Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1171: During an epidemic of hepatitis E, in which demographic group is fatality maximum?

A. Infants
B. Adolescents
C. Pregnant women (Correct Answer)
D. Malnourished males

Explanation: **Explanation:** Hepatitis E Virus (HEV) is a water-borne RNA virus (Hepeviridae family) that typically causes a self-limiting acute viral hepatitis. However, it is notorious for its high Case Fatality Rate (CFR) among **pregnant women**, particularly during the **third trimester**. **1. Why Pregnant Women?** While the overall CFR for Hepatitis E in the general population is low (0.5–4%), it escalates dramatically to **15–25%** in pregnant women. The underlying pathophysiology involves a combination of altered immune responses (shift in Th1/Th2 balance), high viral loads, and a high risk of developing **Fulminant Hepatic Failure (FHF)**. Complications like Disseminated Intravascular Coagulation (DIC) and encephalopathy are common causes of death in this group. **2. Analysis of Incorrect Options:** * **Infants:** While infants are vulnerable to many infections, HEV is generally mild or asymptomatic in children. * **Adolescents:** This group typically experiences a self-limiting course of the disease with very low mortality. * **Malnourished males:** While malnutrition can worsen the prognosis of any infection, it does not specifically predispose males to the extreme fatality rates seen in pregnancy for HEV. **3. High-Yield Clinical Pearls for NEET-PG:** * **Route of Transmission:** Fecal-oral (most common). * **Incubation Period:** 2–8 weeks (Average: 40 days). * **Genotypes:** Genotypes 1 and 2 are associated with human epidemics; Genotypes 3 and 4 are zoonotic (pork consumption). * **Chronic Infection:** HEV can cause chronic hepatitis in **immunocompromised** individuals (e.g., organ transplant recipients). * **Prevention:** HEV 239 (Hecolin) is a vaccine available in some countries, though not yet part of the routine schedule in India.

Question 1172: What is an example of primary prevention?

A. Marriage counseling (Correct Answer)
B. Early diagnosis and treatment
C. Pap smear
D. Self breast examination

Explanation: **Explanation:** **Primary prevention** aims to prevent the onset of a disease or disorder by reducing exposure to risk factors or increasing resistance. It is applied during the **pre-pathogenesis phase** of a disease. * **Why Marriage Counseling is Correct:** Marriage counseling is a form of **Health Promotion**, which is a key mode of intervention in primary prevention. It aims to improve mental health, social well-being, and prevent future psychosocial disorders or domestic disharmony before they occur. Other examples include nutritional interventions, environmental sanitation, and health education. **Analysis of Incorrect Options:** * **B. Early diagnosis and treatment:** This is the hallmark of **Secondary Prevention**. It aims to arrest the disease process and prevent complications after the disease has already started but is in its early stages. * **C. Pap smear:** This is a screening tool for cervical cancer. All screening tests (except for neonatal screening in some contexts) are classified as **Secondary Prevention** because they detect the disease in the asymptomatic period. * **D. Self-breast examination:** This is a method for early detection of breast lumps. Like other screening activities, it falls under **Secondary Prevention**. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Prevention** includes two modes: **Health Promotion** (e.g., counseling, exercise) and **Specific Protection** (e.g., Immunization, Vitamin A prophylaxis, use of helmets). * **Primordial Prevention:** Prevention of the *emergence* of risk factors (e.g., discouraging children from starting smoking). * **Tertiary Prevention:** Focuses on **Disability Limitation** and **Rehabilitation** (e.g., physiotherapy after a stroke).

Question 1173: A woman is a carrier for an X-linked disease. The disease frequency in the population is 1 in 2,000. What fraction of women in this population are carriers for this particular disease?

A. 1 in 500
B. 1 in 1,000 (Correct Answer)
C. 1 in 1,500
D. 1 in 2,000

Explanation: ### Explanation This question tests the application of the **Hardy-Weinberg Principle** in the context of X-linked recessive disorders. **1. Why the Correct Answer is Right:** In X-linked recessive diseases, the frequency of the disease in the population is equal to the frequency of the disease-causing allele (**q**) because males have only one X chromosome. * Given: Disease frequency ($q$) = $1/2,000$. * The frequency of female carriers (heterozygotes) is represented by **$2pq$**. * Since $q$ is very small ($1/2,000$), $p$ (the normal allele frequency) is approximately **1**. * Calculation: Carrier frequency = $2 \times 1 \times (1/2,000) = 2/2,000 = \mathbf{1/1,000}$. **2. Why the Incorrect Options are Wrong:** * **Option A (1 in 500):** This would be the carrier frequency if the disease frequency ($q$) were $1/1,000$. * **Option C (1 in 1,500):** This value does not align with the $2pq$ calculation based on the provided $q$. * **Option D (1 in 2,000):** This is the frequency of the disease in males ($q$). It fails to account for the fact that carriers are $2pq$. **3. Clinical Pearls & High-Yield Facts:** * **Rule of Thumb:** For rare X-linked recessive traits, the carrier frequency in females is approximately **twice** the disease frequency in males ($2q$). * **Hardy-Weinberg Equation:** $p^2 + 2pq + q^2 = 1$. * **Male vs. Female Frequency:** In X-linked conditions, males are either $p$ (normal) or $q$ (affected). Females can be $p^2$ (normal), $2pq$ (carrier), or $q^2$ (affected). * **Common Examples:** Hemophilia A/B, Duchenne Muscular Dystrophy, and Color Blindness follow this inheritance pattern.

