Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1681: In an international health survey, which statistical measure is most appropriate for comparing the prevalence of HIV among different countries?

A. Relative risk
B. Prevalence ratio (Correct Answer)
C. Incidence rate
D. Mortality rate

Explanation: ***Prevalence ratio*** - When comparing HIV prevalence across different countries, we need a measure that allows **direct comparison of disease burden**. - While **standardized prevalence rates** (per 100,000 population) are the standard epidemiological measure for international comparisons, a **prevalence ratio** can be used to express how many times more prevalent HIV is in one country compared to another (e.g., Country A has 2× the prevalence of Country B). - Among the given options, this is the most appropriate for comparing existing disease burden across populations. *Relative risk* - **Relative risk** (risk ratio) compares the **incidence** (new cases) of disease between exposed and unexposed groups in cohort studies. - It measures the **risk of developing** a disease, not the existing burden of disease (prevalence), making it unsuitable for this question. - Used primarily in analytical epidemiology, not descriptive international comparisons. *Incidence rate* - **Incidence rate** measures the rate at which **new HIV infections** occur in a population over a specified time period. - While useful for understanding disease transmission dynamics, it does **not measure the total burden** of people living with HIV (prevalence) at a given point in time. - Prevalence includes both new and existing cases, providing a better picture of disease burden for health planning. *Mortality rate* - **Mortality rate** measures the frequency of **deaths** due to a specific cause in a population over a given period. - For HIV, this reflects treatment availability and disease severity, but does **not indicate the number of people living with HIV**, which is what prevalence measures. - With modern antiretroviral therapy, HIV mortality has decreased significantly while prevalence remains high.

Question 1682: What is the aim of the Integrated Disease Surveillance Project (IDSP)?

A. A systematic approach to detect and respond to communicable and non-communicable diseases (Correct Answer)
B. An insurance scheme for chronic illnesses
C. A database for genetic diseases
D. A research platform for developing new drugs

Explanation: ***A systematic approach to detect and respond to communicable and non-communicable diseases*** - The IDSP was launched to establish a **decentralized, state-based surveillance system** for epidemic-prone diseases. - Its core objective is to detect and respond to outbreaks of diseases early, thereby minimizing morbidity and mortality. *An insurance scheme for chronic illnesses* - This option describes a **health insurance program**, which is distinct from a disease surveillance system. - **IDSP focuses on tracking and controlling disease spread**, not on financing healthcare for chronic conditions. *A database for genetic diseases* - While IDSP collects health data, its primary focus is on **infectious and non-communicable disease trends and outbreaks**, not solely on genetic diseases. - Databases for genetic diseases would involve different data types and objectives. *A research platform for developing new drugs* - **IDSP's role is surveillance and early warning**, not drug discovery or development. - Drug development is a complex process typically managed by pharmaceutical companies and research institutions.

Question 1683: A public health researcher is comparing the effectiveness of two vaccines using a cohort study. After calculating the relative risk, the researcher finds an RR of 0.5 for Vaccine A compared to Vaccine B. What does this result indicate about Vaccine A?

A. Vaccine A reduces the risk of disease by 50% compared to Vaccine B. (Correct Answer)
B. Vaccine A increases the risk of disease by 50% compared to Vaccine B.
C. Vaccine A has no effect on disease risk compared to Vaccine B.
D. Vaccine A and Vaccine B are equally effective.

