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CIC SURVEILLANCE AND EPIDEMIOLOGIC INVESTIGATION
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1. Identify the median in the following list of numbers: 6, 2, 9, 7, 1, 4
a. 9
b. 7
c. 5
d. 4
C 5
Rationale: The median of a data set is the number that 50 percent of values fall below and 50 percent of values fall above. The data here are not presented in numerical order so first they must be ordered from lowest to highest: 1, 2, 4, 6, 7, 9.
There is an even number of values in this set so to find the median one must identify the two central numbers and then average them. The two central numbers are 4 and 6; 4 + 6 = 10 and 10/2 = 5.
2. In a study of whether Operating room A (OR A) is associated with a higher number of surgical site infections (SSIs) than Operating room B (OR B), the infection preventionist (IP) is testing whether:
Ho: OR A SSI rate = OR B SSI rate
Ha: OR A SSI rate ≠ OR B SSI rate
The IP concludes that the SSI rate in OR A is not equal to the SSI rate in OR B, but in reality the two rates are equal. What type of statistical error has she committed?
a. No error has been committed
b. She committed a Type I error
c. She committed a Type II error
d. She committed an error equal to β
B She has committed a Type I error
Rationale: If the IP concluded that the SSI rate in OR A is not equal to the SSI rate in OR B, then she rejects the null hypothesis. However, in this case the null hypothesis was true; therefore she has committed a Type I error. This value is equal to α.
3. For which of the following procedure(s) is the surveillance period for deep incisional or organ/space SSI 90 days?
1) Cesarean section
2) Craniotomy
3) Coronary artery bypass graft
4) Laminectomy
a. 1, 2
b. 2, 3
c. 3, 4
d. 1, 4
B 2, 3
Rationale: According to the Centers for Disease Control and Prevention (CDC) SSI surveillance definitions, postoperative surveillance for deep incisional or organ/space SSIs should be conducted for 90 days on craniotomy and coronary artery bypass procedures. Superficial incisional SSIs are only followed for a 30-day period for all procedure types.
4. An appropriate indicator to monitor process compliance would be:
a. Class 1 SSI rate
b. Appropriate antibiotic dosage
c. Central line-associated bloodstream infections (CLABSIs) in the Neonatal Intensive Care Unit (NICU)
d. Infections caused by multidrug-resistant organisms
B Appropriate antibiotic dosage
Rationale: A surveillance program should monitor a variety of outcomes, processes, and events, and some indicators should focus on personnel.
5. What key infection control activity is defined as the Systematic, ongoing collection, management, analysis, and interpretation of data followed by the dissemination of these data to public health programs to stimulate public health action?
a. Research
b. Surveillance
c. Benchmarking
d. Accreditation
B Surveillance
Rationale: Surveillance has been defined as the ongoing collection, collation, and analysis of data and the ongoing dissemination of information to those who need to know so that action can be taken." Surveillance is an essential component of an effective infection prevention and control program. Surveillance includes the collection of data with the ultimate objective of dissemination of that data to support and improve public health activities.
6. An IP is reading a journal article that states that the data the authors collected are normally distributed. What does this mean?
a. When the data are plotted on a curve, it is skewed
b. The mean is less than the median
c. The skewness value is equal to 1
d. The mean, median, and mode of the data are equal
D The mean, median, and mode of the data are equal
Rationale: If the data are normally distributed, then the mean, median, and mode are all equal and the curve will have a bell shape, with most observations clustering at the center and then tapering off on either side of the center.
7. Which of the following is indicative of a superficial SI?
a. Pain at the incision site 10 days after a breast reduction procedure; drainage is culture-positive for methicillin- susceptible Staphylococcus aureus (MSSA)
b. Stitch abscess that is cultured 14 days after surgery and is positive for Enterococcus faecalis
c. Purulent drainage from an episiotomy that occurs within 5 days of delivery
d. Burn wound that cultures positive for Acinetobacter baumannii 10 days after debridement procedure
A Pain at the incision site 10 days after a breast reduction procedure; drainage is culture positive for methicillin-susceptible Staphylococcus aureus (MSSA)
Rationale: SSI continues to be a major source of morbidity, economic cost, and even death in surgical patients. To meet the criteria for a superficial SI, the infection must occur within 30 days after the operation and involve only skin or subcutaneous tissue. In addition, one of the following must be met:
• Purulent drainage, with or without laboratory confirmation, from the superficial incision
• Organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision
• And patient has at least one of the following:
° Purulent drainage from the superficial incision
° Organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision
° Superficial incision that is deliberately opened by a surgeon, attending physician, or other designee
And patient has at least one of the following signs or symptoms: pain or tenderness, localized swelling, redness, or heat. A culture negative finding does not meet this criterion.