Question 1174: Which sampling method is best for an inhomogeneous population?

A. Cluster Sampling
B. Stratified random sampling (Correct Answer)
C. Systematic random sampling
D. Simple random sampling

Explanation: **Explanation:** **1. Why Stratified Random Sampling is Correct:** In an **inhomogeneous (heterogeneous) population**, individuals possess diverse characteristics (e.g., different age groups, socio-economic statuses, or disease severities) that may influence the study outcome. Stratified random sampling is the gold standard here because it involves dividing the population into homogenous subgroups called **"strata"** based on these characteristics. A random sample is then drawn from each stratum. This ensures that even small subgroups are represented proportionately, reducing sampling error and increasing the precision of the results compared to simple random sampling. **2. Why Other Options are Incorrect:** * **Simple Random Sampling:** Best suited for small, **homogeneous** populations where every individual has an equal chance of being selected. In an inhomogeneous population, it risks omitting smaller but important subgroups. * **Systematic Random Sampling:** Involves picking every $n^{th}$ individual from a list. While easy to implement, it assumes the sampling frame is randomly ordered. If there is a hidden periodicity in the population, it introduces bias. * **Cluster Sampling:** Used when the population is large and widely scattered (e.g., a whole city). It involves sampling intact groups (clusters) rather than individuals. While administratively convenient, it is actually **less precise** for inhomogeneous populations because individuals within a cluster tend to be similar to each other. **3. High-Yield Pearls for NEET-PG:** * **Stratified Sampling:** Think "Inhomogeneous population" or "Subgroup representation." * **Cluster Sampling:** Think "Large geographical area" or "WHO EPI coverage surveys" (30 x 7 cluster technique). * **Systematic Sampling:** Think "Linear pattern" or "Sampling interval ($K = N/n$)." * **Snowball Sampling:** Best for "Hidden populations" (e.g., IV drug users, commercial sex workers).

Question 1175: Which of the following is NOT included in the Revised National Tuberculosis Control Programme (RNTCP)?

A. X-ray is diagnostic
B. Directly observed treatment
C. Active case finding (Correct Answer)
D. Drugs given daily

Explanation: The RNTCP (now renamed the **National TB Elimination Programme - NTEP**) is primarily based on the **DOTS strategy**, which emphasizes **Passive Case Finding**. This means the program relies on symptomatic patients voluntarily reporting to health facilities rather than health workers searching for cases in the community. ### Why "Active Case Finding" is the Correct Answer: Under standard RNTCP/NTEP guidelines, the core strategy is passive case finding to ensure that those with symptoms (cough >2 weeks) are diagnosed. While active case finding (ACF) is conducted in specific high-risk vulnerable populations (e.g., slums, prisons), it is **not** the primary diagnostic strategy of the program. ### Explanation of Other Options: * **X-ray is diagnostic:** Under the updated NTEP algorithms, Chest X-ray is used as a primary screening tool. If the X-ray is suggestive of TB, the patient is then subjected to molecular testing (CBNAAT/Truenat) for confirmation. * **Directly observed treatment:** This remains a pillar of the program. A treatment supporter ensures the patient swallows the medication to prevent default and drug resistance. * **Drugs given daily:** Since 2017, the RNTCP shifted from intermittent (thrice weekly) regimens to **Daily Regimens** using Fixed-Dose Combinations (FDCs) to maintain higher peak plasma concentrations. ### High-Yield Pearls for NEET-PG: * **Diagnosis:** The "Gold Standard" for diagnosis in NTEP is now **Molecular Tests (CBNAAT/Truenat)**, not sputum microscopy. * **Goal:** India aims to **Eliminate TB by 2025**, five years ahead of the global SDG target of 2030. * **Nikshay Poshan Yojana:** Provides ₹500/month nutritional support to all TB patients. * **Definition of Elimination:** < 1 case per 1,000,000 (1 million) population.

