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Sunday, September 03, 2006

Epidemiology Notes - Quick Study Review

EPI=UPON DEMO=POPULACE OLOGY=THE PROCESS OF STUDY

EPIDEMIOLOGY= A SCIENTIFIC METHODOLOGY USED TO DETECT THE CAUSE OR SOURCE OF DISEASES, DISORDERS, SYNDROMES, CONDITIONS, ETC. WHICH RESULT IN DISABILITY OR DEATH IN A POPULATION.

THREE GENERAL PURPOSES OF EPIDEMIOLOGY
1. EXPLAIN THE ETIOLOGY (STUDY THE CUASE OF DISEASE)
2. DETERMINE IF EPIDEMIOLOGIC DATA ARE CONSISTENT WITH PROPOSED HYPOTHESIS AND CURRENT MEDICAL KNOWLEDGE.
3. PROVIDE A BASIS FOR DEVELOPING CONTROL MEASURES AND PREVENTION PROCEDURES FOR GROUPS AT RISK
Develop PREVENTION AND TREATMENT PRACTICES,
MEASURING THE SUCCESS OF INTERVENTION STRATEGIES.

OR ANOTHER WAY TO PUT IT…
1. TO PREVENT/PREDICE
2. TO TARGET
3. TO JUSTIFY
The main purpose of all these is to eradicate in order to
ü Save money
ü Altruism
ü Describe the clinical picture
ü Syndromes
ü Diagnosis
ü Risk behavior
ü Other factors
ü Demonstrate most effective measures/treatment


Traditional Epidemiology
The epidemiological triangle:

Agent=cause of disease
Host=carrier or suscept ind.
Environment=where you find the host and agent
(time is in the middle)
Epidemiology is attempting to break the relationship between any of these factors.
Most commonly used for infectious disease.

Web of causation:

(looks like dr. chens notes)
Multiple causes each interrelated to explain the “cause”. More complex than the epi tri.
Persons in biostats would assign a relative importance and give a weighted mean.


Other general:
The wheel: not common.
Each disease has a genetic core surrounded by physical, biological. And social env. Depending on the situation, each factor may be smaller or larger

The gordon model:
Agent versus host with the fulcrum of the environment in the center.

See handout: The natural history of disease process. Used child abuse example.


4 categories of agents:
1. Biological (protozoa, bacteria, virus, etc)
2. Physical (noise, light, heath, radiation, cold, vibration)
3. Chemical (lead, abestos, food additives, smoke
4. Nutritional (lack of (usually), or imbalance).

Characteristics of agents:
Infective=ability to infect host
Pathogenic=capacity to cause disease
Virulence= degree of pathogenicity
Invasive=ability to enter body and spread
Antigenicity=ability of agent to stimulate production of antibodies
Toxicity=degree to which cause harm to host.

Factors that influence spread of disease:
Age (most important)
Gender (disease specific)
Race (sickle cell)
Religion (diet)
Customs (female circumcision)
Occupation (exposure to noise, lead, stress)
Heredity
Marital status (women primary physician interfact…married men more likely to go)
Family background
Previous disease (more or less suscept)










Environmental factors that influence disease causation or progression
Temperature
Humidity
Altitude
Crowding
Housing
Neigborhood
Water supply
Milk and food
Radiation
Air and noise pollution


Chain of infection:
1. Etiologic agent (that which causes the diease
2. Reservoir (animate or inanimate)
Clinical (acute) or Carrier
Carrier: Active (individual exposed to and harboring disease organism for an extended time after recovering)
Convalescent (exposed to and harboring pathogen in the recovery phase but still infectious.
Healthy and Passive (exposed to and harboring pathogen without becoming ill.
Incubatory (exposed to and harboring pathogen in the beginning stages.
Intermittent (exposed to and harboring pathogen who can intermittently spread the disease.
3. Portal of exit (skin, transplacental, respiratory, gentourinary, ailementary etc)
4. Mode of transmission (direct versus indirect)
5. Portal of entry (generally same as exits)
6. Susceptible host (degrees of suscep dependent upon immunity of host).

Hyperendemic=persistent level of activity beyond the expected prevalence associated with small poulations.
Holoendemic=disese that is highly prevalent in a population and commonly acquired early in life (chickenpox)
Epidemic=outbreak of one specific disease form a single source in a give population or area in excessof the usual level of expectancy. The seriousness and severity influence the definition of an epidemic. New cases exceed the prevalence of a disease.
Pandemic=and epidemic that is worldwide.





Measures of sickness:
Incidence=The number of new cases or a specific period of time.

Prevalence=the number of people in a pop. With the disease/cond. At a given point in time. There must be incidence to be prevalence.

Point prevalence: total number of cases at a specific moment in time

Period prevalence: Total number of cases in a prescribed period of time…from/to
When assessing period prevalence, a recurring case is treated as a new case.

Rate=the amt or number of one thing measured in units of another

Morbidity= the frequency of illness or disability in a pop.

Attack rate=an incidence rate expressed in percentage form.

Measures of death: Mortality

CDR=crude death rate: the actual number of deaths in a given time

Cause specific mortality rate=total number of death for a given disease in a given year.

Case fatality rate= the number death by a certain cause in a given time over the number of diagnosed cases.

Infant mortality rate= the number of children death less than one year old over the number of live births.

Infant death rate=the number of child deaths less than one year over the total pop.

Neonatal mortality rate=the number of infant deaths less than 29 days old over the number of live births in one year.

Post neonatal mortality rate=the number of infant death s from 28 days to one year over the number of live births in the same year.

Fetal death rate: the number of stillborn in one year over the total number of births in one year x 1000.

