Epidemiology — MCQs

A rheumatologist is interested in studying the association between osteoporosis and the risk of sustaining a distal radius fracture. To explore this association, she develops a retrospective study design in which she identifies patients in a large institutional database over the age of 55 with and without osteoporosis, then follows them over a 10-year period to identify cases of distal radius fracture. She matches patients on age, sex, and body mass index to control for known confounding. After completing the study, she finds that patients with osteoporosis were at an increased risk of developing distal radius fractures. Which of the following study designs did this investigator use in this case?

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1561: Which of the following is a true statement about screening tests for genetic diseases?

A. Screening test has better accuracy than diagnostic test
B. It is always invasive
C. It defines risk of transmission of disease to the child (Correct Answer)
D. Screening requires genetic mapping

Explanation: ***Correct: It defines risk of transmission of disease to the child*** - Genetic screening aims to identify individuals or couples at risk of passing on **heritable genetic conditions** to their offspring. - This information helps in **family planning** and provides prenatal diagnostic options if the risk is high. - This is the **primary purpose** of genetic screening programs. *Incorrect: Screening test has better accuracy than diagnostic test* - **Screening tests** are designed to be broad and detect potential risks, often with lower specificity and sensitivity than diagnostic tests. - **Diagnostic tests** are typically more accurate and definitive, confirming the presence or absence of a disease after a positive screening result. *Incorrect: It is always invasive* - Many genetic screening tests, such as **non-invasive prenatal screening (NIPS)** from maternal blood or carrier screening via saliva, are non-invasive or minimally invasive. - While some diagnostic tests like **amniocentesis** or **chorionic villus sampling** are invasive, screening itself is not universally so. *Incorrect: Screening requires genetic mapping* - **Genetic mapping** refers to determining the relative positions of genes on a chromosome, which is a research tool for understanding genome organization. - Genetic screening primarily involves testing for specific mutations or chromosomal abnormalities, not creating a comprehensive genetic map of an individual.

Question 1562: Match the incubation periods of the following diseases: a. Syphilis b. SARS c. Hepatitis A d. Chickenpox Match with: 1. 10-21 days 2. 21 days (3 weeks) 3. 2-7 days 4. 15-50 days

A. a-2, b-3, c-4, d-1 (Correct Answer)
B. a-3, b-4, c-2, d-1
C. a-2, b-3, c-1, d-4
D. a-4, b-3, c-1, d-2

Explanation: ***a-2, b-3, c-4, d-1*** - This option correctly matches all incubation periods: **Syphilis (a) = 21 days (3 weeks)** - the average incubation for primary chancre appearance is 21 days (range 10-90 days). - **SARS (b) = 2-7 days** - the typical incubation period for SARS-CoV-1 is 2-10 days, with most cases manifesting within 2-7 days. - **Hepatitis A (c) = 15-50 days** - the standard incubation period averages 28-30 days (range 15-50 days). - **Chickenpox (d) = 10-21 days** - varicella has a well-established incubation of 10-21 days, typically 14-16 days. *a-3, b-4, c-2, d-1* - This incorrectly assigns **2-7 days to Syphilis**, which is far too short for the primary chancre to appear (actual: 21 days average). - **15-50 days for SARS** is excessively long; SARS manifests within 2-10 days. - **21 days for Hepatitis A** is at the lower end but not representative of the typical range (15-50 days). *a-2, b-3, c-1, d-4* - This incorrectly pairs **10-21 days with Hepatitis A**, which has a longer incubation (15-50 days). - **15-50 days for Chickenpox** is too long; varicella's incubation is 10-21 days. *a-4, b-3, c-1, d-2* - This incorrectly assigns **15-50 days to Syphilis** (actual: 21 days average) and **10-21 days to Hepatitis A** (actual: 15-50 days). - While these ranges have some overlap with actual values, they represent inversions of the correct assignments.