° Diagnosis of superficial incisional SI by the surgeon or attending physician or other designee
8. An IP is preparing the quarterly report for the Infection Control Committee. What information will be needed to calculate a CLABSI rate for the ICU?
1) The total number of patients in the unit for the time period
2) The total number of central line catheters for the time period
3) The number of patients who had bloodstream infections identifie
4) The number of device days for the time period
a. 2, 3
b. 1, 3
c. 1, 2
d. 3, 4
D 3, 4
Rationale: The numerator would be the number of patients who had bloodstream infections identified and who had a central line during the time period. The denominator would be the number of device days (at the same time every day, count the number of patients with one or more central lines) for the time period.
Basic Formula for All Types of Rates
• Rate = x/y × k
Where:
• x = The numerator, which equals the number of times the event (e.g., infections) has occurred during a specified time interval
• y = The denominator, which equals a population (e.g., number of patients at risk) from which those experiencing the event were derived during the same time interval
• k = A constant used to transform the result of division into a uniform quantity so that it can be compared with other, similar quantities. A whole number (fractions are inconvenient) such as 100, 1,000, 10,000, or 100,000 is usually used (selection of k is usually made so that the smallest rate calculated has at least one digit to the left of the decimal point) or is determined by accepted practice (the magnitude of numerator compared with denominator).
9. What type of rate would the IP want to calculate to give feedback to the surgeons at her facility?
a. Procedure-specific
b. Provider-specific
c. Unit-specific
d. Device-specific
B Provider-specific
Rationale: Providing feedback of appropriate SSI surveillance data to surgeons has been shown to be important to reducing SSI risk. Furthermore, providing active rather than passive feedback of surveillance results to surgeons has the greatest effect in reducing SSI rates. When surgical teams are engaged in examining their SSI rates and in appraising clinical processes, there is greater probability of success in reducing infection rates.
10. The IP has been benchmarking her data to other facilities performing similar activities for a period of time. The IP should analyze the entire process to ensure that which of the following conditions are met?
1) Standardized definitions ae used consistently
2) Overall rates are used to accurately track trends over time
3) Adequate training of personnel to collect, store, manage, and analyze data
4) Data are calculated using the same methodology as a nationally validated system
a. 1, 2, 3
b. 2, 3, 4
c. 1, 3, 4
d. 1, 2, 4
C 1, 3, 4
Rationale: To accurately trend surveillance data over time within a facility or compare rates between facilities, surveillance criteria (i.e., case definition) must be consistently used to determine the presence of an HAI, occurrence of an event, or compliance with a process. Rates, rather than raw numbers, must be used to accurately track trends over time. Personnel who are responsible for collecting and managing surveillance data must have adequate training in reviewing medical records, interpreting clinical notes, applying standardized criteria for identifying cases, using appropriate statistical and risk adjustment methods, and using computer tools and technology (especially electronic records, spreadsheets, and databases) to collect, store, manage, and analyze data. Whenever possible, data should be expressed as rates or ratios that are calculated using the same methodology as a nationally validated surveillance system. This allows an organization to compare its rates with another organization or a recognized benchmark.
11. The chi-square test can be used:
1) To evaluate the effect of a variable on outcomes
2) To analyze continuous data
3) To calculate an odds ratio or relative risk
4) If each cell of the table is greater than 5
a. 1, 2, 3
b. 1, 2, 4
c. 2, 3, 4
d. 1, 3, 4
D 1, 3, 4
Rationale: Chi-square tests (χ2) can be used to test the association between two classifications of a set of counts or frequencies (discrete data). This data are commonly displayed as a contingency table or 2 x 2 table where rows represent one variable and columns represent the other. The null hypothesis is that there is no association between the two variables. Row and column totals (marginal totals) are used to predict what count would be expected for each cell if the null hypothesis were true. A test statistic is calculated from the observed and expected frequencies. The larger the test statistic (for given degrees of freedom) the more likely there is to be a statistically significantassociation between the two variables. Chi-square tests are used for medium to large samples (see Figure 4-1). The Fisher's exact test is used in place of the χ2 when the sample size number is less than 20 or any one cell in the table is less than 5.