Fertility rate=probability rate of birth

Rate formula= numerator: number of cases of a disease over the denom. Which is the population in a given period of time. Then multiplied by a given value (say K) relevant to the population under study.

A rate in epi is the frequency/number of disease per unit size of population

Adjusted rates=used to allow for a fair comparison between groups which differ in some important characteristics (say age or gender). Adjust for a skewed rate.

Ratio=the raltion of a number, degree, event, etc between 2 similar things. Generally mutually exclusive to compare one to another. Try to always use 1:….

Ratio formula: dividing one quantity by another as expressed by a fraction.

Proportions= percentages. The relationship between the amount, size, and degree of one thing to another.

Proportion formula: divide the numerator by the denominator and mult by 100 to get a percentage.

Sensitivity and specificity: ensure reliability.

Sensitivity: Correctly id those who have the disease.

Specificity: Correctly id those who do not have the disease.

Sources for Epi info:

Mortality stats
Mobidity stats
Lab. Reports
Case study investigations
Vector studies
Special surveys


Definitions:

Fomites: inanimate objects that serve in disease transmission.

Vector: non-human living carrier of disease

Reservois: any organic thing in which organism live and multiply.
Zoonoses: animal transmission to human

Case: a person diagnosed with the disease

Primary case: the fist case introduced into the population

Index case: the first case brought to the attention of the epidemiologist

New case: first occurrence or a new case of the same disease

Suspect case: not yet diagnosed.

Case fatality ratio: the number of deaths due to specific disease per 100 episodes of dis.

Case severity: determined by several variables including avg length of stay in hosp, how disabling, chances of recovery, etc.


Levels of prevention:
Primary: halting disease or disorder before it happens.
Secondary: discovering pathogenic states/conditions in a population.
Tertiary: block the progression of a condition.

Pathogens:organisms capable of causing disease
Pathogenesis: the process of generating disease
Pathogenicity: ability of a pathogenic substance to cause disease.

Infective: those where the pathogen can enter, survive, and multiply in the host.

Virulence: the strength of different organism or degree of pathogenicity.

Invasiveness: the capacity to enter and grow on tissues of the host.

Etiology: cause of disease.

Three levels of disease:
Acute
Subacute
Chronic

Five classifications of disease
Congenital and heredity
Allergies and inflammatory
Degenerative or chronic
Metabolic
Cancer/neoplastic

Communicability: ability to be spread.

Classification by cause:
Airborne/Respiratory
Intestinal discharge
Open sores/lesions
Zoonosis or vector born
Fomite born

Classification by microbe source:
Bacteria
Virus
Fungus/mold/yeast
Protozoan
Worms
Arthropods

Classification by formite:
Dusts
Funes
Smoke
Chemicals
Electric
Noise
Radiation
Thermal
Bites,
Stings


Herd immunity: if most of the people in a population are protected, the chances or an epidemic are minimized. (immunizations)

Three factors to controlling communicable disease:
Remove, eliminate or contain the cause or source
Disrupt and block the chain of transmission
Protect susceptible populations.

Environmental controls:
Providing clean water, sewage, nutrition, animals and public utilities, etc.

Host related controls:
Quarantines
Isolation
Sanitaion
Hygiene
Immuniztions
Chemoprophylaxis

4 levels of quarantine:
segregation
surveillance
modified quarantine
complete quarantine


People to know:

Hippocrates: recognized airborne disease, atomic particles, etc.

Syndenham: (1600’s) advocated hygiene principles and began classifying disease states.

Lind: (1700’s) Scurvey epidemic in sailers. By identifying nutritional effects on disease he also observed the sources of causation, place, time, and season.

Jesty: (1774) Smallpox.
Jenner: (1700’s) Smallpox. More widely known.

Semmelweis: (1800’s) Childbed fever.

Snow: (1800’s) Cholera epidemic

Pasteur: (1800’s) vaccine

Koch: (1800) Methodology. Showed world first picture of microorganism. Pioneered the identification of microorganisms….

Leuwenhooek and Drebel: Microscope

Graunt: Drew up bill or mortality and other vital statistics.

Ramazzini: Italian guy who was interested why certain workers went blind. Advent of occupational health and industrial hygiene epidemiology.

Typhoid Mary: Early 1900’s cook responsible for large outbreak of typhoid. Illustrated the need to track carriers and control food supplies etc..

Note: nutrition one aspect of early epidemiology as deficiencies were correlated with disease such as ricketts, night blindness, etc.


Two types of epidemics:

Common source epidemic: where everyone gets it from the same place such as food poisoning at a picnic from bad potatoe salad.

Propagated or progressive source epidemic: where an outbreak occurs and then is spread from person to person, fomite, vectors, etc. Cannot chart a clean curve.

Vital statistics include all major life events combined with health and other status information such as on the census.
Vital events registrations include births, marriage, divorce, death.

Sources for vital stats include:

National vital stats center
National survey of family growth
National health interview survey
National health and nutrition exam survey
Natinal master facility inventory
National hospital discharge survey
National nursing home survey
AIDS surveillance
National notifiable diseses surveillance system.
Abortion surveillance x 2 sources
US immunization survey
National occupational exposure survey
National survey on drinking and drug abuse
Mental health organizations.
Medicaid/Medicare
Census
National health expenditures
Surveillance, epidemiology and end results program
Consumeer price index
Employment and earnings
Environmental protection agency
World health org.



Types and osurces of data for descriptive stats

Nominal: classify using categories that lack numbers such as age, gender, race. Parametric

Ordinal: Heiarchial classification of categories such as a ligert scale 1-5.
Parametric

Interval: No zero point. Tells absolute value between categories or units of measurment
Nonparametric

Ration: Has a zero point and tells value between categories.
Nonparametric

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