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40 Cards in this Set
 Front
 Back
Epidemiology

Study of distribution and determinants of health and disease in POPULATIONS


Primary prevention

prevent disease from occuring


Secondary prevention

early detection to change natural history


Tertiary prevention

reducing disability after treatment


Determinants of distribution

Infectious agents
Carcinogens, chemicals Behaviors, habits, lifestyle Occupational exposures aging genetic constitution social/political factors 

Epidemiologic triad includes?????

Host
Environment Agent 

Distribution:

Who
Where When How Changes 

Epidemic?

Higher than normal levels of disease


John Snow used what approach to epidemiology?

Ecologic and observation or retrospective cohort design


Koch's postulates

1. agent recovered from all diseased individuals
2. Agent grows in culture 3. Cultured organism causes new disease in susceptible 4. Agent recovered from new diseased animal 

Revised causal criteria for disease

1.Temporal relationship
2.Strength of association (relative rate) 3. Biologic plausibility 4. Risk factor 5. Consistency: association is replicated by other investigators 6. Dose response 

Herd immunity

1. Resistance to the spread of infectious disease in a group because susceptible members are few, making transmission from an infected member unlikely.
2. The immunologic status of a population, determined by the ratio of resistant to susceptible members and their distribution. 

Outbreak investigation

1. define numerator (cases)
a. case definition 2. define denominator: population at risk 3. Calculate attack rate (incidence rate of people at risk) 

Attack rate:

# at risk with disease/total # at risk
(%) 

Secondary attack rate:

# contacts who develope disease/
#total susceptible contacts this also is a measure of tendency of spread in a population 

Attack rate ratio:

Attack rate % for sick students who ate fish /Attack rate % for sick students who did not eat fish.
A good rule of thumb for determining a relationship for attack rate ratios (or risk ratios) in foodborne disease: >5 Very strong association (increased risk) 3.0 <5.0 Strong association (increased risk) 1.7 <3.0 Moderate association (increased risk) 1.31.6 Weak association (increased risk) 0.91.2 Probably no association 0.50.8 Weak association (decreased risk) 

Incubation Period

Interval from recipt of infection to the time of onset of clinical illness


susceptibile

the probability to get disease (NEVER 0)


nonsusceptible

the probabilty to get disease IS ZERO


Steps to epidemiology study

1. Define disease
2. Define population 3. Find all cases in the population (existing and new) 4. Create measures of case frequency per population 

Prevalence (A SNAPSHOT)

# the total number of cases of a given disease in a specified population at a specified time and/or
# the ratio of the number of cases of a disease present in a statistical population at a specified time and the number of individuals in the population at that specified time. NOT a measure of risk and NOT a rate 

Point prevalence

How many on a certain date? aka crosssectional sample


Period prevalence

disease cases present during a specific time interval (NOT a good measure)


prevalence case bias

bias due to longer disease survivability


RATES

proportions, ratios, risk and instataneous rates over TIME


Proportion

includes the numerator in the denominator


ratio

numerator and denominator come from different groups (male/female)


Risk

result of rates that prevail over a period of time. Time is not a dimension; only used descriptively to specify a period of observation


Cumulative incidence CI:

number of new cases divided by the candidate population over a period of time.
also be calculated by the incidence rate multiplied by duration. CI(t)=1e^{IR(t) * D} new cases/initial population at risk 

Incidence Rate IR (density)

new cases/at risk time
"stroke incidence for males is 5 cases/100,000 personyears 

Incidence Density ID

new cases/personyears


Crude rates

total number of something per 1000 people. summary for a population of comparison age group. Not used for interpopulation comparisons.


standardised mortality rate (SMR) or agespecific mortality rate (ASMR)

total number of deaths per 1000 people of a given age (e.g. 1665 or 65+).
Factors affecting a country's death rate * Nutrition levels * Standards of diet and housing * Access to clean drinking water * Hygiene levels * Levels of infectious diseases 

Specific Rates

ALWAYS can be compared between groups.


Direct Standardization of rates

1. choose a standard population
2. multiply specific rates from pop#1 by standard pop age groups 3. sum the pop#1 and divide by total standard pop, then repeat for #2. ADJUSTS FOR CONFOUNDING EFFECT 

Protortionate Mortality Ratio (PMR)

observed deaths in population A/expected deaths based on the proportion in the population B.
Used when actual population numbers are not known. NOTE: NOT rates or risks 

Crude Birth rate

#live births in a year/average midyear population x 1000


crude death rate

#deaths in a year/ave midyear pop x 1000


Agespecific death rate

#deaths in certain age in a year/ave pop in age group x 100


causespecific death rate

#deaths from cause/midyear pop x 1000