Question 1563: Which of the following statements are true? 1. Due to increasing mammography there occurs over diagnosis of breast carcinoma 2. Colon cancer screening is done by digital rectal examination 3. Oral cancer screening is done by visual inspection 4. Cervix cancer screening is done by a pap smear

A. 1,2,3,4
B. 4 only
C. 1,3,4 (Correct Answer)
D. 2,3,4

Explanation: ***Correct: 1,3,4*** - **Statement 1 is TRUE**: Overdiagnosis is a well-documented consequence of increased mammography screening. It detects slow-growing tumors that might never have caused clinical symptoms or harm during a woman's lifetime, leading to unnecessary treatment and associated morbidities. - **Statement 3 is TRUE**: Oral cancer screening primarily involves thorough visual inspection by a healthcare professional to identify suspicious lesions, ulcers, or color changes in the oral cavity. - **Statement 4 is TRUE**: Cervical cancer screening is effectively done by Pap smear, which detects precancerous and cancerous cells. - **Statement 2 is FALSE**: Digital rectal examination is NOT the primary screening method for colon cancer. Standard screening methods include colonoscopy, fecal occult blood testing (FOBT), and fecal immunochemical test (FIT). *Incorrect: 1,2,3,4* - While statements 1, 3, and 4 are true, statement 2 is incorrect. Digital rectal examination is not a primary or definitive screening method for colon cancer—it only examines the rectum and misses most of the colon. *Incorrect: 4 only* - While cervical cancer screening by Pap smear is true, this option is incomplete as it misses other true statements (1 and 3) regarding mammography overdiagnosis and oral cancer screening. *Incorrect: 2,3,4* - This option incorrectly includes statement 2. Colon cancer screening is NOT done by digital rectal examination. Proper screening methods include colonoscopy, FOBT, FIT, and flexible sigmoidoscopy.

Question 1564: A new drug has been introduced into the market which was found to decrease mortality but it does not cure the disease. Which of the following is a true statement regarding prevalence and incidence?

A. Increase in prevalence (Correct Answer)
B. Decrease in incidence
C. Decrease in prevalence
D. Increase in incidence

Explanation: ***Increase in prevalence*** - A drug that decreases mortality without curing the disease means people **live longer with the condition**, thus increasing the duration of disease - **Prevalence = Incidence × Duration**: Since duration increases while incidence remains constant, prevalence increases - More existing cases accumulate over time as fewer patients die from the disease *Decrease in incidence* - **Incidence** refers to the rate at which **new cases** develop in a population - This drug affects survival of existing cases, not the development of new cases - Since the drug neither prevents nor promotes new cases, **incidence remains unchanged** (not decreased) *Decrease in prevalence* - Prevalence would decrease if the drug **cured the disease** (removing people from the diseased pool) or if **mortality increased** - The scenario describes the opposite: decreased mortality without cure, which **increases** prevalence *Increase in incidence* - This would mean more new cases are developing over time - The drug affects **survival** of existing cases, not the **rate of new diagnoses** - Incidence remains unchanged, not increased

Question 1565: Which of the following is not a part of case-control studies?

A. Strength of association
B. Follow up (Correct Answer)
C. Matching
D. Selection of study subjects

Explanation: ***Follow up*** - **Follow-up** of participants over time to observe disease incidence or outcomes is a characteristic of **cohort studies**, not case-control studies. - Case-control studies are typically **retrospective**, looking back in time after disease occurrence. *Strength of association* - Measuring the **strength of association** between an exposure and an outcome using metrics like the **odds ratio** is a primary objective of case-control studies. - This helps quantify the increased risk of disease attributable to a particular exposure. *Matching* - **Matching** is a technique frequently used in case-control studies to control for **confounding variables** by selecting controls who are similar to cases in terms of age, gender, or other relevant factors. - This helps ensure that any observed association is truly due to the exposure and not other differences between the groups. *Selection of study subjects* - The **selection of study subjects** is fundamental in case-control studies, involving the identification of individuals with the disease (**cases**) and a comparable group without the disease (**controls**). - Careful selection is crucial to minimize bias and ensure the validity of the study findings.

