Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 681: What are case-control studies primarily used for?

A. Studying the causes of a common disease
B. Identifying multiple risk factors for a disease (Correct Answer)
C. Calculating incidence rates
D. Determining relative risk

Explanation: **Explanation** **Case-control studies** are observational analytical studies that proceed backwards from effect to cause. They compare individuals with a specific disease (cases) to those without it (controls) to determine the frequency of exposure to various risk factors. **Why Option B is Correct:** The primary strength of a case-control design is its ability to investigate **multiple potential etiologies or risk factors** for a single disease simultaneously. For example, in a study of lung cancer, researchers can investigate smoking, occupational exposure to asbestos, and air pollution all within the same study. **Why Other Options are Incorrect:** * **Option A:** Case-control studies are actually the design of choice for **rare diseases**, not common ones. Studying rare diseases via cohort studies would require an impractically large sample size. * **Option C:** **Incidence rates** cannot be calculated because the researcher determines the number of cases at the start; there is no "population at risk" followed over time. Incidence is calculated using **Cohort studies**. * **Option D:** **Relative Risk (RR)** requires incidence data. Therefore, case-control studies use the **Odds Ratio (OR)** as an estimate of the strength of association. **High-Yield Clinical Pearls for NEET-PG:** * **Direction of Study:** Retrospective (Proceeds from Effect $\rightarrow$ Cause). * **Key Metric:** **Odds Ratio (OR)** is the only measure of association derived. * **Bias:** Most prone to **Recall Bias** (cases remember exposures more vividly than controls) and **Selection Bias** (Berksonian Bias). * **Best for:** Rare diseases and diseases with long latent periods.

Question 682: Which type of study is suitable for rare diseases?

A. Cohort study
B. Case-control study (Correct Answer)
C. Both of the above
D. None of the above

Explanation: **Explanation:** The correct answer is **Case-control study**. **Why Case-control study is correct:** In epidemiology, the choice of study design depends largely on the frequency of the outcome. For **rare diseases** (e.g., specific cancers or rare genetic syndromes), a Case-control study is the most efficient and practical approach. This is because the study begins with people who already have the disease (**Cases**) and compares them to those without it (**Controls**). By starting with the outcome, researchers do not have to wait for years for the disease to develop, making it cost-effective and time-efficient for conditions with low prevalence. **Why other options are incorrect:** * **Cohort Study:** This design starts with a group of exposed and non-exposed individuals and follows them forward in time to see who develops the disease. If a disease is rare, a researcher would need to follow an enormous population for a very long time to get a statistically significant number of cases, making it expensive and impractical. (Note: Cohort studies are, however, ideal for **rare exposures**). * **Both/None:** Since the fundamental methodologies of Cohort and Case-control studies are opposites (Prospective vs. Retrospective), they are not equally suitable for rare diseases. **NEET-PG Clinical Pearls:** * **Rare Disease:** Use Case-control study. * **Rare Exposure:** Use Cohort study (e.g., exposure to a specific chemical in a factory). * **Measure of Association:** Case-control studies use **Odds Ratio (OR)**, while Cohort studies use **Relative Risk (RR)**. * **Directionality:** Case-control is "Retrospective" (Effect to Cause); Cohort is "Prospective" (Cause to Effect).

Question 683: Contraceptive efficacy is measured by?

A. Pearl Index and Life table analysis (Correct Answer)
B. Pearl Index only
C. Life table analysis and Couple protection rate
D. Pearl Index and Couple protection rate

Explanation: **Explanation:** The efficacy of a contraceptive method is determined by its ability to prevent unintended pregnancies. In epidemiology and public health, this is measured using two primary statistical tools: 1. **Pearl Index:** This is the most common method. It calculates the number of failures (pregnancies) per 100 woman-years of exposure. * *Formula:* (Total accidental pregnancies × 1200) / (Total months of exposure). 2. **Life Table Analysis:** This is considered more accurate than the Pearl Index because it calculates the "failure rate" at specific intervals (e.g., at 6 months, 12 months). It accounts for "drop-outs" or people who stop using the method mid-study, providing a cumulative failure rate over time. **Analysis of Incorrect Options:** * **Option B:** While the Pearl Index is a standard measure, it is not the *only* one. Life table analysis is often preferred in clinical trials for its precision regarding duration of use. * **Options C & D:** **Couple Protection Rate (CPR)** is a process indicator used to monitor the performance of family planning programs in a population. It measures the percentage of eligible couples effectively protected against childbirth by various methods. It measures *program coverage*, not the *biological efficacy* of the contraceptive itself. **High-Yield NEET-PG Pearls:** * **Pearl Index of Common Methods:** * No method (Chance): 80–90 * OCPs (Typical use): 9; (Perfect use): 0.3 * Copper T 380A: 0.8 * Vasectomy: 0.1 * **Lowest Failure Rate:** The Implant (Etonogestrel) currently has the lowest Pearl Index (~0.05). * **Limitation of Pearl Index:** It assumes a constant failure rate over time, whereas, in reality, failure rates usually decrease as the user becomes more experienced with the method.