Explanation: ***Vaccine A reduces the risk of disease by 50% compared to Vaccine B.*** - A **relative risk (RR)** of 0.5 means that the risk of disease in the group exposed to Vaccine A is **half** that of the group exposed to Vaccine B. - This translates to a **50% reduction in risk** (1 - 0.5 = 0.5, or 50% reduction), indicating that Vaccine A is more effective in preventing the disease. *Vaccine A increases the risk of disease by 50% compared to Vaccine B.* - An RR greater than 1 would indicate an **increased risk** of disease. For example, an RR of 1.5 would suggest a 50% increased risk. - Since the calculated RR is 0.5, it represents a protective effect, not an increase in risk. *Vaccine A has no effect on disease risk compared to Vaccine B.* - An RR of **1.0** indicates no difference in risk between the two groups, meaning no effect. - An RR of 0.5 clearly demonstrates a difference in risk, specifically a reduction. *Vaccine A and Vaccine B are equally effective.* - Equal effectiveness would be observed if the **relative risk was 1.0**, indicating identical risk ratios between the two vaccines. - An RR of 0.5 suggests that Vaccine A is **more effective** than Vaccine B in reducing the risk of disease.

Question 1684: In a cohort study, the relative risk (RR) of developing lung cancer in smokers compared to non-smokers is 5. What does this indicate?

A. Smokers are five times more likely to develop lung cancer compared to non-smokers. (Correct Answer)
B. Lung cancer is five times more common in the general population.
C. There is a 5% chance of developing lung cancer in smokers.
D. A fixed proportion of smokers will develop lung cancer.

Explanation: ***Smokers are five times more likely to develop lung cancer compared to non-smokers.*** - A **relative risk (RR)** of 5 indicates that the **incidence** of lung cancer in the exposed group (smokers) is 5 times higher than in the unexposed group (non-smokers). - This directly quantifies how much more likely an outcome is in one group compared to another, adjusted for **baseline risk**. *Lung cancer is five times more common in the general population.* - This statement refers to the **prevalence** or **overall incidence** in the general population, which is not directly indicated by a relative risk comparing two specific groups. - The relative risk specifically compares the exposed group to the unexposed group, not the overall population. *There is a 5% chance of developing lung cancer in smokers.* - The relative risk of 5 means the *ratio* of risk is 5, not that the *absolute risk* or probability for smokers is 5%. - To determine the absolute chance, one would need to know the baseline risk in non-smokers. *A fixed proportion of smokers will develop lung cancer.* - While it's true some smokers will develop lung cancer, a relative risk value of 5 does not define a "fixed proportion" in absolute terms. - It only states that the risk among smokers is 5 times greater than among non-smokers, not what percentage this translates to for either group.

Question 1685: Which of the following is included in the Integrated Disease Surveillance Programme (IDSP)?

A. All are included (Correct Answer)
B. Surveillance of communicable diseases
C. Surveillance of non-communicable diseases
D. Collection of environmental data

Explanation: ***All are included*** - The **Integrated Disease Surveillance Programme (IDSP)**, launched in 2004, has significantly **evolved and expanded** its scope over the years. - Currently, IDSP covers **surveillance of communicable diseases** (epidemic-prone diseases like cholera, dengue, malaria, measles, tuberculosis, COVID-19). - The programme now also includes **surveillance of non-communicable diseases** such as diabetes, hypertension, cardiovascular diseases, and cancer as part of India's comprehensive health surveillance strategy. - **Environmental surveillance** is integrated into IDSP for monitoring climate-sensitive diseases, vector-borne disease patterns, water quality in outbreak contexts, and environmental factors influencing disease transmission. - IDSP operates through a **decentralized, state-based surveillance system** with laboratory networks and IT-enabled reporting mechanisms under the Integrated Health Information Platform (IHIP). *Surveillance of communicable diseases* - While this is correct and remains the **core focus** of IDSP since its inception, it is **not the only component**. - This option is incomplete as it excludes the expanded mandate of the programme. *Surveillance of non-communicable diseases* - This is now **included in IDSP** as the programme has evolved beyond its original communicable disease focus. - However, this alone does not represent the complete scope of IDSP. *Collection of environmental data* - Environmental surveillance **is part of IDSP** for monitoring factors affecting disease patterns, particularly for climate-sensitive and vector-borne diseases. - This includes monitoring environmental determinants of health and disease outbreaks.

Question 1686: In a case-control study investigating the link between smoking and lung cancer, which measure of association is the most appropriate?

