to diseases and injuries can be identified by means of systematic investigation

7. Goals
Improve the understanding of the natural history of disease and the factors that influence its distribution
Intervention

8. Historical Antecedents
Hippocrates: Environment – disease causation
Graunt: Vital statistics in the mid 1600
Snow: Natural experiments to track cholera outbreak in London
Koch: Human disease - micro-organism / a disease
1 Epidemiology began with the Greeks 400 BC
Ancient epidemic disease: environment
Disease associated with the physical environment ….moved away from the supernatural explanations
Bio –Statistics pioneer, compiled
4. His postulates advanced the theory of specific disease agent

9. Epidemiologic Approach
Quantification
Use of special vocabulary
Interdisciplinary composition
Quantification: enables the E to investigate the source of variation of a disease by Tiempo, Place and person
It is the translation of qualitative impressions into numbers

10. Epidemiologic Approach: Special Vocabulary
Epidemic – Pandemic – Endemic
Epidemic: Excessive occurrence of a disease.
Epidemicity: Relative to usual frequency of the disease in the same area, among the specified population, at the same season of the year.
OCURRANCE OF more cases of disease than expected in a given area or among a specific group of people over a particular period of time

11. Pandemic: Epidemic on a worldwide scale
Endemic: Characterize a disease that is habitatually present in a particular geographical region. (Malaria and Cholera)
Surveillance: Systematic collection, analysis, interpretation, dissemination of data.
PANDEMIC Epidemic occurring in several countries or continents, afecting a large proportion of the po
ENDEMIC Constant present of a disease or infectious agent within a given geographical area or population group

12. Descriptive Variables for the Health of the Community
Demographic & Social Variables
Age and Sex
Socioeconomic Status
Family structure
Racial, ethnic and religious composition
Variables related to community infrastructure
Availability of social and health services
Quality of housing stock
Social stability
Family Structure includes marital status and number of single parent family
Social Stability – residencial mobility

13. Health Related Variables
Homicide and suicide rates
Infant Mortality Rate
Mortality from Specific Condition
Magnitude of chronic and infectious diseases
Alcoholism and drug abuse rates
Teenage pregnancy rates
Birth Rate

14. Population Dynamics and Epidemiology
Three factors affect the size of populations:
Birth
Death
Migration
When is the Po in equilibrium?,
What is a fixed Po?,
What is a dynamic Po?,
When a Po is in steady state?
When B, D and M do not contribute to either increase or decrease the number of persons
A fixed Po adds no new members, so decreases in size as a result of death only
Adds new members through B and M and looses members through D and Emigration
When the # of members exiting equals the # of members entering

15. Epidemiologic Triad: Traditional Model of Infectious Disease Causation
The epidemiologic triangle recognized three factors in the pathogenesis of disease:
Host
Susceptible host
External agent
The E brings the H and A together
Agent
Environment

16. The Agent
Agent: must be present for an infection to occur: Microbial agents
Characteristics of Infectious disease agents:
Infectivity
Pathogenicity
Virulance
Toxigenicity
Resistance
Antigenicity
Microbial Agents include: bacteria, viruses, fungis, intestinal parasites, insect vectors that carry a disease agent from its reservoir to humans
Infectivity: Capacity of the A to enter and X in a susceptible host and produce infection or disease
Pathogeneticity: Capacity of the A to cause disease in a infected host
Virulence: refers to the severity of the disease
Toxigenicity: refers to the K of the agent to produce a toxin or poison
Resistance: refers to the ability of the agent to survive adverse environmental conditions
Antigenicity: refers to the ability of the agent to produce antibodies in the host
RESERVOIR habitat where As lives (humans, animals, environmental)
AGENT: A factor such as a micro organism, chemical substance, from of radiation…whose presence, excessive presence or relative absent is essential for the ocurrance of a disease

17. Agent Host
After exposure: from sub-clinical infection (inapparent) to active case of the disease.
End Result: Recovery, disability, disfigurement, death.
Ability to fight infections, comprises 2 broad categories:
Non-specific defense mechanisms
Disease specific defense mechanisms
HOST: person or living organism that can be infected by an infectious agent
saliva, skin, tears
immunizations

18. The Environment
Domain in which the disease-causing agent may exist, survive or originate.
Acts as a reservoir or niche that fosters the survival of infectious disease agents. The reservoir may be a part of the physical environment or may reside in animals or insects (vectors) or other human beings (human reservoir – host)
External Environment: physical, biologic, social, economic components
Human: case or carrier
Case – person identified w/ disease
Carrier – asymptomatic, lack of infection
Physical: weather, temperature, humidity, geological foundation
Social: behavior, personality, culture
Enhance or diminish survival of disease agents and may serve to bring agent and host into contact

19. Means of Transmission – Directly or Indirectly from reservoir
Direct Transmission: Spread of infection through person to person contact
Portals of exit: sites where infectious agents may leave the body (respiratory passages, the alimentary canal, the openings in the genitourinary system, and skin lesions. Also through insect bites, the drawing of blood, surgical procedures and accidents)
Portal of entry: respiratory system (influenza, cold), the mouth & digestive system (hepatits A), mucous membranes or wounds in the skin.

20. Indirect Transmission: through an intermediary source
Vehicle: contaminated H2O, infected blood on used hypodermic needles.
Fomites: inanimated objects: doorknob or clothing.
Vectors: animate, living insect or animal that is involved with transmission of the disease agent.
Vehicle: an inanimated intermediary in the indirect transmission of an agent that carriers the A from a reservoir to a susceptible H
Vector: an animate intermediary
Human: case (person infected with the D) / carrier (asymptomatic, lack of infection)

21. Some Measures Used in Epidemiology
Counts: Number of individuals with a certain disease/exposure
Proportions: (P)
One’s status in relation to group
Ratio: A fraction in which there is not necessarily any specified relationship between the numerator & denominator.
Rate: A ratio in which time forms part of the denominator
Prevalence: # of existing cases of a disease / health condition in a Po at some designated time (specified or not).
Proportions: 10 UC ss with Hepatitis
How large of a problem this is: 20 Ss (50%) vs 500 Ss (2%)

22. Infant Mortality Rate: (IMR) risk of dying during the first year of life among infants born alive (aged days)
Perinatal MR: measures risk of dying among late fetal death + infant deaths within the 7 days of birth. (28 weeks gestation to 7 days of life)
Noenatal MR: measures risk of dying among infants younger than 28 days
Postneonatal MR: measures risk of dying among older infants (28 days to 12 months)

23. Incidence Rate: (IR) rate of development of new cases
Crude Mortality Rate: (CMR)
# of annual death Po
Maternal Mortality Rate: MMR number of maternal death ascribed to childbirth
Age-Specific Mortality Rate: ASMR
# deaths in specific group per total number of people in that age group
Proportional Mortality Rate: PMR # of death within a Po due to a specific disease

24. Specialized Epidemiological Measures
Years of Potential Life Lost (YPLL)
Measures # of years lost due to a cause
It is based on projected life expectancy
Dependency Ratio (DR)
Proportion of dependents in a society to the number of adults (19-63)
DR= # under 18 and over 64
# between 18 and 65