Question 684: If API is greater than 2, the vector is resistant to DDT. What is the recommended frequency for malathion spraying?

A. 3 rounds of malathion every 3 months (Correct Answer)
B. 2 rounds of malathion every month
C. 1-2 rounds of malathion every 3 months
D. 1 round of malathion every month

Explanation: ### Explanation **Concept & Correct Answer:** Under the **National Vector Borne Disease Control Programme (NVBDCP)**, the strategy for Indoor Residual Spraying (IRS) is determined by the **Annual Parasite Incidence (API)** and vector resistance patterns. When the **API is >2** and the vector (Anopheles mosquito) shows resistance to DDT, the program shifts to alternative insecticides. **Malathion** is an organophosphate used in such scenarios. Because Malathion has a shorter residual effect (approximately 6–8 weeks) compared to DDT, it requires more frequent applications to maintain effective coverage throughout the transmission season. The standard protocol for Malathion IRS is **3 rounds per year**, spaced at intervals of **every 3 months** (12 weeks). **Analysis of Incorrect Options:** * **Option B & D:** Monthly spraying is logistically impractical, expensive, and unnecessary for Malathion’s degradation profile. * **Option C:** 1–2 rounds are insufficient to cover the transmission period given Malathion's shorter residual efficacy. Two rounds are typically reserved for DDT (which lasts 6 months) or Synthetic Pyrethroids. **High-Yield Clinical Pearls for NEET-PG:** * **API Threshold:** API >2 is the cut-off for "High Risk" areas requiring mandatory IRS. * **Insecticide Rotation:** * **DDT:** 2 rounds/year (Residual effect: 6 months). * **Malathion:** 3 rounds/year (Residual effect: 2–3 months). * **Synthetic Pyrethroids (e.g., Deltamethrin):** 2 rounds/year. * **Dosage:** Malathion is applied at a dosage of **2 g/m²**. * **Malathion Fogging:** Used specifically during **outbreaks** or for Aedes (Dengue) control, whereas IRS is for routine Malaria control.

Question 685: Two snake bite cases are found in Bihar. This situation is described as:

A. Epidemic
B. Pandemic
C. Sporadic (Correct Answer)
D. Endemic

Explanation: ### Explanation **Correct Answer: C. Sporadic** **Why it is correct:** The term **Sporadic** refers to the occurrence of a disease that is scattered, irregular, and infrequent. These cases occur in such a way that there is no common source of infection and no recognizable connection in time or space. In the given scenario, finding only "two cases" of snake bites in a large geographical area like Bihar indicates that these are isolated incidents without a pattern or a sudden spike in frequency. **Analysis of Incorrect Options:** * **A. Epidemic:** This refers to the occurrence of cases of an illness in a community or region clearly in excess of normal expectancy. Two cases do not constitute an "outbreak" or an excess unless the disease was previously eradicated (e.g., one case of Polio). * **B. Pandemic:** This is an epidemic that spreads across a large region, multiple continents, or worldwide (e.g., COVID-19). * **D. Endemic:** This refers to the constant presence of a disease or infectious agent within a given geographic area or population group (e.g., Goitre in sub-Himalayan regions). While snake bites occur in Bihar, the description of "two cases" specifically highlights the isolated nature of the event rather than its baseline prevalence. **High-Yield Clinical Pearls for NEET-PG:** * **Sporadic diseases** can sometimes be the starting point of an epidemic if conditions for transmission become favorable. * **Exotic diseases:** A single case of a disease not normally found in an area (e.g., Yellow Fever in India) is treated as a potential **Epidemic**. * **Epizootic:** An epidemic occurring in an animal population (e.g., Anthrax, Rabies). * **Enzootic:** An endemic disease among animals (e.g., Bovine Tuberculosis). * **Eproonitic:** An epidemic among birds (e.g., Bird Flu).

Question 686: Which of the following study designs does NOT allow for the determination of cause to progression?

