Surveillance Flashcards
What is epidemiology used to determine
Problem in a population
Risk factors of a disease
Change in disease outcome after intervention
Definition of epidemiology
The study of distribution and determinants of health conditions or events in a specific population
Takes in the consideration person place and time
Body of knowledge and method of study
Epidemiological triangle
Host
Environment
Agent
NOT TIME
All if these elements can influence the occurrence of disease
What is incidence
The number of new cases of a disease in a given time period and multiplied by a constant
NEW CASES - Prevalence is New and Old
Number of newly diagnosed cases of active TB in a calendar year in a given county.
What is a incidence density rate
It is another type of incidence rate in which time such as device days are patient days is incorporated into the denominator
Usually used in cohort studies
What is crude mortality rate
Crude mortality rate measures the proportion of the population during each year from all causes
What are the most commonly used rates and surveillance programs for healthcare settings
Incident
attack incident
density
prevalence
Attack rate
new cases/population at Risk x 100
Attack rate is a type of incident rate
Used for epidemics or outbreaks of disease
Frequency of new cases. Probability of becoming a case.
Condition in a specific population during a time period.
What is prevalence
The number of cases events or conditions occurring in a population
Old or new cases
Incidence is different because it’s only New cases
Example: census 487. 7 pts have pseudomonas calculate the prevelance rate.
Number of active TB cases in a county
of existing cases/ population during time period x 100
What is an endemic
Presence of a disease or condition of the specific population or geographical area
What is an epidemic
More cases of a disease that is expected in a given area for people over certain amount time
synonym - outbreak
What is a pandemic
An epidemic spread over why geographical area are countries
What is a reservoir
Replace one infectious agent can survive but not multiply
What is a fomite
Inanimate object in which an organism may exist for some period of time
What is heard immunity
Resistance of a group to invasion of the spread of an infection based on immunity of the population
What is artifactual association
False association that can be due to a chance or bias in the study method
What is indirect association
Mixing of effects of Effects among disease and a third factor that is associated with the exposure and independently affects the outcome
What is casual association
Evidence indicates that a factor clearly increases the probability of the occurrence of a disease and reduction of this fact or decreases the frequency of the disease
What is the strength of association in causality
The incidence of disease should be higher in those who are exposed to the factor under consideration
What is quantitative research
Transitional Scientific methods
Seeks to establish casual relationships
Use the statistics to test the strength and significance of the relationship in the study
What is qualitative research
Research that seeks to provide understanding of human experiences perceptions behaviors
What are the two types epidemiological studies - quantitative research
Observational studies - investigator doesn’t intervene
experimental studies- controls certain factors in the study
What are the two types of observational studies
Descriptive- characterize a population by occurrence of an outcome of time, place, person.
Analytic studies-compare individuals with or without an outcome with the presence of one or more risk factors
What are the three analytic studies
Cross-sectional
case-control
cohort
What is a cross-sectional study
I’ll come and rest factors are reviewed in a population at one point in time outcomes are measured (incident rates are not determined)
What is a case-control study
Population of individuals with and without an outcome of interest studied for exposure to one or more risk factors
studies are quicker and less expensive and easier
Example retrospective study
What is a cohort study
Start with a sample of individuals with and without exposure to potential risk factor for followed for incidents of the outcome in each group
strong evidence of casual association
Less pt selection
Example, 100 kids were monitored for colds during winter. Some had asthma, colds, or neither.
Name 5 data gathering techniques in qualitative research
Focus groups Participants observation Interviews Field notes Tape recording
Descriptive statistics
Data analysis that helps show, describe, or summarize, the data in a meaningful way such that patterns might emerge from the data.
Can’t make any conclusions from the data
Descriptive statistics
Numerical information about variables
uses numbers to describe characteristics of the data set
Inferential statistics
Differentiate between two groups
Can choose a subset of a population
Inferential statistics
Make an assumption about a population based on a sample of the population
Name three types of frequency distribution
Normal distribution - bell shape curve, mean, median, and mode are all equal
Skewness- asymmetrical distribution. Curve left - negative. Curve right - positive
Kurtosis- how flat or peaked a curve is
What is rate
Frequency with which an event occurs in a population
Measures of association
2x2 table
Relative risk- probability of developing a disease estimates how likely the disease is to occur.
Odds ratio-probability of having the risk factor. Looks at prevalence. Used for retrospective or cross sectional studies.
What is Mean
Central tendency
Average of values in a data set
Add numbers together and divide
Value is affected by outliers.
8+2+4+12+10 = 36 36/5 = 7.2
What is median
A value this divides the the data into 2 groups.
Value of the median is not affected by outliers
3,3,5,9,11. Median is 5
6,7,9,11,12,15. Median is 10
What is mode
Value in data set that occurs most frequently
Most useful for qualitative data
Least stable of mean,median, mode
1 3 6 6 6 6 7 7 11
6 is the mode
What is the p value
Probability
Probability of having committed a type I error
Helps determine the significance of your results
Small p value o.05 week evidence against the bulk hypothesis - accept
High p values likely a true null
P value of 0.04 week evidence
4%
What is null hypothesis
No effect of the research on a group
No difference
Confidence interval
Estimated range of values that is likely to include an unknown population
Calculated as 95% but could be 90, 99, or 99.5
Graphs
Y axis shows frequency Vertical
X Axis shows time interval horizontal
4 ways to test for reliability
Sensitivity % of persons with true positive results
Specificity- % of persons with true negative results
Positive predictive value- % of test + when disease is present
Negative predictive value- % of tests that are negative when disease is not present.
