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DEFINITION OF EPIDEMIOLOGY

- Fundamental Science of Public Health - The study of distribution of a disease or physiologic

condition in human populations and of the factors that influence this distribution.

- Goal: o Promotion of Health o Prevention of Disease o Control of Disease

- Components: o Population o Distribution o Factors

- The study of the distribution and determinants of health-related states or events in specific populations,

and the application of this study to control of health problems.

ELEMENTS OF IDEAL EPIDEMIOLOGIC HYPOTHESIS POPULATION

- to whom hypothesis will apply CAUSE

- the particular environmental exposure - suspected risk factor

OUTCOME - the disease or condition of interest

DOSE-RESPONSE RELATIONSHIP - the amount of exposure necessary for the disease or

condition to develop TIME-RESPONSE RELATIONSHIP

- the time period between the exposure and the development of the outcome

- synonymous with: o Incubation Period for infectious disease o Latency Period for non-infectious disease

METHODS OF FORMULATING HYPOTHESIS - METHOD OF DIFFERENCE

- a DISADVANTAGE of this type of method in formulating hypothesis is the potentially large

number of hypothesis which are consistent with or are suggested by the observed difference.

- METHOD OF AGREEMENT

- COMMON FACTOR at a different circumstances that have been found to be associated with the

presence of the disease may be a CAUSE of the Disease. (HIV as an example on the book)

- METHOD OF CONCOMITANT VARIATION

- involves identifying a factor whose frequency of strength varies with frequency of disease.

- METHOD OF ANALOGY: - suggest that certain causes may be common to both disease/condition. (ex. Burkitts lymphoma)

STUDY DESIGN

a. DESCRIPTIVE STUDIES - characterize disease occurrence in a population and

is often the first step in epidemiological investigation.

b. OBSERVATIONAL STUDIES - simply observes the natural course of events.

*COHORT STUDIES - the members of the population at risk are

classified in terms of whether they had been EXPOSED or UNEXPOSED to the factor of

interest and FOLLOWED UP to determine who will develop the disease/condition being

investigated *CASE-CONTROL STUDIES

- identify the group of subjects who already HAVE the disease/condition and a comparison

group who DO NOT HAVE the disease/ condition.

c. EXPERIMENTAL STUDIES

- with various types of intervention trials.

HEALTH - the state of complete physical, mental, and social well-

being and not merely the absence of disease and infirmity.

WELLNESS - the quality that the individual enjoys as a positive good,

but only in relation to the broader realities of which he is a part.

NORMAL HEALTH - state of well being in which the individual is free from

disabling effects and has sufficient vigor to carry on the usual requirement of life, with social adaptation that

produces self-gratification and enjoyment.

HOLISTIC HEALTH - views all persons as whole beings whose individual Psycho-

Physio-Cultural-Spiritual Relationships with the environment directly affect their state of health.

PRE-PATHOGENESIS

- Phase before man is involved - the preliminary interaction of potential agent, host, and

enviroment BEFORE disease production.

PATHOGENESIS - agent become established in the host.

CLINICAL HORIZON - Stage when diagnosis can be made

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PERIOD OF INCUBATION

- the agent either multiplies, develops, or gets absorbed or fixed in the tissues.

SURVIVAL TIME - time from signs and symptoms to final outcome

CONTRIBUTING FACTORS:

I. AGENTS TYPES OF AGENTS:

A. PHYSICAL AGENTS - related to material and mechanical properties of

matter. - Ex. Light, sound, heat, cold, radiation

B. CHEMICAL AGENTS - this include exogenous substances such as carbon

monoxide from engine combustion, leads, acids, insecticides.

- also endogenous substances such as cholesterol, hormones, and others like them.

C. BIOLOGIC AGENTS - includes parasites like helminthes, protozoans,

fungi, bacteria and viruses.

CHARACTERISTICS OF AGENTS: - INFECTIVITY

- ability of the agent to gain access and adapt to the human host to the extent of finding lodgment

and multiplying within the host. - VIRULENCE

- a measure of the severity of the reaction - PATHOGENECITY

- is the measure of the ability of an agent when lodged in the body to set up a specific reaction.

II. HOST

- refers to man or group of men and is affected by the following:

1. NATURAL ACQUIRED IMMUNITY

a. NATURAL ACQUIRED ACTIVE IMMUNITY - results from previous infection where the host has

produced the antibody himself.

b. NATURAL ACQUIRED PASSIVE IMMUNITY - ex. Newborn who acquired antibody from the

mothers who have previous exposures to measles chiefly by TRANSPLACENTAL PASSAGE of maternal

antibodies into the Fetal Circulation.

2. ARTIFICIAL ACQUIRED IMMUNITY

a. ARTIFICIAL ACQUIRED ACTIVE IMMUNITY

- refers to antibodies produced by host AFTER he has received VACCINES or TOXOIDS.

b. ARTIFICIAL ACQUIRED PASSIVE IMMUNITY

- refers to the Antibodies CONFERRED to the host

through the use of GAMMA GLOBULINS (Tetanus and Rabies)

III. ENVIRONMENT - aggregate of all external conditions and influences

affecting the life and development of an organism. A. PHYSICAL ENVIRONMENT

- this includes the climate, weather, and geography of the place.