12. The measure of central tendency most affected by outliers is:
a. Mean
b. Median
c. Mode
d. Range
A Mean
Rationale: Measures of central tendency describe how observations cluster around a middle value and locate only the center of a distribution measure. The methods include mean, median, and mode. The most commonly used parameter is the arithmetic mean (average). The mean of a data set is inaccurate if there are extreme values (outliers) in a data set. Most statistical tests use the mean because it is more amenable to mathematical manipulation than the median or the mode. However, because the mean includes the value of each observation, it is the measurement most affected by outliers (unusually high or low values), especially when the number of observations is small. As the sample size gets very large, outliers are less important.
13. The p value in statistical test results indicates:
a. Causation
b. The probability of having committed a Type I error
c. The probability of having committed a Type II error
d. The probability of data being accurate and valid
B The probability of having committed a Type I error
Rationale: A Type I error occurs when one rejects the null hypothesis (H0) when it is true. This is also called a false-positive result (as we incorrectly conclude that the research hypothesis is true when in fact it is not). The p value or calculated probability is the estimated probability of rejecting the null hypothesis of a study question when that hypothesis is true.
14. On a normally distributed data set, what percentage of values lies within three standard deviations from the mean?
a. 68.2
b. 95.5
c. 92.4
d. 99.7
D 99.7
Rationale: Standard deviation is a measure of dispersion of the raw scores that reflects the ariability in values around the mean. It employs the squared deviations from the mean (variance), which therefore gives added emphasis to larger deviations. The standard deviation indicates how small the variability is (i.e., the spread) among observations. If the variability is small, all the values are close to the mean. If it is large, the values are not close to the mean. The significance of the standard deviation is that with normal (bell-shaped) distributions, the following empirical rules for the normal curve apply:• The interval from one standard deviation below the mean to one standard deviation above the mean contains approximately 68 percent of the measurements.• The interval from two standard deviations below the mean to two standard deviations above the mean contains approximately 95 percent of the measurements.• The interval from three standard deviations below the mean to three standard deviations above the mean contains approximately 99.7 percent (or approximately all) of the measurements.
15. Which statistical test is used when the data are small in numbers?
a. Fisher's exact
b. t test
c. Chi-square
d. z test
A Fisher's exact
Rationale: Fisher's exact test is a statistical significance test used in the analysis of contingency tables. Although in practice it is employed when sample sizes are small, it is valid for all sample sizes.
16. Statistical process control (SPC) charts are used for all of the following purposes except:
a. Monitor the process of care
b. Facilitate the determination of variation
c. Eliminate natural variation
d. Monitor outcomes
C Eliminate natural variation
Rationale: SPC is a method of quality control that uses statistical methods and is an essential component of quality assurance and performance improvement. The principles of statistical process control are used to monitor both processes and outcomes in a systematic and statistically valid manner. Control charts can assist in determining special-cause or common-cause variations, which may be helpful for early detection of abnormal events.
17. Seventy-fie patients were admitted to the Medical-Surgical ICU. Forty were on the surgical service and 35 were on the medical service. Fifteen patients developed a healthcare-associated infection with methicillin-resistant Staphylococcus aureus (MRSA). Nine of the patients with MRSA infection were on the surgical service. There were 230 patient days in the ICU for the surgical patients in January, and 325 patient days for medical patients. What was the incidence density of MRSA attack infection for patients on the surgical service?
a. 29 infections per 1,000 patient days
b. 26 infections per 1,000 patient days
c. 19 infections per 100 patient days
d. 39 infections per 1,000 patient days
D 39 infections per 1,000 patient days
Rationale: The incidence rate is the number of new cases per population at risk in a given time period. When the denominator is the sum of the person-time of the at-risk population, it is also known as the incidence density rate or person-time incidence rate. The incidence-density rate for this scenario is 9 (new cases of MRSA) ÷ 230 (total number of patient days) x 1,000 = 39.13 (round to 39) infections per 1,000 patient days.
18. Plague is endemic in parts of the Southwest United States. The word "endemic" means:
a. Natives are immune to plague
b. An expected number of cases occurs each year in a given geographical area
c. Plague has become resistant to all forms of treatment for this population
d. The disease is seen in a seasonal pattern each year for this area
B An expected number of cases occurs each year in a given geographical area
Rationale: The term "endemic" refers to the usual incidence of a given disease within a geographical area during a specified time period
19. A pandemic differs from an epidemic in that:
a. Only one disease is involved
b. It is usually vectorborne
c. There is a higher mortality rate
d. Several countries or continents are involved
D Several countries or continents are involved
Rationale: The term "pandemic" refers to an epidemic of disease spread over a wide geographical area across countries or continents.