Question 1566: Which indicator best measures the effectiveness of an STI control program's prevention efforts?

A. Number of screenings performed
B. Treatment completion rates
C. Incidence of new infections (Correct Answer)
D. Number of cases treated

Explanation: ***Incidence of new infections*** - A decrease in the **incidence of new infections** directly reflects the success of **prevention strategies** in reducing overall disease transmission. - This indicator assesses the program's ability to prevent people from acquiring STIs, which is the ultimate goal of prevention efforts. *Number of screenings performed* - The number of screenings performed measures **program activity** and **reach**, but not necessarily the effectiveness of prevention. - While screening is crucial for early detection and treatment, it doesn't directly indicate a reduction in the **rate of new transmissions**. *Treatment completion rates* - Treatment completion rates are important for individual patient outcomes and reducing further transmission from **infected individuals**. - However, they primarily reflect the **effectiveness of treatment delivery** rather than the success of primary prevention among the uninfected population. *Number of cases treated* - The number of cases treated indicates the **burden of disease** and the program's response to it, but doesn't directly measure prevention success. - This metric can increase even if prevention efforts are failing, due to a rise in new infections or improved case finding.

Question 1567: Which component of the National STI Control Program is most effective at directly interrupting the transmission chain of gonorrhea?

A. Antibiotic resistance monitoring
B. Health education campaigns
C. Partner notification services (Correct Answer)
D. Mass screening programs

Explanation: ***Partner notification services*** - **Partner notification** directly targets the transmission chain by systematically identifying and treating exposed individuals, thereby interrupting further spread at the source. - This intervention is uniquely positioned to break the cycle of infection by ensuring that **asymptomatic or unaware partners** receive timely diagnosis and treatment, preventing onward transmission. - Studies show that partner notification services have high yields in identifying undiagnosed cases and preventing secondary transmission. *Antibiotic resistance monitoring* - While crucial for guiding treatment strategies and ensuring therapeutic efficacy, **antibiotic resistance monitoring** does not directly interrupt transmission chains. - Its impact is **indirect**, preventing treatment failures that could lead to prolonged infectiousness and continued transmission. *Health education campaigns* - **Health education campaigns** aim to increase awareness and promote safer sexual practices, contributing to primary prevention. - However, their impact on *interrupting existing transmission chains* is indirect and requires behavioral change over time, making them less immediately effective than direct contact tracing. *Mass screening programs* - **Mass screening programs** can identify infected individuals in populations, but their effectiveness depends on coverage, uptake, and linkage to treatment. - Without robust **partner notification and follow-up services**, screening alone may miss the contacts who perpetuate transmission chains.

Question 1568: A district reports increasing syphilis cases despite standard interventions. Which program response is most appropriate?

A. Mass treatment campaign
B. Enhanced surveillance with targeted outreach and screening (Correct Answer)
C. Increasing clinic hours only
D. Public awareness campaign only

Explanation: ***Enhanced surveillance with targeted outreach and screening*** - This approach specifically addresses the rise in cases by actively finding and treating infected individuals and their contacts, which is crucial for **controlling outbreaks** of sexually transmitted infections like **syphilis**. - **Targeted outreach** ensures high-risk populations are reached, and **enhanced surveillance** allows for better understanding of transmission patterns to guide interventions. *Mass treatment campaign* - **Mass treatment** campaigns are generally reserved for diseases with high prevalence and potential for rapid spread in a community, and are typically not the first response for **syphilis**, which often requires individual diagnosis and partner notification. - While it might reduce prevalence, it doesn't address ongoing transmission dynamics or identify specific **risk factors** at an individual level. *Increasing clinic hours only* - While increased clinic access is beneficial, it is a passive approach that does not actively identify cases or reach individuals who may not seek care, especially those who are **asymptomatic** or face barriers to accessing healthcare. - It might improve access for those already motivated to seek care but won't effectively address an increasing trend in cases by itself. *Public awareness campaign only* - A public awareness campaign can improve knowledge but does not directly lead to diagnosis and treatment, which are essential for controlling an active increase in syphilis cases. - It's a supportive measure but insufficient as a primary response to an **epidemic trend** without accompanying diagnostic and therapeutic services.