B. SOCIO-ECONOMIC ENVIRONMENT - this includes the Income of the family, Crowding in

the houses, housing facilities, availability of health facilities and others.

C. BIOLOGICAL ENVIRONMENT - this includes the vectors and animals that affect

man (Ex. Mosquitos-Malaria; Snails-Schistosomiasis)

HERD IMMUNITY - resistance of group or community

LEVELS OF PREVENTION

a. PRIMARY -HEALTH PROMOTION and SPECIFID PREOTECTION

Examples: - 4oclock Habit

- Healthy Lifestyle

b. SECONDARY - EARLY DIAGNOSIS AND PROMPT TREATMENT Examples:

- Routine BP - Blood Glucose - Peak Flow Meter

c. TERTIARY - TREATMENT and REHABILITATION

- LIMITATION of DISABILITY Examples:

- OT - Maintenance Drugs

- Desensitization

DISEASE or CONDITION DIRECTLY LEADING TO DEATH: a. Immediate Cause - Post-Op Pneumonia

b. Antecedent Cause - Mastectomy c. Underlying Cause - Cancer (Breast)

d. Other Significant Condition - Pulmonary Tuberculosis

QUALITIES OF STATISTICAL DATA a. TIMELINESS

- interval between the data of occurrence of the different events considered and the time the data is

ready to be used or disseminated b. COMPLETENESS

- has 2 components: Completeness of coverage and Completeness in accomplishing all the items in every

form.

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c. ACCURACY - refers to how the measurement or the data is to its true value.

d. PRECISION - refers to the extent to which similar information is obtained when a measurement is performed or an

observation is made more than once.

e. RELEVANCE - refers to the consistency of the data produced with

the needs of the data users.

f. ADEQUACY - collected data provide all the basic information

needed to meet the requirements of the user.

CAUSE

- something that bring about an effect or a result

CAUSAL ASSOCIATION

- an association between categories of events or characteristics in which an alternation in the frequency or

quality of one category is followed by a change in the other.

STATISTICAL ASSOCIATION - simply an association in the scientific sense.

NON-CAUSAL or SECONDARY STATISTICAL ASSOCIATIONS

- Usually results from association of both categories of events with a Third Category.

CONCEPTS IN DISEASE CAUSATION

I. BIOLOGIC ASPECTS

a. EPIDEMIOLOGIC TRIANGLE - consists of 3 components

- HOST - ENVIRONMENT

- AGENT - considers the AGENT as a SEPARATE

COMPONENT.

b. WEB OF CAUSATION - effects never depend on a single isolated cause, but rather develop as the result of

chains of causation in which each link itself is the result of a complex genealogy and

antecedents.

c. WHEEL - consists of a hub (the host or man) which

has the genetic make-up as its core. - surrounding man is the environment,

schematically divided into 3 sectors: - Biological

- Social - Physical

II. STATISTICAL ASPECTS a. Association and Causation b. Defining Variables in an Association

1. INDEPENDENT and DEPENDENT VARIABLES

2. CONFOUNDING VARIABLES - an independent variable that is a risk

factor of the disease and is associated with but not a consequence of the

exposure 3. INTERMEDIATE / INTERVENING

VARIABLES - when the effect of the exposure variable

on the disease or study condition is mediated through a third variable, the

latter is called an INTERMEDIATE. *Commonly used measures of Association

RATION MEASURES OF ASSOCIATION a. Rate Ratio b. Risk Ratio c. Odds Ratio

DIFFERENT MEASURES OF ASSOCIATION a. Rate Difference b. Risk Difference c. Attribute Fraction

III. EVIDENCE OF CAUSALITY a. Experimental Evidence not always possible b. Non-Experimental

NECESSARY CAUSE - a cause that must be present for the disease to occur

- it must always precede an effect.

SUFFICIENT CAUSE - a cause that inevitably brings a certain consequence.

RISK FACTOR

- an attribute or exposure that increases the probability of occurrence of the disease or other specific outcome.

RISK INDICATOR / RISK MARKER

- an attribute that is associated with an increased probability of occurrence of a disease or other specific

outcome and that can be used as an indicator of these increased risk. (Not necessarily a causal factor)

PATHOGENIC MECHANISM

1. DIRECT INVASION - many parasitic diseases such as:

o Amoebiasis o Giardasis

2. PRODUCTION OF TOXIN - Ex. Tetanus, Diphteria, and infection by

Enterotoxigenic Escherichia coli.

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3. IMMUNOLOGIC ENHANCEMENT OR ALLERGIC REACTION LEADING TO THE DAMAGE TO THE HOST - Ex. Tuberculosis, post-streptococcal

glumerulonephritis, dengue hemorrhagic fever

4. PERSISTENT OR LATENT INFECTION - Ex. Reyes Syndrome, Varicella, Influenza B virus

5. ENHANCEMENT OF HOSTS SUSCEPTIBILITY TO DRUGS OF OTHERWISE MINIMAL TOXICITY

6. IMMUNE SUPPRESSION

COLONIZATION - agent propagate at a rate sufficient to maintain its

numbers without producing identifiable evidence of any reaction in the host.