20. Specificity of a test for infection or disease is calculated as:
a. The number of true negatives divided by the number of positives found, times 100
b. The number of true negatives divided by the total number of persons with disease, times 100
c. The number of true positives divided by the total number of persons with disease, times 100
d. The number of true negatives divided by the total number of persons without disease, times 100
D The number of true negatives divided by the total number of persons without disease, times 100
Rationale: Sensitivity (also called the true positive rate) measures the proportion of actual positives that are correctly identified as such e.g., the percentage of sick people who are correctly identified as having the condition). Specificity sometimes called the true negative rate) measures the proportion of negatives that are correctly identified as such e.g., the percentage of healthy people who are correctly identified as not having the condition).
Specificity = true negatives ÷ True negatives + False positives
21. A measure of dispersion that reflects the ariability in values around the mean is called the:
a. Variance
b. Standard deviation
c. Range
d. Bell curve
B Standard deviation
Rationale: Measures of dispersion describe the degree of variation or dispersion of values in a population or in a sample. Measures of dispersion are a type of descriptive statistic. Measures of dispersion include the range, deviation, standard deviation, and variance. Standard deviation is a measure of dispersion of the raw scores that reflects the variability in values around the mean. The standard deviation indicates how small the variability is (i.e., the spread) among observations. If the variability is small, all the values are close to the mean. If it is large, the values are not close to the mean.
22. In any normal distribution, the proportion of observations that are within two standard deviations of the mean is closest to:
a. 0.50
b. 0.68
c. 0.95
d. 0.98
C 0.95
Rationale: Standard deviation is a measure of dispersion of the raw scores that reflects the variability in values around the mean. The significance of the standard deviation is that with normal (bell-shaped) distributions, the following empirical rules for the normal curve apply (see Figure 4-2):• The interval from one standard deviation below the mean to one standard deviation above the mean contains approximately 68 percent of the measurements.• The interval from two standard deviations below the mean to two standard deviations above the mean contains approximately 95 percent of the measurements.• The interval from three standard deviations below the mean to three standard deviations above the mean contains approximately 99.7 percent (or approximately all) of the measurements.
23. The most important feature of nonparametric tests is that they:
a. Make no assumption about variance in the populations
b. Can only be used with ordinal levels of measurements
c. Require a normal distribution
d. Require equal population variances
A Make no assumption about variance in the populations
Rationale: Nonparametric data make no assumption about the distribution of the population values and can be used with discrete data (e.g., infection, no infection), nominal and ordinal data, and interval data. The main advantage of nonparametric methods is that the assumptions of normality are not required.
24. Which of the following indicates a strong positive correlation?
a. r = 0
b. r = -0.993
c. r = 0.603
d. r = 0.45
C r = 0.603
Rationale: Correlation is a statistical technique that shows whether pairs of variables are related. Correlation calculates a value, r, that measures the degree (strength) of the relationship. The calculated values can range between +1 and -1. The closer r is to ±1, the stronger the relationship. A positive correlation exists when one variable increases and causes the other to increase as well (e.g., the longer a urinary catheter is in place, the greater the risk of developing a urinary tract infection). A negative correlation occurs when one variable increases and causes the other to decrease (e.g., increased hand washing results in fewer infections). The association between two variables decreases as r approaches 0 (with a value of 0, there is no correlation).
25. The Employee Health Service has notified the IP tht seven employees have P. aeruginosa folliculitis. Initial investigation reveals that six of the seven cases belong to the same health club. Working on the hypothesis that the whirlpool at the health club is associated with the infections, the IP decides to conduct a case-control study using two controls for each case. Which of the following groups is the most appropriate control?
a. Non-ill family members of the ill employees
b. Non-ill hospital employees matched for age and sex
c. Hospitalized patients with P. aeruginosa folliculitis matched for age and sex
d. Non-ill members of the health club matched for age and sex
D Non-ill members of the health club matched for age and sex
Rationale: Case-control studies begin with the identification of persons who have the outcome of interest. Then a control group of individuals without the outcome is selected for comparison. The selection of an appropriate control group is critical in that control patients must not only have the outcome of interest but also should be similar to the cases in the potential for exposure during the period of risk being evaluated. Controls are matched to cases on one or more attributes (i.e. age, gender, smoking status, etc.). Each case/control pair then has identical values on the matching factors. Therefore, the most appropriate controls would be non-ill members of the health club.
