Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 671: The performance of components of the Physical Quality of Life Index (PQLI) is typically measured on which scale?

A. −1 to +1
B. 0 to 1
C. 0 to 100 (Correct Answer)
D. None of the above

Explanation: ### Explanation The **Physical Quality of Life Index (PQLI)** is a composite indicator developed by Morris David Morris to measure the quality of life or social well-being of a population. Unlike the Human Development Index (HDI), which includes economic factors (GNP), the PQLI focuses purely on social and demographic outcomes. **Why 0 to 100 is Correct:** The PQLI is calculated based on three indicators: **Infant Mortality Rate (IMR)**, **Life Expectancy at Age 1**, and **Basic Literacy**. For each component, the performance is placed on a scale of **0 to 100**, where 0 represents the "worst" possible performance and 100 represents the "best." The final PQLI is the arithmetic average of these three scaled scores, also resulting in a final value between 0 and 100. **Analysis of Incorrect Options:** * **Option A (-1 to +1):** This scale is typically used for **Correlation Coefficients (r)**, where +1 is a perfect positive correlation and -1 is a perfect negative correlation. * **Option B (0 to 1):** This is the scale used for the **Human Development Index (HDI)**. While the components are similar, the HDI normalizes values between 0 and 1. **High-Yield Facts for NEET-PG:** * **Components of PQLI:** Remember the mnemonic **"LIL"** (Literacy, Infant mortality, Life expectancy at age 1). * **PQLI vs. HDI:** PQLI does **not** include per capita income (GNP), whereas HDI does. * **Life Expectancy:** Note that PQLI uses life expectancy at **age 1**, while HDI uses life expectancy at **birth**. * **Interpretation:** A PQLI score above 77 is considered indicative of a "good" quality of life.

Question 672: What is the attack rate?

A. Incidence of the disease (Correct Answer)
B. Prevalence of the disease
C. Severity of the disease
D. Incubation period of the disease

Explanation: ### Explanation **1. Why Option A is Correct:** The **Attack Rate** is a specific type of **Incidence Rate**, typically used during an outbreak or epidemic. It measures the frequency of new cases of a disease in a specific population at risk over a short, defined period of time. * **Formula:** (Number of new cases / Total population at risk) × 100. * Because it tracks the occurrence of *new* cases, it is fundamentally an incidence measure, though it is expressed as a percentage rather than "person-years." **2. Why Other Options are Incorrect:** * **Option B (Prevalence):** Prevalence refers to the total number of cases (old + new) existing in a population at a given point in time. Attack rate only focuses on new cases arising during the outbreak. * **Option C (Severity):** Severity is measured by the **Case Fatality Rate (CFR)** or clinical grading, not the attack rate. Attack rate measures the *spread* or *infectivity*, not how sick the patients become. * **Option D (Incubation Period):** This is the time interval between exposure to an infectious agent and the appearance of the first sign or symptom. It is a chronological measure, not a frequency rate. **3. NEET-PG High-Yield Pearls:** * **Secondary Attack Rate (SAR):** Measures the spread of a disease from a primary case to contacts within a closed group (e.g., household). It is the best indicator of **communicability** or infectiousness. * **Denominator Rule:** In the Attack Rate, the denominator includes only those **at risk**. Those already immune (through vaccination or prior infection) are excluded. * **Primary Attack Rate:** Refers to the first wave of cases derived from the common source. * **Key Distinction:** While "Incidence" is usually for long-term monitoring, "Attack Rate" is for **short-term acute outbreaks** (e.g., food poisoning).

Question 673: When hospital-based case and control groups have different disease prevalences, what bias does this lead to?

A. Hawthorne effect
B. Berksonian bias (Correct Answer)
C. Ecological fallacy
D. Interviewer bias

Explanation: **Explanation:** **1. Why Berksonian Bias is Correct:** Berksonian bias (also known as **Admission Rate Bias**) is a type of selection bias that occurs in hospital-based case-control studies. It arises because hospitalised patients have different rates of admission, disease severity, and co-morbidities compared to the general population. If the exposure of interest increases the likelihood of hospital admission, the association between the exposure and the disease will be systematically distorted. Essentially, because both the "case" and the "control" are drawn from a hospital population with different prevalence rates than the community, the observed odds ratio does not reflect the true population risk. **2. Why Incorrect Options are Wrong:** * **Hawthorne Effect:** This is a type of observation bias where study participants change their behavior simply because they know they are being studied. * **Ecological Fallacy:** This occurs when an association observed at the aggregate/population level (e.g., country-wide data) is incorrectly assumed to apply to individuals. * **Interviewer Bias:** This is a systematic error due to the interviewer’s subconscious or conscious gathering of data in a way that favors a certain outcome (e.g., probing cases more intensely than controls). **High-Yield Clinical Pearls for NEET-PG:** * **Selection Bias** occurs during the design/sampling stage; **Information Bias** occurs during the data collection stage. * To minimize Berksonian bias, researchers should ideally use **community-based controls** rather than hospital-based controls. * **Neyman Bias (Prevalence-Incidence Bias):** Occurs when cases are selected from survivors (prevalent cases) rather than new (incident) cases, often missing those who died early.