Components,of initial outbreak investigation
Confirm presence Alert key partners Lit review Case definition Methodology for case finding Line list or Epi curve Observe pt care Environmental sampling Control measures
Pneumonia
Early onset within first 4 days of hospitalization, caused by moraxella catarrhal is, haemophilus influenza, streptococcus pnemoniae
Late onset caused by gram neg bacteria or SA, MRSA, viruses, yeasts. Fungi,
Clinically defined pneumonia
Two or more CXR with one of the following.
Infiltrate
Consolidation
Cavitation
Pneumatoceles infants < 1
What type of transmission occurs in s point source epidemic?
A vehicle
Could be a single meal or event
Rises quickly and falls gradually
How is the specificity of a test for infection or disease defined?
Total # of persons without disease
What is Range (variability)
Difference between the smallest number and the largest number,
2,4,5,6,9,10,11,15,18
16 is the answer
What is variability
Measures how the values are spread around the main and includes range, deviation, standard deviation, and variance
What does it mean when a test has a higher specificity?
A negative result will be more accurate than a positive
Frequency Polygon uses:
Shows 2 sets of data on a single graph
Uses lines and points
Uses histogram
What is the Chi square test used for?
To evaluate the effect of a variable on outcomes
To calculate an odds ratio or relative risk
If each cell of the table is greater than 5
What are SPC (statistical process control) charts used for
Monitor the process of care
Facilitate the determination of variation
Monitor outcomes
DOES NOT eliminate natural variation
Statistical Process Control
Use an upper and lower control limit - beyond those limits is out of range
Useful in showing changes in rates
Less stable with small denominators
AKA control chart
Monitor quality assurance
Confounding variable
extraneous variable even that systematically varies with the independent variable and influences the dependent variable
What can cause bias in a study
Instrument
Observer
Data collection method
Case and control group selection
Hill’s criteria for causation
Strength Consistency Specificity Temporality Biological gradient Plausibility Coherence Experiment Analogy
Strength of association
Incidence of disease should be higher in those who are exposed to the factor under consideration than those who are not exposed
Consistency
Association should be observed in numerous studies by different researchers
Specificity
Association between one factor and on disease, this is more casual
The ability of a test case definition or surveillance system to exclude persons who do not have the health condition of interest
Biological gradient
Dose response relationship between increased exposure to a factor and increased likelihood of disease.
Enzootic
Presence of disease among animals within a geographical area.
Epizootic
Excess over the expected extent of disease within an animal population in a geographical area during a specified time period.
Zoonosis
Disease transmitted from animals to humans
Descriptive study
Simplest observation study
Describes person, place, or time
Generate rates or identify populations at risk.
Can’t show causality.
Using GRAPHS to present data
Quantitative dats using system coordinates
Two sets of lines that intersect at right angles
More than one variable can be shown on a graph
X axis variable of time (year, month, quarter)
Y axis reflects frequency (# of cases)
Presenting data in tables
Tables used to present data in rows & columns.
Frequency of events
Provide information on person, place, and time
Arithmetic line graph
Equal distances along the Y axis
Semi logarithmic scale
Used H axis measures in logarithms of units.
Histogram
Graphic of a frequency distribution in which one bar is used for each time interval
there is no space between intervals
Area on graph uses two rectangles
Epidemic curve
Frequency polygons
Place data points over the center point of the data range.
Bars are connected
Frequency Polygon
Similar to a line graph
Each coordinate point represented by a point displayed on the graph with straight line connecting them.
Provides the same data as histogram
Data displayed in charts
Uses one coordinate Compare parts of a total picture Bar charts Geographical coordinates Pictograms Pie charts
Device ratio
of device days/# patient days = device utilization ratio
What is sensitivity
The ability of a test case definition or surveillance system to identify true cases or persons who have the health condition of interest
What is a pseudo outbreak
Rise in test results without clinical disease
Positive microbiology results
What is standard deviation
Standard deviation is a measure of dispersion I have the raw scores that reflect variability and values around the mean
P
Standard deviation indicates how small the variability is among observations
If variability is small, values are close to the mean
Large values are not close to the mean
If results are normally distributed 68% of them will be within standard deviation of the mean
Type I error
Rejects the null hypothesis when it’s true attributing significance when there is none.
Type I error is referred to as the significance level
Keeping the level small 0.05 0.01 will decrease the risk of committing a type I error.
Type II error
Accepting the null hypothesis when it is false or not attributing significance when it exists.
Type II error can be avoided by increasing the sample size
When is the Fishers test used?
Statistical test used when data numbers are low
SMALL SAMPLE SIZE
z test
Most appropriate to test that the means of two samples are not different two-tailed hypothesis
Example used to compare the mean of infection rates again and NHSN mean
sample size should be at least 30
What is that T test
It’s used for continuous data on the sample size is less than 30 can be one or two tail
What is true if prevalence of disease is very low?
Positive predictive value of a diagnostic test is lowered