A. Case-control study (Correct Answer)
B. Cohort study
C. Randomized controlled trial
D. Ecological study

Explanation: ### Explanation The core of this question lies in the **directionality** of the study design. To determine the progression from a cause (exposure) to an effect (outcome), a study must be **prospective** or longitudinal in nature. **1. Why Case-Control Study is the Correct Answer:** A case-control study is inherently **retrospective**. It starts with the "effect" (cases who already have the disease) and looks backward in time to identify "causes" (past exposures). Because it begins after the disease has already developed, it cannot observe the actual transition or **progression** from a healthy state to a diseased state. It can only determine an association (Odds Ratio), not the sequence of progression. **2. Why the Other Options are Incorrect:** * **Cohort Study:** This is the gold standard for determining progression. It starts with exposed and non-exposed individuals and follows them forward in time to see who develops the disease, allowing for the calculation of **Incidence** and **Relative Risk**. * **Randomized Controlled Trial (RCT):** Like a cohort study, an RCT is prospective. It follows participants from the point of intervention (cause) to the clinical outcome (progression), providing the strongest evidence for causality. * **Ecological Study:** While it deals with populations rather than individuals, it can observe changes in exposure and outcome over time (Time Series Analysis), allowing for some observation of progression at a macro level, unlike the backward-looking case-control design. **Clinical Pearls for NEET-PG:** * **Directionality:** Case-control is "Effect to Cause"; Cohort is "Cause to Effect." * **Incidence:** Can only be calculated in Cohort studies/RCTs, not Case-control. * **Rare Diseases:** Case-control is the best design for rare diseases. * **Rare Exposures:** Cohort study is the best design for rare exposures. * **Nesting:** A "Nested Case-Control" study is actually conducted within a Cohort study to combine the benefits of both.

Question 687: A 9-month-old, unimmunized child can be given which of the following vaccinations in a single visit?

A. BCG
B. BCG, DPT - 1, OPV - 1
C. DPT - 1, OPV - 1, Measles
D. BCG, DPT-1, OPV - 1, Measles (Correct Answer)

Explanation: **Explanation:** The core concept tested here is the **National Immunization Schedule (NIS)** guidelines regarding "catch-up" vaccination for a late-starter child. According to the Universal Immunization Programme (UIP), if a child presents late for immunization, all due vaccines for which the child is eligible should be administered simultaneously at different injection sites. **Why Option D is Correct:** * **BCG:** Can be given anytime from birth up to **1 year** of age. Since the child is 9 months old, BCG is still indicated. * **DPT-1 & OPV-1:** These are part of the primary series. The first dose can be initiated as late as 1 year (for DPT) or 5 years (for OPV). * **Measles (MR-1):** The scheduled age for the first dose of Measles/MR vaccine is **9 completed months**. Since the child is 9 months old and unimmunized, they are eligible for all four vaccines. Administering them in a single visit ensures early protection and reduces "missed opportunities." **Analysis of Incorrect Options:** * **Option A & B:** These are incomplete. While BCG, DPT, and OPV can be given, they ignore the fact that at 9 months, the child is now also eligible for the Measles vaccine. * **Option C:** This ignores BCG. A common misconception is that BCG cannot be given after the neonatal period; however, it remains valid until the first birthday. **High-Yield Pearls for NEET-PG:** 1. **BCG Limit:** Up to 1 year. If given after 1 month, the dose is **0.1 ml** (instead of 0.05 ml). 2. **DPT Limit:** The primary series can be started up to **1 year** of age. If the child is >1 year but <7 years, DPT is replaced by DT (Pentavalent is also not given after 1 year). 3. **OPV Limit:** Can be given up to **5 years** of age. 4. **Measles Limit:** Can be given up to **5 years** of age. 5. **Site Rule:** Multiple injections should be given at different sites (e.g., BCG on left upper arm, DPT on anterolateral thigh, Measles on right upper arm).

Question 688: Which age group is included when calculating the child mortality rate?

A. Children less than 5 years
B. Children less than 10 years
C. Children aged 1-4 years (Correct Answer)
D. Children aged 10-15 years

Explanation: **Explanation:** The **Child Mortality Rate (CMR)**, also known as the Under-5 Mortality Rate in some contexts but specifically defined in epidemiology as the **1–4 year mortality rate**, refers to the number of deaths of children aged 12–59 months per 1,000 children in the same age group per year. It is a sensitive indicator of the socio-economic development, environmental sanitation, and nutritional status of a community. **Why Option C is Correct:** The standard epidemiological definition for "Child Mortality Rate" specifically targets the **1–4 year age group**. This period is critical as it reflects deaths due to preventable causes like malnutrition, diarrheal diseases, and acute respiratory infections, which are often distinct from the neonatal causes that dominate infant mortality. **Analysis of Incorrect Options:** * **Option A (Less than 5 years):** This refers to the **Under-5 Mortality Rate (U5MR)**. While often confused with CMR, U5MR includes everyone from birth up to the 5th birthday (0–5 years). * **Option B & D:** These age groups (less than 10 or 10–15 years) are not standard indicators for mortality rates in public health surveillance; the latter falls under adolescent health. **High-Yield Clinical Pearls for NEET-PG:** * **Infant Mortality Rate (IMR):** Deaths from 0–1 year per 1,000 live births. * **Neonatal Mortality Rate:** Deaths within the first 28 days of life. * **Child Mortality Rate Formula:** (Number of deaths at age 1–4 years in a year / Total number of children aged 1–4 years at mid-year) × 1,000. * **Key Indicator:** CMR is considered a better indicator of **social development** than IMR, as it is less influenced by biological/obstetric factors and more by the environment and nutrition.