Question 1569: Why is sentinel surveillance preferred over passive surveillance in STI control programs?

A. Eliminates reporting bias
B. Covers larger population
C. Provides more detailed and accurate data from selected sites (Correct Answer)
D. Requires less resources

Explanation: ***Provides more detailed and accurate data from selected sites*** - **Sentinel surveillance** involves selected, well-defined sites that actively collect high-quality, detailed data, providing a more accurate picture of STI trends and characteristics. - This focused data collection allows for better understanding of specific risk factors and population subgroups, which is crucial for targeted interventions. *Eliminates reporting bias* - While sentinel surveillance aims to **reduce reporting bias** through systematic, active data collection, it does not entirely eliminate it, as some biases related to site selection or specific patient populations may still exist. - No surveillance system is completely free of bias, but sentinel systems are designed to minimize it compared to passive systems. *Covers larger population* - **Passive surveillance**, by virtue of collecting data from all healthcare providers, theoretically covers a larger, more general population. - Sentinel surveillance focuses on specific sites or populations, providing in-depth data rather than broad population coverage. *Requires less resources* - **Sentinel surveillance** typically requires more resources per case, as it involves active data collection, specialized training, and potentially enhanced laboratory testing at selected sites. - **Passive surveillance** often requires fewer designated resources for active data collection since reporting is voluntary and relies on existing healthcare infrastructure.

Question 1570: A rheumatologist is interested in studying the association between osteoporosis and the risk of sustaining a distal radius fracture. To explore this association, she develops a retrospective study design in which she identifies patients in a large institutional database over the age of 55 with and without osteoporosis, then follows them over a 10-year period to identify cases of distal radius fracture. She matches patients on age, sex, and body mass index to control for known confounding. After completing the study, she finds that patients with osteoporosis were at an increased risk of developing distal radius fractures. Which of the following study designs did this investigator use in this case?

A. Case-control study
B. Cross-sectional study
C. Cohort study (Correct Answer)
D. Ecological study

Explanation: ***Cohort study*** - This study design **identifies groups based on exposure status** (with or without osteoporosis) and **follows them forward in time** to observe the development of an outcome (distal radius fracture). - The investigator collected data on exposure first, then observed outcomes over a 10-year period, which is characteristic of a **prospective** or **retrospective cohort study**. *Case-control study* - This design **starts with identifying individuals with the outcome (cases)** and a comparison group without the outcome (controls), then **looks backward in time** to determine past exposures. - The study described here starts with exposure status (osteoporosis) first, not the outcome (fracture). *Cross-sectional study* - This study assesses **exposure and outcome simultaneously at a single point in time**, providing a "snapshot" of the prevalence of both. - The rheumatologist in this scenario followed patients over a 10-year period, indicating a longitudinal design, not a single point in time. *Ecological study* - This type of study **analyzes data at a population level**, rather than at the individual level, to find correlations between exposure and outcome. - The study described explicitly involves identifying and following **individual patients**, not groups or populations.

Practice by Chapter

Principles of Epidemiology

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Measures of Disease Frequency

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Epidemiological Study Designs

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Descriptive Epidemiology

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Analytical Epidemiology

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Experimental Epidemiology

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Screening for Disease

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Surveillance Systems

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Investigation of an Epidemic

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Association and Causation

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Modern Epidemiological Methods

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Critical Appraisal of Epidemiological Studies

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