Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 391: Smoking is the cause of 85% of lung cancers that occurred within a group of smokers. This is an example of which of the following statistics?

A. Population attributable risk
B. Odds ratio
C. Attributable risk (Correct Answer)
D. Relative risk

Explanation: ### Explanation The correct answer is **Attributable Risk (AR)**. **1. Why Attributable Risk is correct:** Attributable Risk (also known as Risk Difference) represents the amount of disease incidence that can be directly attributed to a specific exposure. When expressed as a percentage (**Attributable Risk Proportion**), it indicates the proportion of the disease in the **exposed group** that could be eliminated if the exposure were removed. * **Formula:** $\frac{I_e - I_u}{I_e} \times 100$ (where $I_e$ is incidence in exposed and $I_u$ is incidence in unexposed). * In this question, stating that 85% of lung cancers *within the group of smokers* are due to smoking directly matches this definition. **2. Why other options are incorrect:** * **Population Attributable Risk (PAR):** This measures how much of the disease in the **entire population** (both smokers and non-smokers) is due to the exposure. It depends on the prevalence of the exposure in the community. * **Relative Risk (RR):** This is a ratio ($I_e / I_u$) that measures the **strength of association** between exposure and disease. It tells us how many times more likely an exposed person is to develop the disease compared to an unexposed person, but not the actual proportion of cases caused by it. * **Odds Ratio (OR):** This is the measure of association used in **Case-Control studies**. It estimates the odds of exposure among cases versus controls. **3. NEET-PG High-Yield Pearls:** * **Relative Risk (RR)** is the best indicator of the **etiological role** of a factor. * **Attributable Risk (AR)** is the best indicator of the **public health impact** of an exposure on the exposed group. * **Population Attributable Risk (PAR)** is most useful for **prioritizing public health programs** and resource allocation. * If a question mentions "within the exposed group," think **AR**. If it mentions "in the community/total population," think **PAR**.

Question 392: What is the best indicator of the trend of Tuberculosis, unaffected by current control measures?

A. Annual risk of infection (Correct Answer)
B. Prevalence of TB infection
C. Percentage of primary drug resistance
D. Percentage of multidrug resistance

Explanation: ### Explanation **1. Why "Annual Risk of Infection" (ARI) is correct:** The Annual Risk of Infection (also known as the **Tuberculin Conversion Index**) represents the proportion of the population that will be newly infected with *Mycobacterium tuberculosis* over the course of one year. It is considered the **best indicator of the trend of TB** in a community because it reflects the overall "force of infection." Crucially, ARI is relatively **unaffected by current control measures** (like DOTS or chemotherapy) because it measures the risk of *infection* (transmission) rather than the prevalence of *disease*. While treatment reduces the duration of infectiousness, the ARI provides a stable, long-term longitudinal view of the transmission dynamics within a community, making it the "gold standard" for monitoring the impact of TB programs over decades. **2. Why the other options are incorrect:** * **Prevalence of TB infection:** This represents the total pool of infected individuals (old and new). It is influenced by past transmission rates and population aging, making it a less sensitive indicator of *current* trends compared to ARI. * **Percentage of Primary/Multidrug Resistance:** These indicators measure the **quality of the TB control program** and the efficacy of drug regimens. While vital for clinical management, they reflect the biological evolution of the bacteria and treatment compliance rather than the fundamental epidemiological trend of the disease in the general population. **3. NEET-PG High-Yield Pearls:** * **ARI Calculation:** In India, an ARI of 1% roughly corresponds to an incidence of 75–100 new smear-positive cases per 100,000 population per year. * **Prevalence vs. Incidence:** Prevalence is the best indicator for estimating the **burden of disease**, while ARI is the best for **transmission trends**. * **Sputum Positivity:** The most important factor in determining the ARI is the density of smear-positive cases in the community.

Question 393: All of the following represent specific protection modes of disease prevention except?

A. Chemoprophylaxis for meningococcal meningitis
B. Personal hygiene and environmental sanitation (Correct Answer)
C. Usage of condoms
D. Iodization of salt