Question 1176: To which vaccine does the Open Vial Policy apply?

A. Measles
B. BCG
C. Japanese encephalitis vaccine
D. Hepatitis B (Correct Answer)

Explanation: ### Explanation The **Open Vial Policy (OVP)**, introduced by the WHO and adopted by India’s Universal Immunization Programme (UIP), allows certain multi-dose vaccine vials to be used for up to **28 days** after opening, provided specific storage conditions and potency criteria (VVM) are met. **1. Why Hepatitis B is Correct:** The Open Vial Policy applies to vaccines that are **liquid formulations** and contain **preservatives** (like Thiomersal) to prevent bacterial contamination. **Hepatitis B**, along with DPT, Pentavalent, Oral Polio Vaccine (OPV), Tetanus-Diphtheria (Td), and Injectable Polio Vaccine (IPV), falls under this category. These vaccines do not lose potency rapidly after opening and are not prone to serious contamination if handled correctly. **2. Why the Other Options are Incorrect:** * **Measles, BCG, and Japanese Encephalitis (JE):** These are **lyophilized (freeze-dried) vaccines**. Once reconstituted with a diluent, they do not contain preservatives and are highly unstable. They carry a high risk of bacterial contamination (e.g., *Staphylococcal* Toxic Shock Syndrome). Therefore, they must be discarded within **6 hours** of opening or at the end of the session, whichever is earlier. The Open Vial Policy **does not** apply to reconstituted vaccines. **3. High-Yield Clinical Pearls for NEET-PG:** * **Criteria for OVP:** 1) The vaccine is not expired; 2) Stored at 2°C to 8°C; 3) VVM is intact (inner square lighter than outer circle); 4) Aseptic technique was used. * **Exceptions to OVP:** It applies only to fixed session sites (PHCs/Hospitals), not to outreach sessions (where vials must be discarded at the end of the day). * **Memory Aid:** "Liquid = 28 days (OVP applies); Reconstituted = 6 hours (OVP does not apply)."

Question 1177: Herd immunity is not important in which of the following conditions?

A. Tetanus (Correct Answer)
B. Pertussis
C. Diphtheria
D. All

Explanation: ### Explanation **1. Why Tetanus is the Correct Answer:** Herd immunity (community immunity) refers to the indirect protection from an infectious disease that happens when a large percentage of a population becomes immune, thereby stopping the **person-to-person chain of transmission**. Tetanus is unique because it is **not a communicable disease**. It is caused by the spores of *Clostridium tetani* found in soil and animal manure. Infection occurs through environmental exposure (wounds or umbilical stumps), not through contact with an infected individual. Since there is no human-to-human transmission to interrupt, immunizing 99% of the population provides zero protection to the remaining 1% unvaccinated individuals. Therefore, herd immunity does not apply to Tetanus. **2. Why the Other Options are Incorrect:** * **Pertussis (Whooping Cough):** This is a highly contagious respiratory infection spread via droplets. High vaccination coverage reduces the reservoir of *Bordetella pertussis* in the community, protecting unvaccinated infants. * **Diphtheria:** Caused by *Corynebacterium diphtheriae*, it spreads through respiratory droplets or direct contact. Mass immunization (DPT/Pentavalent) creates herd immunity by reducing the carrier state and limiting outbreaks. **3. NEET-PG High-Yield Pearls:** * **Definition:** Herd immunity is the "threshold of immunity" required to stop the spread of a disease in a community. * **Prerequisites for Herd Immunity:** 1. The disease agent must be restricted to a single host species (Humans). 2. Transmission must be direct (person-to-person). 3. Infection must induce solid immunity. * **Key Examples:** Herd immunity is effective in **Polio, Measles, Mumps, and Rubella**. * **The Tetanus Exception:** Tetanus is the classic example used in exams for a vaccine-preventable disease where herd immunity is **absent**. Protection is purely individual.

Question 1178: Which of the following screening methods is used under the Revised National Tuberculosis Control Program (RNTCP)?