26. Which of the following steps are not included in hypothesis testing?
a. State the null and alternative hypotheses
b. Set the significance level
c. Eliminate outliers
d. Compare the probability value to the significance level
C Eliminate outliers
Rationale: A common use of statistics is hypothesis testing. It is a statement of expected results. Hypothesis testing uses the distribution of a known area in the normal curve. It estimates the likelihood (probability) that a result did not occur by chance.
Steps to hypothesis testing include:
• State the research question
• Specify the null and alternative hypotheses
• Calculate test statistic
• Compute probability of test statistic or rejection region
• State conclusions
Outliers are observations that deviate from all others significantly. They may occur by accident or they may be results of measurement errors. Analysis and dealing with outliers is an important component of statistical analysis. Sometimes careful analysis of outliers, their removal, or weighting down can change the conclusions considerably. Outliers should be investigated to determine the optimal method of analysis.
27. The range of the correlation coefficient is
a. -1 to 0
b. 0 to 1
c. -1 to 1
d. None of the above
C -1 to 1
Rationale: Correlation is used to calculate the direction and magnitude of a relationship between two variables. Correlation calculates a value, r, that measures the degree of the relationship. The calculated values can range between +1 and -1. The closer r is to ±1, the stronger the relationship. A positive correlation exists when one variable increases and causes the other to increase as well (e.g., the longer a urinary catheter is in place, the greater the risk of developing a urinary tract infection). A negative correlation occurs when one variable increases and causes the other to decrease (e.g., increased hand washing results in fewer infections). The association between two variables decreases as r approaches 0 (with a value of 0, there is no correlation).
28. If the index of kurtosis is -1.99, then the curve is:
a. Relatively flat
b. Negatively skewed
c. More peaked
d. A typical bell-shaped curve or normal distribution
28. A Relatively flat
Rationale: Two terms are used to describe the shape of a frequency distribution: "skewness" and "kurtosis."
Kurtosis refers to how flt or peaked a curve is (see Figure 4-3):
• Mesokurtic is a typical bell-shaped curve or normal distribution.
• Leptokurtic is the more peaked curve.
• Platykurtic is the flatter curve.
Statistical packages calculate kurtosis. A value of 0 indicates mesokurtosis, positive numbers indicate leptokurtosis, and negative numbers indicate platykurtosis.
29. The IP monitors all patients who have coronary artery bypass graft surgery for infections and pneumonia. The probability or likelihood of an event occurring is the:
a. Risk
b. Attack rate
c. Host factor
d. Incidence
A Risk
Rationale: In epidemiology, risk is defined as the probability that an event will occur (e.g., that an individual will become ill or die within a stated period of time or age).
30. When a study is completed, a report should be written to give the results and evaluation of the study. A good way to display data is by charts or tables. A table is used to illustrate data:
a. Using only one coordinate
b. Arranged in rows and columns
c. Using a system of coordinates
d. Showing multiple complex factors at one time
B Arranged in rows and columns
Rationale: A table is an organized set of data elements (values) that uses a model of vertical columns (which are identified y their name) and horizontal rows. The cell is the unit where a row and column intersect. A table has a specified number of columns, but can have any number of rows. Each row is identified y the values appearing in a particular column subset that has been identified as a unique key index.
31. Calculate the mode for the following set of numbers: 2, 11, 5, 21, 3, 11, 8, 26
a. 24
b. 10.8
c. 11
d. 9.5
C 11
Rationale: The mode represents the observation(s) that occur(s) most frequently in a data set and determines the height and shape of a curve. Data sets may have more than one mode and can be bimodal or multimodal. Small data sets may be nonmodal (e.g., there are no repeated values). The mode is most useful for describing qualitative data and is used for nominal data and bimodal distributions. It is the least stable of the three measures of central tendency. The mode for this set of numbers is 11, as it occurs most frequently.
32. As the sample size increases, how is the power of the study affected?
a. Power is independent of sample size
b. Power is increased
c. Power is decreased
d. Power approaches 0
B Power is increased
Rationale: The power of a test is its ability to detect a specified difference (e.g., the probability of rejecting the null hypothesis when it is false). The power of a hypothesis test is affected by three factors:
1. Sample size (n). In general, the greater the sample size, the greater the power of the test.
2. Significance level (α). The higher the significance level, the higher the power of the test.
3. The "true" value of the parameter being tested. The greater the difference between the "true" value of a parameter and the value specified in the null hypothesis, the greater the power of the test. That is, the greater the effect size, the greater the power of the test.