Explanation: **Explanation:** The concept of **Levels of Prevention** is a high-yield topic in Epidemiology. Prevention is divided into Primordial, Primary, Secondary, and Tertiary levels. **Primary Prevention** specifically consists of two modes of intervention: **Health Promotion** and **Specific Protection**. **Why Option B is the correct answer:** Personal hygiene and environmental sanitation are classified under **Health Promotion**. Health Promotion involves non-specific measures aimed at strengthening the host and improving the general environment (e.g., health education, nutrition, and lifestyle changes). Since the question asks for the "except" option, B is correct because it is not a "specific" measure targeted at a single disease. **Analysis of Incorrect Options (Specific Protection):** Specific Protection involves activities directed against a particular disease or group of diseases. * **A. Chemoprophylaxis:** Administering Rifampicin or Ciprofloxacin for Meningococcal meningitis is a specific pharmacological intervention to prevent a single pathogen. * **C. Usage of Condoms:** This is a specific mechanical barrier method used to prevent STIs (like HIV/Syphilis) and unwanted pregnancy. * **D. Iodization of Salt:** This is a specific nutritional intervention aimed at preventing Iodine Deficiency Disorders (IDD). **High-Yield NEET-PG Pearls:** * **Primary Prevention:** Occurs in the *Pre-pathogenesis* phase. * **Specific Protection Examples:** Immunization, Vitamin A prophylaxis, use of helmets/seatbelts, and protection against occupational hazards. * **Secondary Prevention:** Focuses on "Early Diagnosis and Treatment" (e.g., Pap smears, Sputum for AFB). * **Tertiary Prevention:** Focuses on "Disability Limitation and Rehabilitation."

Question 394: Which of the following is a component of PQLI?

A. Neonatal mortality rate
B. Infant mortality rate (Correct Answer)
C. Perinatal mortality rate
D. None of the above

Explanation: The **Physical Quality of Life Index (PQLI)** is a composite index used to measure the quality of life or well-being of a country. It was developed by Morris David Morris in the mid-1970s as a non-economic alternative to Gross National Product (GNP). ### Why Option B is Correct The PQLI is calculated based on three specific indicators, each weighted equally on a scale of 0 to 100: 1. **Infant Mortality Rate (IMR):** Reflects the quality of the healthcare system and environmental conditions. 2. **Life Expectancy at Age 1:** Note that it is specifically at age 1, not at birth (to avoid double-counting IMR). 3. **Basic Literacy Rate:** Reflects the educational status of the population. ### Why Other Options are Incorrect * **Option A (Neonatal Mortality Rate):** While NMR is a sensitive indicator of newborn care and maternal health, it is not a component of the PQLI. * **Option C (Perinatal Mortality Rate):** This measures late fetal deaths and early neonatal deaths. It is an indicator of obstetric and pediatric care but is not used in the PQLI calculation. ### High-Yield Clinical Pearls for NEET-PG * **Range:** PQLI scores range from **0 (worst) to 100 (best)**. * **PQLI vs. HDI:** Unlike the Human Development Index (HDI), PQLI **does not include per capita income** (economic growth). * **HDI Components:** For comparison, the HDI includes Life expectancy at birth, Mean/Expected years of schooling, and Gross National Income (GNI) per capita. * **The "Age 1" Rule:** A common trap in exams is "Life expectancy at birth." Remember, PQLI uses **Life expectancy at Age 1**.

Question 395: Which of the following is NOT a condition in which healthy carriers are commonly found?

A. Typhoid (Correct Answer)
B. Cholera
C. Diphtheria
D. Pertussis

Explanation: **Explanation** The core concept tested here is the classification of carriers based on their clinical state. A **Healthy Carrier** is an individual who harbors the pathogen but has never suffered from the clinical disease (subclinical infection). In contrast, a **Chronic Carrier** is someone who continues to harbor the pathogen for months or years *following* an attack of the disease. **1. Why Typhoid is the correct answer:** In **Typhoid (Enteric fever)**, carriers are almost exclusively **convalescent** or **chronic carriers**. They harbor *Salmonella typhi* in the gallbladder or biliary tract (or urinary tract) following a clinical bout of the disease. While subclinical infections occur, the classic "carrier state" associated with Typhoid (like the famous Mary Mallon) follows a clinical infection, making "Healthy Carrier" an inappropriate classification for the primary epidemiological reservoir of Typhoid. **2. Analysis of Incorrect Options:** * **Cholera:** Healthy carriers (subclinical cases) are very common. In *Vibrio cholerae* (especially El Tor), the ratio of healthy carriers to clinical cases can be as high as 50:1 to 100:1. * **Diphtheria:** Healthy carriers are the primary reservoir for *Corynebacterium diphtheriae*. They outnumber clinical cases and are crucial for the continued transmission of the bacteria in the community. * **Pertussis:** While less common than in Diphtheria, healthy (asymptomatic) carriers do exist and contribute to the transmission of *Bordetella pertussis*, especially in immunized populations where the infection may not manifest clinically. **High-Yield Clinical Pearls for NEET-PG:** * **Typhoid:** The chronic carrier state is more common in **females** and those with **gallstones**. * **Measles:** Does **NOT** have a carrier state (only clinical cases). * **Incubatory Carriers:** Seen in Measles, Mumps, Polio, and Hepatitis B. * **Convalescent Carriers:** Seen in Typhoid, Dysentery, and Pertussis.

Question 396: What was the gas responsible for the Bhopal gas tragedy?

