Segars: Epidemiology Flashcards
What is epidemiology?
- a public health-discipline basic science which studies the…
- distribution
- determinants
- … of disease in populations to control disease and illness, and promote health
What are the 3 W’s of patterns of disease ocurrences?
- Who
- Where
- When
- this is descriptive epidemiology
What can descriptive epidemiology be used for?
-to know if a location is experiencing disease occurrence more frequently than usual or more than other locations
What are the 3 key factors in comparing measures of disease frequency between groups
- # of people affected/impacted (frequency/count)
- Size of the source population (from which disease cases or outcomes arose) or those at risk
- Length of time the “population” is followed
Passive surveillance system?
-relies on healthcare system to follow regulations on required reportable diseases/conditions
Active surveillance system
-public health officials go into communities to search for new disease/condition cases
Syndromic surveillance system
-a system that looks for pre-defined signs/symptoms of pts related to trackable-but-rare diseases/conditions
What is an epidemic
-occurrence of disease clearly in excess of normal expectancy
What is an outbreak
- an epidemic limited to a localized increase in the occurrence of disease
- sometimes interchanged with “cluster”
Endemic
-the contant presence of a disease within a given area or population in excess of normal levels in other areas
Emergency of international concern
-an epidemic that alerts the world to the need for high vigilance (pre pandemic)
Pandemic
- an epidemic spread world-wide (global health)
- multi national/ multi continent
What are some epidemiological assumptions?
- disease occurrence is not random
- systematic investigation of different populations can identify associations and causal/preventive factors and impact of changes can impart on health of population
- making comparisons is the cornerstone of systematic disease assessments/investigations
What are the determinants of disease?
- factors of susceptibility/exposure/risk
- etiology/causes of disease
- Modes of transmission
- social/environmental/biologic elements that determine the occurrence/presence of disease
What are the 3 types of frequencies utilized to measure disease frequencies?
- proportions: division of 2 related numbers (the numerator is a subset of the denominator)
- Ratios: division of 2 unrelated numbers (numerator is not a subset of the denominator)
- Rates: division of 2 numbers with time included in the denominator
What is incidence
-NEW occurrences of an outcome/disease
What is prevalence
- EXISTING occurrences of an outcome/disease
- includes old and new cases, collectively
What are both incidence and prevalence?
- a proportion!
- a simple percentage
- part over whole
What is the formula for incidence?
- # of new cases of illness/# of people at risk of illness
- ALWAYS subtract out (from the starting population), those who not at risk (already have the disease or are immune)
What is the formula for prevalence?
- total # of cases of illness/# of people in population
- remember that there is point prevalence and period prevalence
What is infectivity
- the ability to invade a patient (host)
- #infected/# susceptible (at risk)
Pathogenicity?
- the ability to cause clinical disease
- # with clinical disease/ #infected
What is virulence
- the ability to cause death
- # of deaths/# with infectious disease
- synonymous with case-fatality rate
What is crude morbidity rate?
-# of persons with disease/ # of persons in population
Crude mortality rate?
-# of deaths (all causes)/# of persons in population
Cause-specific morbidity rate?
-# of persons with cause-specific disease/# of persons in population
Cause-specific mortality rate?
-# of cause-specific deaths/# of persons in population
case-fatality rate
-# of cause-specific deaths/# of cases of disease
What is risk?
- the probability of an outcome in a specific group
- remember that 2x2 square thing…. exposure vertical and outcome horizontal
What is absolute risk reduction
- AR defines the risk difference of the outcome attributable to exposure difference between groups
- ex: difference in MI’s between the rampril and placebo group
Relative risk reduction (RRR)
-ARR/Runexposed
What is Number needed to treat or the number needed to harm (NNT/NNH)
- on average, the # of pts needed to be treated to receive the stated benefit/harm
- 1/absolute risk reduction (ARR)… indecimal format
- ex: 1/0.038= 27 pts would need to be treated with ramipiril to reduce 1 AMI/CVA/Death from CV causes
- remember to always round up to the next “whole” person (value)
What is Risk ratio?
- ratio of the risks from 2 different groups
- risk of outcome in exposed/risk of outcome in non-exposed
What is odds
- a ratio
- FREQUENCY of an outcome occurring vs. NOT occurring in a specific group
- NOT a simple percentage, it’s a ratio
What is Odds ratio (OR)?
- ratio of the odds from 2 different groups
- Odds of exposure (in diseased)/odds of exposure (in non-diseased)
- **you can also cross multiply in the 2x2 table; same answer (AxD/BxC)
What does it mean when the ratio is >1.0?
-the event/outcome is more likely to occur in the comparison group (numerator group)
What does it mean when the ratio is <1.0?
-the event/outcome is less likely to occur in the comparison group (numerator group)
If RR is 1.53, what does that mean?
-the comparator group is 53% increased risk
If ratio is >2.0 , what do we say?
- if OR= 6.18
- we say it’s 6.18 greater odds
What do we say if HR= 0.73?
-then the comparatory group has a 27% decreased probability of the hazard outcome
What do we look for when interpreting Ratio’s?
- group comparison orientation
- direction of words
- magnitude
What was the thing in the red box about the confidence interval (CI)?
-when looking at the CI for “ratios”, if both values are on the SAME SIDE of 1.0, it is always statistically significant
