Order Description
It is an epidemiology assignment which about calculation questions and critical thinking.
QUESTION 1
1. BACKGROUND TO THIS ASSIGNMENT:
Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. If left untreated or inadequately treated, syphilis can cause serious illness and eventually death. Untreated syphilis during pregnancy can result in significant morbidity (including the transmission of syphilis) or mortality of the unborn foetus or neonate.
Screening for syphilis in women in the early- and late-stages of pregnancy may significantly reduce the burden of syphilis to both the mother and child. The most common screening tests are based on serological tests for the detection of antibodies. The following table summarises the sensitivity and specificity of a number of potential screening tests for syphilis*. Please examine the data and answer Questions 1 to 4.
Test Sensitivity Specificity
VDRL 78% 98%
RPR card 86% 98%
USR 80% 99%
TP-PA 88% 96%
*Adapted from Ratnam 2005. Can J Infect Dis Med Microbial. 16(1):45-51
Question 1:
Based on the above information, which test would you select for screening if you were interested in ensuring that no cases of syphilis are missed?
a. VDRL, RPR card and USR are all roughly equivalent
b. RPR card
c. TP-PA
d. USR
e. VDRL
1 points
QUESTION 2
1. A questionnaire was administered to all pregnant women assessing their likihood of exposure to syphilis, based on a number of known risk factors. Health authorities decided to implement compulsory syphilis screening using the RPR-card test for all pregnant women who ticked ‘yes’ to 2 or more risk factors for syphilis. The prevalence of syphilis in the group of women selected for screening was 9%.
Calculate the positive predictive value (PPV) of the test in this group
(NOTES: express your answer as a percentage, however do NOT put the ‘%’ sign in your answer, simply the number;
While it is not realistic to have e.g. ‘0.6 of a person’, for the purposes of accuracy, keep all calculations unrounded until the final answer)
1 points
QUESTION 3
1. How would you interpret the PPV calculated in Q2? (1 sentence)
QUESTION 1
1. BACKGROUND TO THIS ASSIGNMENT:
Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. If left untreated or inadequately treated, syphilis can cause serious illness and eventually death. Untreated syphilis during pregnancy can result in significant morbidity (including the transmission of syphilis) or mortality of the unborn foetus or neonate.
Screening for syphilis in women in the early- and late-stages of pregnancy may significantly reduce the burden of syphilis to both the mother and child. The most common screening tests are based on serological tests for the detection of antibodies. The following table summarises the sensitivity and specificity of a number of potential screening tests for syphilis*. Please examine the data and answer Questions 1 to 4.
Test Sensitivity Specificity
VDRL 78% 98%
RPR card 86% 98%
USR 80% 99%
TP-PA 88% 96%
*Adapted from Ratnam 2005. Can J Infect Dis Med Microbial. 16(1):45-51
Question 1:
Based on the above information, which test would you select for screening if you were interested in ensuring that no cases of syphilis are missed?
a. VDRL, RPR card and USR are all roughly equivalent
b. RPR card
c. TP-PA
d. USR
e. VDRL
1 points
QUESTION 2
1. A questionnaire was administered to all pregnant women assessing their likihood of exposure to syphilis, based on a number of known risk factors. Health authorities decided to implement compulsory syphilis screening using the RPR-card test for all pregnant women who ticked ‘yes’ to 2 or more risk factors for syphilis. The prevalence of syphilis in the group of women selected for screening was 9%.
Calculate the positive predictive value (PPV) of the test in this group
(NOTES: express your answer as a percentage, however do NOT put the ‘%’ sign in your answer, simply the number;
While it is not realistic to have e.g. ‘0.6 of a person’, for the purposes of accuracy, keep all calculations unrounded until the final answer)
1 points
QUESTION 3
1. How would you interpret the PPV calculated in Q2? (1 sentence)
QUESTION 4
1. There was some concern amongst clinicians that compulsory screening only for women with 2 or more risk factors for syphilis (in Q2) may miss cases in women who do not identify as having several risk factors. It was therefore suggested that the syphilis screening test be made compulsory for all pregnant women (prevalence of syphilis = 0.5%).
Comment on how the decision to screen all pregnant women will impact on the performance of the RPR-card screening test. (Note: in order to receive full marks you will need to support your answer with appropriate epidemiological measures/calculations)
3 points
QUESTION 5
1. A number of factors (e.g. age, pregnancy, comorbidities such as leprosy, systemic lupus erythematosus, thyroiditis etc.) are known to impact the likelihood of false-positive test results for the syphilis screening test. These factors are therefore likely to impact: (select all that apply)
a. Negative predictive value of the screening test
b. Sensitivity of the screening test
c. Prevalence of syphilis in the screened population
d. Positive predictive value of the screening test
e. Specificity of the screening test
1 points
QUESTION 6
1. Thinking more generally about the purpose of syphilis screening (leading to effective treatment) from both the perspective of the mother and also the developing foetus, complete the following sentence using options from the drop down menu:
In terms of syphilis infection, screening (and effective treatment) for syphilis during pregnancy is a form of prevention for the mother and a form of prevention for the foetus/baby.
1 points
QUESTION 7
1. QUESTIONS 7 to 12 refer to the study by Hawkes et al., 2011:Effectiveness of interventions to improve screening for syphilis in pregnancy: a systematic review and meta-analysis (provided with this assignment).