A. Methyl isocyanate (Correct Answer)
B. Potassium iso thiocyanate
C. Sodium isothiocyanate
D. Ethyl isothiocyanate

Explanation: The Bhopal Gas Tragedy, which occurred on the night of December 2–3, 1984, is considered the world's worst industrial disaster. It was caused by the accidental release of over 40 tons of **Methyl Isocyanate (MIC)** gas from the Union Carbide India Limited (UCIL) pesticide plant. **Explanation of the Correct Option:** * **Methyl Isocyanate (MIC):** MIC is an extremely toxic, volatile, and colorless liquid used in the production of carbamate pesticides (like Sevin/Carbaryl). When it leaked, it reacted with water in the atmosphere to form a dense cloud that settled over the city. Pathologically, it causes severe mucosal irritation, pulmonary edema, and secondary complications due to its high reactivity with proteins and DNA. **Explanation of Incorrect Options:** * **Potassium/Sodium Isothiocyanate:** These are inorganic salts often used in chemical synthesis or as analytical reagents. They do not exist as volatile gases and were not involved in the pesticide manufacturing process at the Bhopal plant. * **Ethyl Isothiocyanate:** While chemically related, this compound is primarily used in organic synthesis and as a flavoring agent (mustard oil derivative). It lacks the extreme industrial toxicity and historical association linked to the Bhopal disaster. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote Controversy:** Sodium Thiosulfate was initially suggested as an antidote based on the theory of cyanide poisoning, though its efficacy remains debated. * **Health Impacts:** The immediate cause of death for most victims was **asphyxiation due to acute pulmonary edema**. Long-term survivors suffer from chronic obstructive lung disease, restrictive lung disease, and ophthalmic issues (corneal opacities). * **Environmental Health:** This event led to the enactment of the **Environment Protection Act (1986)** in India.

Question 397: What are the true targets for DOTS in terms of case finding and cure rate?

A. Case finding 80%, cure rate 85%
B. Case finding 80%, cure rate 80%
C. Case finding 70%, cure rate 75%
D. Case finding 70%, cure rate 85% (Correct Answer)

Explanation: ### Explanation The **Directly Observed Treatment, Short-course (DOTS)** strategy, launched by the WHO in the 1990s and adopted by India’s Revised National Tuberculosis Control Programme (RNTCP), established specific global targets to ensure effective TB control. **1. Why Option D is Correct:** The global targets set for DOTS were specifically designed to break the chain of transmission. * **Case Finding (70%):** The goal was to detect at least 70% of the estimated new sputum smear-positive cases in the community. * **Cure Rate (85%):** The goal was to achieve a cure rate of at least 85% among those detected. Mathematical modeling suggests that achieving these two specific benchmarks simultaneously leads to a significant decline in the prevalence and incidence of Tuberculosis. **2. Why Other Options are Incorrect:** * **Options A & B:** These overestimate the initial case-finding target. While higher detection is always desirable, the official DOTS benchmark was set at 70%. * **Option C:** This underestimates the cure rate. A cure rate of 75% is insufficient to prevent the emergence of Multi-Drug Resistant TB (MDR-TB) and does not adequately reduce the pool of infectious patients. **3. High-Yield Clinical Pearls for NEET-PG:** * **Evolution of Targets:** Under the current **National Strategic Plan (2017-2025)** and the **Nikshay** ecosystem, India has moved beyond these 70/85 targets toward "Elimination" (defined as <1 case per million population). * **DOTS Five Pillars:** 1. Political commitment, 2. Good quality microscopy (Diagnosis), 3. Uninterrupted supply of drugs, 4. Direct observation of treatment, 5. Systematic recording and reporting. * **Success Indicator:** The most sensitive indicator of the success of the RNTCP/NTEP is the **Cure Rate**.

Question 398: Which of the following is NOT a primordial prevention strategy?