33. The term for an extraneous variable that systematically varies with the independent variable and influences the dependent variable is a:
a. Predictor variable
b. Moderating variable
c. Experimental variable
d. Confounding variable
D Confounding variable
Rationale: A confounding variable is a variable that has an important confounding effect on the result but is not among the variables being studied. It can suggest a false relationship between variables, or it can hide a relationship that exists.
34. When a normal distribution is graphed, which of the following are true?
1) There is a continuous, symmetrical distribution in which both tails extend to infinity
2) The mean, median, and mode are identical
3) 68.3 percent of the area lies between the mean and ±2 standard deviations
4) The shape of the curve is determined by the mean and standard deviation
a. 1, 2, 3
b. 2, 3, 4
c. 1, 3, 4
d. 1, 2, 4
D 1, 2, 4
Rationale: If the distribution (spread) of the values is even on both sides of the mean (both halves are equal), it is a normal distribution (see Figure 6-2). Properties of a normal distribution include:
• Forms a symmetric bell-shaped curve
• 50 percent of the scores lie above and 50 percent below the midpoint of the distribution
• The population clusters around a central point and then trails off symmetrically in both directions with fewer and fewer large and small individuals at the upper and lower ends, respectively
• Mean, median, and mode are located at the midpoint of the x axis
35. Which of the following is not considered one of the criteria for causality:
a. The incidence of disease is higher in those who are exposed to the factor
b. Evidence that the independent and dependent variables are related
c. The association has been observed in numerous studies
d. The onset of disease must precede exposure to the causal factor
D The onset of disease must precede exposure to the causal factor
Rationale: The criteria for causality are known as Hill's criteria and use epidemiological methods to determine whether a factor is causal for a given disease. Hill's criteria for causation are as follows:
1. Strength of association: The incidence of disease should be higher in those who are exposed to the factor under consideration than in those who are not exposed; that is, the stronger the association between an exposure and a disease, the more likely the exposure is to be causal. For example, lung cancer is common in those who smoke.
2. Consistency: This means that the association should be observed in numerous studies, preferably by different researchers using different research methodologies.
3. Specificity Refers to an association between one factor and one disease, and this association is more likely to be causal. This criterion also refers to the extent to which the occurrence of one factor can be used to predict the occurrence of another (disease). In reality, such a one-to-one relationship is rare due to the multifactorial causes of most diseases and because, sometimes, the same factor(s) can cause more than one disease.
4. Temporality: This must also be addressed when determining cause of disease. Essentially, exposure to the hypothesized causal factor must precede the onset of disease.
5. Biological gradient: The biological gradient is a dose-response relationship between increased exposure to a factor and increased likelihood of disease. For example, the longer one smokes, the more likely one is to develop lung cancer. If the association demonstrates a biological gradient between the factor (exposure) and effect (disease), the relationship is more likely to be causal.
6. Plausibility: The association in question should also be biologically plausible in light of current knowledge. This criterion may be the most elusive and variable of the nine. Because biological knowledge is ever expanding, lack of biological plausibility does not necessarily disprove a theoretical association.
7. Coherence: There should be coherence between known information about the biological spectrum of the disease and the associated factor, that is, the association should be in accordance with other facts known about the natural history of the disease.
8. Analogy: Associations derived from experiments add considerable weight to evidence supporting causal associations. These experiments can be animal model studies or clinical trials; however, although animal models may be helpful, many diseases do not manifest the same way in animals and humans.
9. Finally, if similar associations have been shown to be causal, by analogy the association is more likely to be causal. Determining causality may also help to determine at which points the natural history of a disease may be interrupted, so that prevention and control efforts are effective. It can also add information on the natural history of a disease.
36. Which of the following are true about a frequency polygon:
1) Is useful for showing two sets of data on a single graph
2) Uses bars on the x axis
3) Uses connecting lines and data points
4) Depicts the percentage of the total that each data point represents
a. 1, 3
b. 1, 4
c. 3, 4
d. 2, 4
A 1, 3
Rationale: Graphic or pictorial statistics present the numerical data that have been collected in graphs or charts, creating a picture of the data. A frequency polygon (see Figure 4-4) is a graph of a frequency distribution with values of the variable on the x axis and the number of observations on the y axis; data points are plotted at the midpoints of the intervals and are connected with a straight line.
37. Targeted surveillance focuses on:
a. Tracking high-risk, high-volume procedures and potentially preventable healthcare-associated infections (HAIs)
b. Providing whole-house infection rates
c. Tracking infections that are publicly reported
d. Using the electronic surveillance systems to identify infections
A Tracking high-risk, high-volume procedures and potentially preventable healthcare-associated infections (HAIs)
Rationale: Targeted surveillance is one method used for HAI surveillance. Targeted surveillance focuses on particular units, invasive procedures, infections related to medical devices, and organisms of epidemiological significance.