A. Relative risk
B. Attributable risk
C. Odds ratio (Correct Answer)
D. Incidence rate

Explanation: ***Odds ratio*** - The **odds ratio** is the most appropriate measure of association for **case-control studies** because these studies select participants based on disease status, making direct calculation of incidence or relative risk impossible. - It approximates the **relative risk** when the disease is rare, providing a valid estimate of the association between the exposure (smoking) and the outcome (lung cancer). *Relative risk* - **Relative risk** is calculated in **cohort studies** where participants are followed over time to observe the incidence of disease in exposed versus unexposed groups. - It cannot be directly calculated in a **case-control study** because the study design ascertains cases and controls based on outcome, not exposure status. *Attributable risk* - **Attributable risk**, also known as risk difference, measures the absolute excess risk of disease in the exposed group compared to the unexposed group. - Like relative risk, it is primarily used in **cohort studies** to determine the benefit of removing an exposure, and it requires incidence data. *Incidence rate* - **Incidence rate** measures the frequency with which new cases of disease occur in a population at risk over a specified period. - It is a measure reported in **cohort studies** or surveillance studies, not typically in case-control studies, which are designed to compare exposures between cases and controls.

Question 1687: Which of the following factors should be critically evaluated before introducing a new vaccine for tuberculosis in a high-burden country?

A. Prevalence of tuberculosis and political stability in the region.
B. Cost-effectiveness and cultural acceptance of the vaccine.
C. Efficacy of the vaccine and availability of healthcare infrastructure. (Correct Answer)
D. None of the options.

Explanation: ***Correct Option: Efficacy of the vaccine and availability of healthcare infrastructure*** When introducing a new vaccine in a high-burden country, the **most critical factors** to evaluate are: - **Vaccine efficacy**: This is the PRIMARY consideration - the vaccine must have proven effectiveness against tuberculosis in clinical trials. Without demonstrated efficacy, introduction cannot be justified regardless of other factors. - **Healthcare infrastructure availability**: Essential for successful vaccine delivery, including cold chain facilities, trained personnel, distribution networks, surveillance systems, and post-introduction monitoring. In high-burden countries, infrastructure assessment is critical as it determines feasibility of implementation. *Incorrect Option: Prevalence of tuberculosis and political stability in the region* - While **disease burden** (prevalence, incidence, mortality) is important for prioritization, it is typically already established in a "high-burden country" context as stated in the question. - **Political stability** is a contextual factor that affects implementation but is NOT among the primary scientific and technical evaluation criteria for vaccine introduction decisions according to WHO frameworks. *Incorrect Option: Cost-effectiveness and cultural acceptance of the vaccine* - **Cost-effectiveness** is important for sustainability and resource allocation but is typically evaluated AFTER efficacy is established. - **Cultural acceptance** impacts uptake but can be addressed through community engagement and health education programs; it's not a primary evaluation criterion for introduction decisions. *Incorrect Option: None of the options* - This is incorrect because Option C correctly identifies the two most critical evaluation factors according to standard vaccine introduction frameworks.

Question 1688: Which of the following is a characteristic of a cross-sectional study?

A. Measures prevalence of a disease. (Correct Answer)
B. Establishes a causal relationship.
C. Follows participants over time.
D. Used to measure incidence of a disease.

Explanation: ***Measures prevalence of a disease.*** - Cross-sectional studies collect data on both **exposure** and **outcome** at a single point in time, allowing for the calculation of disease **prevalence**. - They provide a **snapshot** of the health status and characteristics of a population at a specific moment. *Establishes a causal relationship.* - Cross-sectional studies often suffer from **reverse causality** or **temporality issues**, making it difficult to determine whether the exposure preceded the outcome. - Due to the simultaneous measurement of exposure and outcome, one cannot definitively conclude a **cause-and-effect relationship**. *Follows participants over time.* - This characteristic is typical of **longitudinal studies**, such as cohort studies, which track individuals over a period to observe changes or outcomes. - Cross-sectional studies are conducted at **one specific time point** and do not involve follow-up periods. *Used to measure incidence of a disease.* - **Incidence** refers to the rate of new cases of a disease in a population over a specified period, requiring follow-up over time. - This measure is typically obtained from **cohort studies** or clinical trials, not from a single-point-in-time cross-sectional study.