Question 689: What is a characteristic of a diagnostic test when compared to a screening test?

A. Test results are arbitrary and final
B. Based on one criterion or cut-off point
C. Less accurate
D. Done on those with indications or who are sick (Correct Answer)

Explanation: ### Explanation The fundamental difference between screening and diagnostic tests lies in their **purpose and target population**. **Why the correct answer is right:** A **diagnostic test** is performed on individuals who have symptoms or signs of a disease (symptomatic) or those who have tested positive during a screening process. Its primary goal is to establish or confirm a diagnosis to initiate treatment. In contrast, a screening test is applied to apparently healthy or asymptomatic individuals to detect those who are likely to have the disease. **Analysis of Incorrect Options:** * **A. Test results are arbitrary and final:** While diagnostic tests are considered "final" for clinical decision-making, the results are **not arbitrary**. They are based on definitive evidence (like a biopsy or culture) and are used as the "Gold Standard." * **B. Based on one criterion or cut-off point:** This is a characteristic of **screening tests**, which often use a single cut-off (e.g., blood sugar levels) to maximize sensitivity. Diagnostic tests are often more complex, involving a combination of clinical signs, symptoms, and multiple laboratory findings. * **C. Less accurate:** Diagnostic tests are **more accurate** (higher specificity) than screening tests. Screening tests prioritize sensitivity (to not miss cases), whereas diagnostic tests prioritize specificity and positive predictive value to ensure the diagnosis is correct before starting potentially invasive treatments. --- ### NEET-PG High-Yield Pearls: Screening vs. Diagnosis | Feature | Screening Test | Diagnostic Test | | :--- | :--- | :--- | | **Target Population** | Apparently healthy/Asymptomatic | Symptomatic/Indications | | **Goal** | Early detection (Case finding) | Confirmation of disease | | **Test Quality** | High Sensitivity (to minimize False Negatives) | High Specificity (to minimize False Positives) | | **Cost** | Low (applied to masses) | High (applied to individuals) | | **Basis for Treatment** | Not a basis for treatment | Basis for treatment | **Key Concept:** A screening test is a preliminary step; a diagnostic test is the definitive step. In epidemiology, the "Gold Standard" is always a diagnostic test.

Question 690: Who is considered the 'Father of Public Health'?

A. Tuberculosis
B. Cholera (Correct Answer)
C. Malaria
D. Plague

Explanation: **Explanation:** In the history of medicine, **Cholera** is famously referred to as the **"Father of Public Health."** This title is attributed to the disease because the massive cholera pandemics of the 19th century acted as the primary catalyst for the birth of modern public health infrastructure. The 1854 Broad Street pump outbreak in London led **John Snow** (the Father of Modern Epidemiology) to prove that cholera was waterborne, debunking the "Miasma theory." These outbreaks forced governments to enact the first major Public Health Acts, leading to organized sanitary reforms, protected water supplies, and sewage disposal systems. Thus, the disease itself "fathered" the discipline of public health by necessitating its creation. **Analysis of Incorrect Options:** * **Tuberculosis:** Often called the "Captain of All These Men of Death" or the "White Plague," it is a major social disease but did not initiate the formal public health movement in the same way cholera did. * **Malaria:** Known as the "King of Diseases," it is a significant global health burden but is not associated with the origin of the public health discipline. * **Plague:** Known as the "Black Death," it led to the concept of **Quarantine** (first practiced in Venice), but the title "Father of Public Health" remains specific to Cholera. **NEET-PG High-Yield Pearls:** * **John Snow:** Father of Modern Epidemiology (linked to Cholera). * **Louis Pasteur:** Father of Public Health (when referring to a *person* rather than a disease). * **Cholera:** Also known as the "Father of Public Health" because it led to the **1848 Public Health Act** in the UK. * **First International Sanitary Conference (1851):** Was held specifically to discuss the international control of Cholera.

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