38. The new IP for a long-term care facility is assessing adherence to the facility's hand hygiene policies. Which of the following should he include when reporting his finding?
a. The number of hand hygiene episodes performed by personnel divided by the volume of soap used in the facility
b. The number of hand hygiene episodes performed by personnel divided by the number of patient days times 1,000
c. The number of hand hygiene episodes performed by personnel divided by the volume of alcohol-based hand rub
d. The number of hand hygiene episodes performed by personnel divided by the number of hand hygiene opportunities by ward or service
D The number of hand hygiene episodes performed by personnel divided by the number of hand hygiene opportunities by ward or service
Rationale: The CDC guideline and the Joint Commission require that healthcare personnel adherence to recommended hand hygiene policies be monitored and that healthcare personnel be provided with information about their performance. Acceptable methods for measuring hand hygiene adherence include:• Periodically conduct an observational study to determine the rate of adherence (number of hand hygiene episodes performed/number of hand hygiene opportunities) by ward or service. In addition to monitoring the rate of adherence, facilities may also assess the quality of hand hygiene adherence (time spent per hand hygiene episode, whether soap was used, etc.)• Monitor the volume of specific hand hygiene products (e.g., soap, hand rub, hand lotion) used per 1000 patient days• Monitor adherence to artificial fingernail policies
39. Which of the following viruses is the causative agent in Kaposi's sarcoma?
a. Herpes zoster virus
b. Human herpesvirus 8
c. Epstein-Barr virus
d. Human papillomavirus (HPV)
B Human herpesvirus 8
Rationale: Kaposi's sarcoma is a tumor caused by human herpesvirus 8 (HHV8, also known as Kaposi's sarcoma-associated herpesvirus or KSHV). Kaposi's sarcoma (KS) is a systemic disease that can present with cutaneous lesions with or without internal involvement. KS lesions are nodules or blotches that may be red, purple, brown, or black and are usually papular. They are typically found on the skin, but spread elsewhere is common, especially the mouth, gastrointestinal tract and respiratory tract. Growth can range from very slow to explosively fast and is associated with significant
mortality and morbidity.
40. The IP receives a call from the ER about a 38-year-old male with a 4-week history of cough and fever. He has just returned from an extended trip to the southwestern United States. Coccidioidomycosis is on the list of possible diagnoses. Which of the following is true regarding the epidemiology of coccidioidomycosis?
a. Coccidioides spp. are usually found at high elevations
b. Coccidioides spp. are usually found in wet climates
c. Up to 50 percent of people in endemic areas have been exposed to Coccidioides spores
d. Coccidioides spp. are found on the surface of the soil
C Up to 50 percent of people in endemic areas have been exposed to Coccidioides spores
Rationale: Coccidioidomycosis is a reemerging infectious disease caused by inhalation of airborne spores of the soil fungus Coccidioides immitis or C. posadasii. Coccidioides spp. are native to arid and desert areas in North America (California, Arizona, Texas, Utah, Nevada, New Mexico, and northern parts of Mexico), Central America, and South America. Coccidioides spp. are found in lower elevation areas that receive less than 20 inches of rain per year and have warm, sandy soil. They are usually found 4 to 12 inches below the surface. Among persons living in coccidioidomycosis-endemic areas, approximately 10 to 50 percent have been exposed to Coccidioides spp.
41. The IP wishes to know the proportion of a disease that could be prevented by eliminating the exposure in the entire study population. In order to determine this information, the IP will need to calculate the:
a. Attributable fraction
b. Attributable risk
c. Population attributable risk percent
d. Negative predictive value
C Population attributable risk percent
Rationale: Attributable risk percent (ARP) is a calculation that can be derived from the attributable risk, which is the difference in rate of a condition between an exposed population and an unexposed population. ARP gives the proportion of cases attributable (and avoidable) to this exposure in relation to all cases.
42. The precision of an estimate of a relative risk depends on which of the following:
a. Generalisability
b. Size of the study
c. Validity of the study
d. Presence of bias
B Size of the study
Rationale: The precision of the relative risk is related to the power of a study. Statistical power is affected chiefly y the size of the effect and the size of the sample used to detect it.