INAPPARENT INFECTION

- also known as Sub-clinical Infection - the organisms not only multiply in the host, but also cause

a measurable reaction that is not clinically detectable.

INFECTIOUS DISEASE - infection leads to clinical disease with symptoms, physical

findings , or both.

TYPES OF CARRIER

Type of Carrier

Example

Inapparent Throughout Polio virus, Meningococcus, Hepatitis Virus

Incubatory Carrier Viruses of chickenpos, measles, and hepatitis

Convalescent Carrier C. Diptheria, Hepatitis B Virus, and Salmonella Species

Chronic Carrier S. Typhosa, Hepatitis B Virus SECONDARY ATTACK RATE

- measures the spread of disease within a group - defined as the number of cases of a disease developing

during a stated time period among those members of a closed group who are at risk.

EPIDEMIOLOGY OF NON-COMMUNICABLE DISEASES

I. ENVIRONMENTAL EPIDEMEOLOGY - the study of environmental factors that influence the

distribution and determinants of disease in human populations

II. OCCUPATIONAL EPIDEMIOLOGY

- the study of the workplace exposures on the frequency and distribution of diseases and injuries in the

population.

ENVIRONMENTAL FACTORS THAT MAY AFFECT HEALTH: 1. Physiological Factors

- Stress, Shift Work, Human relationship

2. Biological Factors

- Bacteria, Viruses, Parasites 3. Accident Factors

- Hazards, situation speed influence of alcohol, drugs 4. Physical Factors

- Noise, Climate, Workload, Lighting radiation, Economics

5. Chemical Factors - Chemicals, Dust, Drugs, Tobacco, Skin irritants, Food

Additive

INFECTIOUS vs. NON-INFECTIOUS DISEASES INFECTIOUS DISEASE NON-INFECTIOUS DISEASES

Single necessary agent No single necessary agent Specific agent-disease relationship

One-to-one correspondence between agent and disease very rare

Causes are relatively well understood

Causes unknown, intervention usually based on risk factors

Short Incubation Period Long Latency Period Single Exposure usually sufficient May require multiple exposure to

same or multiple agents Usually produce acute disease Most often produce chronic

disease Acquired Immunity possible Acquired immunity unlikely Diagnosis based on tests specific to disease agent

Diagnosis often dependent on non-specific symptoms or tests.

COMMON SOURCE EPIDEMICS

- these are outbreaks caused by exposure of a group of persons to a common noxious influence.

PROPAGATED or PROGRESSIVE EPIDEMICS

- result from transmission, either direct or indirect, of an infectious agent from one susceptible host to another.

VECTOR-BORNE EPIDEMIC

- result of vector-borne disease. - usually has a small geographic area as a common source

but may have a zoonotic, human or mixed cycle as the source of the pathogen to the vector.

INVESTIGATION OF EPIDEMICS (Refer to Page 70 of FCM handouts)

*Define a case: verify the diagnosis *Data analysis: report the investigation *etong dalawa lng tinanong eh..

ENDEMIC -the constant presence of a disease or infectious agent

within a given geographic area. EPIDEMIC

- the occurrence in a community or region of cases off an illness (or an outbreak) with a frequency clearly in excess of

normal expectancy STERILIZATION

- the elimination of microbiological organisms to achieve asepsis, a sterile microbial environment

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FUMIGATION

- a technology that provides a specific dose of ionizing radiation from a source such as radioisotope.

INCIDENCE RATE

- the number of new cases of a specified disease diagnosed or reported during defined period of time, divided by the

number of persons in a stated population the in which the cases occurred.

ATTACK RATE - the cumulative incidence of infection in a group of people

observed over a period of time during an epidemic.

INFESTATION

- for persons or animals, the lodgment, development and reproduction of arthropods on the surface of the body or in

the clothing.

STRICT ISOLATION - this category is designed to prevent transmission of highly

contagious or virulent infections that may be spread by both air and contact.

- Private Room + Masks + Gowns + Gloves

AFB ISOLATION - aka Tuberculosis Isolation

- for patients with pulmonary TB who have a positive sputum smear or a chest x-ray that strongly suggests active

TB. - Private Room + Special Ventilation + Closed Door +

Respiratory-type Mask

ABSOLUTE or COMPLETE QUARANTINE - the limitation of freedom of movement of those exposed

to a communicable disease for a period of time not longer than the longest usual incubation period of that disease.

METHOD QUARANTINE

- a selective or partial limitation of freedom of movement of contacts, commonly on the basis of known or presumed

differences in susceptibility and related to the danger of disease transmission.

1. Sensitivity 2. Specificity 3. Sensitivity: 90% 4. Specificity: 90% 5. Positive predictive value: 8.3% 6. Negative predictive value: 99.9% 7. Feb-march 2010 epidemic in the phils: dengue? 8. Epidemiologic surveillance? 9. Cases: 3+4+4

*I HAVE NO IDEA.. Decode nyo nlng )