A. Active screening
B. Passive screening (Correct Answer)
C. Mass screening
D. All of the above

Explanation: **Explanation:** The **Revised National Tuberculosis Control Program (RNTCP)**, now renamed the **National TB Elimination Program (NTEP)**, primarily relies on **Passive Case Finding (Passive Screening)**. 1. **Why Passive Screening is Correct:** Passive screening involves identifying cases among individuals who voluntarily seek medical care because they are experiencing symptoms (e.g., chronic cough, fever). In the context of TB control in India, the strategy focuses on testing "chest symptomatics" who report to health facilities. This is the most cost-effective and sustainable method for a high-burden country, ensuring that those with the highest bacterial load (and thus the highest transmission risk) are diagnosed and treated. 2. **Why Other Options are Incorrect:** * **Active Screening:** This involves health workers proactively searching for cases in the community (e.g., door-to-door surveys). While NTEP has introduced "Active Case Finding" (ACF) for high-risk vulnerable populations (like slum dwellers or miners), it is not the primary screening method for the general program. * **Mass Screening:** This refers to screening the entire population regardless of symptoms (e.g., mass miniature radiography). This is not recommended due to low yield, high cost, and poor cost-benefit ratio. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Tool:** The mainstay of diagnosis under NTEP is **Sputum Smear Microscopy** (traditionally) and increasingly **Molecular Tests (CBNAAT/Truenat)** as the first-line diagnostic. * **Target Group:** Passive screening targets "Presumptive TB cases" (any person with a cough of 2 weeks or more). * **Active Case Finding (ACF):** Remember that ACF is a *supplementary* strategy implemented periodically for "vulnerable groups" only, not the standard operational procedure for the general public. * **Goal:** The NTEP aims for "Universal Access" to quality TB diagnosis and treatment.

Question 1179: A country has a population of 1000 million, a birth rate of 23, and a death rate of 6. In which phase of the demographic cycle does this country lie?

A. Early expanding
B. Late expanding (Correct Answer)
C. Plateau
D. Declining

Explanation: ### Explanation The demographic cycle describes the transition of a population over time based on changes in birth and death rates. To identify the correct phase, we must calculate the **Natural Growth Rate (NGR)**: * **Birth Rate (BR):** 23 per 1000 * **Death Rate (DR):** 6 per 1000 * **NGR:** BR - DR = 17 per 1000 (or 1.7%) **Why "Late Expanding" is correct:** In the **Late Expanding phase**, the death rate has already declined significantly and reached a low level, while the birth rate begins to fall but still remains higher than the death rate. This leads to continued population growth, but at a slowing pace. A birth rate in the low 20s and a death rate in single digits (as seen in India currently) are classic indicators of this stage. **Analysis of Incorrect Options:** * **Early Expanding:** Characterized by a high birth rate and a *falling* death rate. The birth rate is typically >30-35, and the death rate is still relatively high compared to the late stage. * **Plateau (Low Stationary):** Both birth and death rates are very low and roughly equal, leading to zero population growth. * **Declining:** The birth rate falls below the death rate, leading to a negative growth rate (e.g., Germany, Japan). **High-Yield NEET-PG Pearls:** * **India's Status:** India is currently in the **Late Expanding phase**. * **First Stage (High Stationary):** High BR and high DR (e.g., pre-industrial societies). * **Demographic Gap:** The difference between BR and DR; it is widest at the end of the Early Expanding/beginning of the Late Expanding phase. * **Key Indicator:** The transition from Stage 2 to Stage 3 is primarily driven by a decline in fertility (Birth Rate).

Question 1180: Active search for disease in an apparently healthy individual is known as:

A. Monitoring
B. Case finding
C. Screening (Correct Answer)
D. Sentinel surveillance

Explanation: **Explanation:** **1. Why Screening is Correct:** Screening is defined as the presumptive identification of unrecognized disease in an **apparently healthy (asymptomatic)** individual by means of rapidly applied tests, examinations, or other procedures. The primary objective is to detect the disease at an early stage (pre-symptomatic phase) to initiate treatment and improve prognosis. It is a proactive, "active search" initiated by the healthcare provider rather than the patient. **2. Why Other Options are Incorrect:** * **Monitoring:** This refers to the routine measurement and analysis of signals to detect changes in environment or health status. It is a continuous process (e.g., monitoring growth in children or water quality), not a one-time search for disease. * **Case Finding:** This is often confused with screening. Case finding (or opportunistic screening) occurs when a patient visits a doctor for a specific complaint, and the doctor tests them for an **unrelated** condition (e.g., checking BP in a patient presenting with a fracture). It is restricted to patients already seeking medical care. * **Sentinel Surveillance:** This is a method for identifying "missing cases" and estimating the total disease burden in a community by monitoring a specific sub-population or "sentinel sites" (e.g., monitoring HIV in STD clinics). It is used for trend analysis, not individual diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Screening vs. Diagnosis:** Screening is done on apparently healthy people (high sensitivity), while Diagnostic tests are done on those with symptoms (high specificity). * **Iceberg Phenomenon:** Screening is used to detect the "submerged portion" of the iceberg (unmet need/asymptomatic cases). * **Wilson and Jungner Criteria:** These are the gold standard criteria used to decide if a disease should be screened (e.g., the condition should be an important health problem with a recognizable latent stage).

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Principles of Epidemiology

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Measures of Disease Frequency

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Epidemiological Study Designs

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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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