43. The most common reservoir for highly pathogenic avian influenza H5N1 virus is:
a. Migratory birds
b. Pigeons and doves
c. Water fowl
d. Domestic poultry
D Domestic poultry
Rationale: Highly pathogenic avian influenza A (H5N1) virus—referred to as HPAI H5N1 and sometimes shortened to H5N1—is a virus that occurs mainly in birds, especially domestic poultry. H5N1 is highly contagious among birds and can be deadly to them. Though relatively rare, sporadic human infections with this virus have occurred and have caused serious illness and death.
44. Indirect and direct causes of disease may form a complex network of events that determines the level of disease in a community. Which of the following is the term for this interrelation of events?
a. Applied epidemiology
b. Iceberg phenomenon
c. Causal web
d. Dendrogram
C Causal web
Rationale: Causation is an essential concept in epidemiology. The web of causation refers to the interrelationship of multiple factors that contribute to the occurrence of a disease.
45. Which of the following statements is true when the prevalence of a disease is very low?
a. The sensitivity of a diagnostic test is greatly increased
b. The specificity of a diagnostic test is much greater
c. The negative predictive value of a diagnostic test is very low
d. The positive predictive value of a diagnostic test is lowered
D The positive predictive value of a diagnostic test is lowered
Rationale: The measures of sensitivity and specificity describe hw well the proposed screening test performs against a "gold standard" test. Sensitivity and specificity ae independent of prevalence of disease. The positive predictive value (PPV) describes the probability of having the disease given a positive screening test result in the screened population. The negative predictive value (NPV) describes the probability of not having the disease given a negative screening test result in the screened population. PPV and NPV are disease prevalence dependent. Generally a higher prevalence will increase the PPV and decrease the NPV.
46. On July 7, a 30-year-old male is admitted to the medical ICU with a 2-day history of acute gastroenteritis symptoms. The IP suspects the patient is infected with norovirus. Which of the following statements regarding the epidemiology of norovirus infection supports this?
a. Most norovirus outbreaks are caused by genotype GII.2
b. Severe cases of norovirus are most common in adults aged 25 to 45
c. Noroviruses are the most common cause of epidemic gastroenteritis worldwide
d. Norovirus outbreaks occur most commonly in the summer months
C Noroviruses are the most common cause of epidemic gastroenteritis worldwide
Rationale: Noroviruses (NoVs) are the most common cause of epidemic gastroenteritis worldwide and the leading cause of foodborne outbreaks in the United States. Severe disease associated with NoV occurs most frequently among older adults, young children, and immunocompromised patients. NoV outbreaks occur year round, but activity increases in the United States during the winter months; 80 percent of reported outbreaks occur during November- April. Most NoV outbreaks are attributed to genotype GII.4, which evolves rapidly over time.
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48. A 40-year-old female is admitted with a 3-day history of diarrhea and fever. She is placed in Contact Isolation for a suspected Clostridium difficil infection (CDI). The patient also reports that she has had increasing abdominal pain for the past year, and inflammatory bowel disease (IBD) is in the list of potential diagnoses. Which of the following statements is most accurate regarding the relationship between IBD and CDI?
a. IBD is associated with increased morbidity and mortality associated with CDI
b. Most patients with IBD acquire CDI in inpatient settings
c. CDI generally develops more slowly after hospital admission among patients with IBD compared with patients without IBD
d. IBD does not affect the risk of CDI from antibiotic exposure
A IBD is associated with increased morbidity and mortality associated with CDI
Rationale: As CDI has become more common, CDI in individuals with IBD has become a focus of increased attention. IBD has been identified as antindependent risk factor for C. difficil colonization and disease; patients with IBD have increased severity of illness and higher death rates from CDI.
49. Which of the following statements about TB and airborne diseases among homeless individuals is most accurate?
a. Most TB infections among homeless individuals are reactivations of established disease
b. Sputum testing detects more than 90 percent of patients with TB
c. Screening for TB with chest X-ray may be the most cost- effective approach
d. Directly observed therapy in the acute hospital setting is associated with the highest completion rates
C Screening for TB with chest X-ray may be the most cost-effective approach
Rationale: TB incidence is higher in homeless populations than in the general population. Molecular epidemiology studies indicate that most TB cases occurring in the homeless are primary infections. The spread of TB among the homeless is related to recent person-to-person transmission, which produces outbreaks with large clusters in which more than 50 percent of persons are infected. Homeless shelters are major sites of transmission. Screening by chest radiography either periodically in all residents or specifically in symptomatic persons (e.g., chronic coughers) appears to be the most cost-effective approach for TB detection and diagnosis in this population.
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