Question 7:
Figure 4B of the study by Hawkes et al., 2011 depicts a forest plot illustrating the estimates of the association between an intervention and risk of perinatal death. In Figure 4B, how many studies reported statistically significant reductions in perinatal deaths in the intervention group compared to the control group? (Note: for the purposes of this question, consider each individual estimate as a separate study) (please write the number only)
1 points
QUESTION 8
1. How would you interpret the summary (pooled) estimate in Figure 4B? (1 sentence)
1 points
QUESTION 9
1. This systematic review included 10 studies, however only 4 studies were included in the meta-analysis. Why is this? (1-2 sentences)
1 points
QUESTION 10
1. In the second paragraph of results the authors state that “two studies were cluster randomized trials (from Mongolia and South Africa; table 1). A risk of bias existed in both because the assessment of outcomes was not reported to have been blinded”.
Which tool might the authors have used to guide the risk of bias assessment for these studies?
a. MOOSE guidelines
b. The Newcastle-Ottawa Scale
c. JADAD Scale
d. CONSORT guidelines
e. PRISMA guidelines
1 points
QUESTION 11
1. In the second paragraph of the results the authors state that “A risk of bias existed in all non-randomised studies (table 3); no study with parallel groups controlled for differences between intervention and control clinics”. What epidemiological phenomenon is this statement referring to?
1 points
QUESTION 12
1. Publication bias is a common source of bias in systematic reviews. If studies finding no impact of an antenatal screening intervention on adverse pregnancy outcomes were less likely to be published, what would the likely impact be on the findings of the meta-analysis?
a. There would be no association between the exposure and the outcome
b. No impact on the magnitude of the association between the exposure and the outcome
c. An over-estimation of the association between the exposure and the outcome
d. An under-estimation of the association between the exposure and the outcome
e. The association between the exposure and the outcome would be confounded
1 points
QUESTION 13
1. In the year 2020, a vaccine is developed that provides immunity against developing syphilis, if vaccinated. If this was made available, this would be considered what level of prevention?
a. Secondary
b. Community
c. High-risk
d. Tertiary
e. Primary
1 points
QUESTION 14
1. An epidemiologist wants to ensure the vaccination is effective in those currently free of syphilis and therefore decides to conduct a randomised control trial. She wants to ensure that only participants who are currently free of syphilis are enrolled in her trial. Therefore she screens a large group of potential participants using a screening test. Based on the outcome of this test, she decides who is eligible to participate (free of disease) in the vaccination trial. For this purpose, it is very important that the diagnostic test has a high ________?
a. All of the above
b. Positive Predictive Value
c. Specificity
d. Sensitivity
e. Negative Predictive Value
1 points
QUESTION 15
1. The Government of a Developing Nation is concerned about the burden of syphilis during pregnancy in their country. In order to reduce the burden of syphilis in pregnant women, the Government wishes to introduce the new vaccine to all women of childbearing age. Unfortunately, there is limited funding available and the Government therefore needs to prioritise vaccination to a specific at-risk group of women that will make the biggest impact on reducing the public health burden of syphilis.
A public health policy official, John, identifies a case-control study that had previously been conducted in their country, which examined risk factors for syphilis infection in women. Data from the study is found in the Table below. As the government epidemiologist, John comes to see you to ask for advice on how to interpret the data and prioritise which at-risk group of women should get the vaccination.
Based on the data provided below, prioritise the at-risk groups in order of which the vaccination would make the biggest impact on the public health burden of syphilis in your country (where 1 is the at-risk group with the biggest impact, an 3 is the at-risk group with the smallest impact).
(Note: for full marks in your answer, please provide: 1. The order of how you would prioritise the at-risk groups for vaccination, and 2. the relevant calculations/epidemiological measures that you used to inform your decision. Also note, for the purposes of this exercise assume that all risk factors act independently of one another when thinking about at-risk groups.)
Risk Factor Number of Controls with risk factor OR (syphilis)
History of previous STI 6 13.90
2 or more previous sexual partners in past 5 years 123 3.80
Marital Status (Single) 21 4.16
Total Controls = 357
Note: Controls may have more than one risk factor
STI = sexually transmitted infection
4 points
QUESTION 16
1. Complete the following sentence from the drop-down menu options:
In terms of causation, exposure to T pallidum (the syphilis bacteria) is a cause, and engaging in risky sexual behaviour is considered a cause.
1 points
QUESTION 17
1. Based on your decision from Question 15, the Government implements the syphilis vaccine program in the prioritised at-risk group. As the government epidemiologist, you decide to set up a pre-post implementation study to examine changes in your at-risk population. Which epidemiological measure do you select to be your primary measure to assess the effectiveness of this intervention?
a. Incidence rate of syphilis
b. the prevalence of women in the at-risk group
c. prevalence of syphilis
d. odds ratio between the risk factor and syphilis
e. mortality rate of syphilis
1 points
QUESTION 18
1. Based on the success of your vaccination program in the at-risk group, the Government decides to invest more money into administering the vaccination to more of the community. If syphilis has a reproductive number of 2.5, what proportion of the population would you need to vaccinate to achieve the herd immunity threshold?
a. 97.5%
b. 60%
c. 40%
d. 25%
e. 75%
1 points
QUESTION 19
1. The Government decides that it is necessary to continue monitoring the rates of syphilis in pregnant women. They randomly select a number of antenatal clinics from across the country and set up syphilis testing facilities, which report any positive test results back to the government epidemiologist. This type of surveillance is best known as:
a. Syndromic surveillance
b. Passive surveillance
c. Event-based surveillance
d. Sentinel surveillance
e. Process surveillance
1 points
QUESTION 20
1. Complete the following statement:
The attributable burden of a disease due to a given risk factor is:
a. Always smaller than the burden due to other risk factors
b. Unpredictable
c. Always larger than the burden due to other risk factors
d. Unavoidable
e. Avoidable