Question 1689: During a mass screening program for diabetes, a new test with a sensitivity of 85% and specificity of 90% is used. If the test is applied to a population with a low prevalence of diabetes, what is the most likely outcome?

A. Increased false positive results due to low prevalence (Correct Answer)
B. Increased true positive results due to high sensitivity
C. Increased false negative results due to low prevalence
D. Equal false positive and false negative results

Explanation: ***Increased false positive results due to low prevalence*** - In a population with **low disease prevalence**, even a test with high specificity will yield a significant number of **false positives** because there are many healthy individuals who will test positive. - While sensitivity and specificity are intrinsic to the test, the **positive predictive value (PPV)**, which reflects the likelihood of actually having the disease when testing positive, decreases dramatically with lower disease prevalence. *Increased true positive results due to high sensitivity* - While **high sensitivity** does mean that a large proportion of truly diseased individuals will be correctly identified as positive, the absolute number of **true positives** will be low if the disease itself is rare in the population. - The number of true positives is also directly limited by the **prevalence** of the disease. *Increased false negative results due to low prevalence* - **False negative results** are primarily influenced by the test's **sensitivity**, not directly by prevalence. A test with 85% sensitivity will miss 15% of true cases, regardless of how common or rare the disease is. - Low prevalence means there are fewer actual cases to begin with, so the absolute number of false negatives might be low, but the *proportion* of missed cases among true positives remains related to sensitivity. *Equal false positive and false negative results* - It is highly unlikely for **false positive** and **false negative** rates to be equal, as they are determined by different test characteristics (**specificity** and **sensitivity**, respectively) which are independent. - The impact of prevalence primarily skews the balance between false positives and true positives, and false negatives and true negatives.

Question 1690: Why is scabies frequently associated with outbreaks in institutional settings?

A. Direct skin-to-skin contact is common (Correct Answer)
B. It spreads via airborne droplets
C. The mites survive longer on surfaces
D. It is transmitted through contaminated food

Explanation: ***Direct skin-to-skin contact is common*** - **Scabies** is primarily transmitted through **prolonged direct skin-to-skin contact**, which is unavoidable in close-quarter institutional settings like nursing homes, hospitals, and daycare centers. - This close proximity facilitates the transfer of the **Sarcoptes scabiei mite** from an infected individual to others. *It spreads via airborne droplets* - Scabies mites are **not airborne** and do not spread through respiratory droplets like viruses (e.g., influenza, common cold). - Transmission requires physical contact, making airborne spread an incorrect mechanism. *The mites survive longer on surfaces* - While *Sarcoptes scabiei* mites can survive off a human host for a short period (typically 24-72 hours), their **survival on inanimate surfaces is limited** and generally not the primary mode of transmission. - Transmission mainly occurs through direct human-to-human contact. *It is transmitted through contaminated food* - Scabies is a **skin infestation** and is **not transmitted via ingestion of contaminated food**. - Foodborne illnesses are caused by pathogens in food, whereas scabies is a parasitic dermatological condition.

Practice by Chapter

Principles of Epidemiology

Practice Questions

Measures of Disease Frequency

Practice Questions

Epidemiological Study Designs

Practice Questions

Descriptive Epidemiology

Practice Questions

Analytical Epidemiology

Practice Questions

Experimental Epidemiology

Practice Questions

Screening for Disease

Practice Questions

Surveillance Systems

Practice Questions

Investigation of an Epidemic

Practice Questions

Association and Causation

Practice Questions

Modern Epidemiological Methods

Practice Questions

Critical Appraisal of Epidemiological Studies

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free