A. Exercise
B. Good nutrition
C. No smoking
D. Screening for hypertension (Correct Answer)

Explanation: **Explanation:** The core concept of **Primordial Prevention** is the prevention of the emergence or development of risk factors in population groups where they have not yet appeared. It targets the social, economic, and environmental patterns of living (underlying conditions) that are known to contribute to an elevated risk of disease. **Why Option D is the Correct Answer:** **Screening for hypertension** is a classic example of **Secondary Prevention**. Secondary prevention aims to detect a disease in its early, asymptomatic stage (early diagnosis) and initiate prompt treatment to prevent complications. Since hypertension is already a "risk factor" that has developed in the individual, screening for it occurs after the primordial stage has passed. **Analysis of Incorrect Options:** * **A, B, and C (Exercise, Good nutrition, No smoking):** These are quintessential primordial prevention strategies. They focus on establishing healthy lifestyle patterns in children and young adults to ensure that risk factors like obesity, dyslipidemia, and tobacco addiction never develop in the first place. **High-Yield NEET-PG Pearls:** 1. **Primordial vs. Primary:** Primordial prevention prevents the *emergence* of risk factors (e.g., teaching children to avoid junk food). Primary prevention acts when a risk factor is *present* but the disease hasn't started (e.g., using a statin for high cholesterol to prevent an MI). 2. **Target Audience:** Primordial prevention is most effective when targeted at children and adolescents to discourage the adoption of harmful lifestyles. 3. **Modes of Intervention:** Primordial prevention is achieved through individual and mass education. 4. **Levels of Prevention Hierarchy:** * **Primordial:** Prevent risk factor development. * **Primary:** Action before the onset of disease (Health promotion & Specific protection). * **Secondary:** Early diagnosis and prompt treatment. * **Tertiary:** Disability limitation and Rehabilitation.

Question 399: Which of the following is NOT included in the history of present illness (HPI)?

A. Adult literacy rate
B. Percentage of the population lacking a water source
C. Probability of not surviving to age 100 at birth (Correct Answer)
D. Percentage of children underweight for their age

Explanation: ### Explanation The **Human Poverty Index (HPI)** was introduced by the UNDP in 1997 to measure deprivation in three fundamental dimensions of human life: longevity, knowledge, and a decent standard of living. **1. Why Option C is Correct:** The longevity component of HPI is measured by the **probability of not surviving to age 40** (for HPI-1, used in developing countries) or **age 60** (for HPI-2, used in developed countries). There is no standard health index that utilizes "probability of not surviving to age 100" as a core metric. Therefore, Option C is the outlier. **2. Analysis of Incorrect Options:** * **Option A (Adult Literacy Rate):** This represents the **Knowledge** dimension of the HPI. It measures the percentage of adults who can read and write, reflecting educational deprivation. * **Option B (Water Source) & Option D (Underweight Children):** These represent the **Decent Standard of Living** dimension. This is measured by a composite of three variables: the percentage of people without access to safe water, the percentage without access to health services, and the percentage of underweight children under five. **3. NEET-PG High-Yield Pearls:** * **HPI-1 vs. HPI-2:** HPI-1 (Developing countries) uses survival to age 40; HPI-2 (Developed countries) uses survival to age 60 and includes a fourth dimension: **Social Exclusion** (measured by long-term unemployment). * **Evolution of Indices:** In 2010, the HPI was replaced by the **Multidimensional Poverty Index (MPI)** in the Human Development Reports. * **MPI Dimensions:** Health (Nutrition, Child Mortality), Education (Years of schooling, Enrollment), and Standard of Living (Cooking fuel, Sanitation, Water, Electricity, Floor, Assets). * **PQLI vs. HDI:** Remember that PQLI (Physical Quality of Life Index) includes Infant Mortality Rate and Life Expectancy at Age 1, while HDI (Human Development Index) uses Life Expectancy at Birth.

Question 400: What does the quarantine period represent?

A. Median incubation period
B. Period of communicability
C. Maximum incubation period (Correct Answer)
D. Minimum incubation period

Explanation: **Explanation:** **1. Why Option C is Correct:** Quarantine is the limitation of movement of healthy persons (or domestic animals) who have been exposed to a communicable disease for a duration equal to the **maximum incubation period** of that specific disease. The objective is to prevent the transmission of the disease during the stage when the individual might be subclinically infected but not yet symptomatic. By staying in quarantine for the maximum possible incubation period, we ensure that if the person does not develop symptoms by the end of this timeframe, they are effectively "cleared" and not a risk to the community. **2. Why Other Options are Incorrect:** * **Median Incubation Period (A):** This is the time by which 50% of infected individuals develop symptoms. Using this for quarantine would fail to catch the other 50% who develop the disease later. * **Period of Communicability (B):** This refers to the time during which an infectious agent may be transferred from an infected person to another. This defines the duration of **Isolation** (for sick individuals), not Quarantine (for healthy contacts). * **Minimum Incubation Period (D):** This is the shortest time after exposure that symptoms appear. Using this would be ineffective as most cases develop symptoms after this point. **3. NEET-PG High-Yield Pearls:** * **Quarantine vs. Isolation:** Quarantine is for **healthy/exposed** contacts; Isolation is for **sick/infected** cases. * **Types of Quarantine:** * *Absolute:* Complete limitation of movement. * *Modified:* Partial restriction (e.g., excluding children from school). * **International Health Regulations (IHR):** Currently, formal international quarantine is primarily applied to three diseases: **Plague, Cholera, and Yellow Fever.** * **Concept Origin:** The word comes from "Quaranta," meaning 40 days (historically used for ships arriving in Venice).

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