Question 674: Which of the following diseases has a carrier stage?

A. Poliomyelitis
B. Cholera
C. Pertussis
D. All of the above (Correct Answer)

Explanation: **Explanation** The concept of a **carrier** is central to epidemiology. A carrier is an infected person or animal that harbors a specific infectious agent without having clinical disease and serves as a potential source of infection for others. **Why "All of the above" is correct:** The carrier state exists in diseases where the host's immune system limits the pathogen's activity but fails to eliminate it entirely. * **Poliomyelitis:** Fecal-oral transmission is facilitated by **convalescent and healthy carriers**. In fact, for every clinical case of polio, there are hundreds of silent carriers (inapparent infections) who shed the virus in their stools. * **Cholera:** It exhibits both **convalescent carriers** (recovering patients shedding *V. cholerae*) and **chronic carriers** (individuals shedding the organism for months or years, often harboring it in the gallbladder). * **Pertussis:** While traditionally thought to have no carrier state, modern epidemiological studies have confirmed the existence of **transient asymptomatic carriers**, particularly among vaccinated adolescents and adults who can still transmit *Bordetella pertussis* to vulnerable infants. **High-Yield Clinical Pearls for NEET-PG:** * **Diseases with NO Carrier State:** Smallpox, Measles, and Pertussis (classically taught as "no carrier," though transient carriage is now recognized; however, for MCQ purposes, if "All" is an option, include it). * **Chronic Carrier Examples:** Typhoid (Gallbladder), Hepatitis B, HIV, and Cholera. * **Pseudo-carrier:** A term sometimes used for the "incubatory carrier" who sheds the pathogen during the incubation period (e.g., Measles, Mumps, Polio). * **Epidemiological Importance:** Carriers are often more dangerous than cases because they are mobile, unrecognized, and continue their normal activities, acting as a "hidden reservoir."

Question 675: Which of the following cancers have shown to be reduced by chemoprevention trials?

A. Lymphoma and Breast Cancer
B. Breast Cancer and Cancers of the aero-digestive tract (Correct Answer)
C. Lymphoma, Breast Cancer, and Cancers of the aero-digestive tract
D. Lymphoma, Pancreatic Cancer, and Cancers of the urinary bladder

Explanation: **Explanation:** **Chemoprevention** refers to the use of specific natural or synthetic chemical agents to reverse, suppress, or prevent the progression of carcinogenesis into invasive cancer. In epidemiological trials, this strategy has demonstrated significant efficacy in specific organ systems. 1. **Why Option B is Correct:** * **Breast Cancer:** Large-scale clinical trials (e.g., NSABP P-1) proved that Selective Estrogen Receptor Modulators (SERMs) like **Tamoxifen** and **Raloxifene** significantly reduce the incidence of invasive breast cancer in high-risk women. * **Aero-digestive Tract:** Trials involving **Retinoids** (Vitamin A derivatives) and **Beta-carotene** have shown success in reversing oral leukoplakia (a precancerous lesion) and reducing the risk of secondary primary tumors in the head, neck, and esophagus. 2. **Why Other Options are Incorrect:** * **Lymphoma (Options A, C, D):** There is currently no established chemopreventive agent for lymphomas. Prevention focuses more on treating underlying infections (like H. pylori for MALT lymphoma) rather than systemic chemical prophylaxis. * **Pancreatic and Urinary Bladder Cancer (Option D):** While research is ongoing (e.g., NSAIDs for bladder cancer), these have not yet shown the robust, trial-proven reduction required to be categorized alongside breast and aero-digestive cancers in standard epidemiological textbooks. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Chemoprevention:** Aimed at healthy individuals with high risk (e.g., Tamoxifen for BRCA carriers). * **Secondary Chemoprevention:** Aimed at preventing a second primary cancer in patients already treated for one. * **Key Agents:** * **Aspirin/NSAIDs:** Proven to reduce the risk of **Colorectal Cancer** (adenomatous polyps). * **Finasteride:** Studied for Prostate Cancer prevention. * **Retinoids:** Most effective for skin and aero-digestive tract lesions.

Question 676: Which of the following is an example of primary prevention?

A. Screening test
B. Early diagnosis
C. Use of mosquito net (Correct Answer)
D. Restoration of lost function

Explanation: ### Explanation **Primary prevention** aims to prevent the onset of a disease by controlling causes and risk factors. It occurs in the **pre-pathogenesis phase** of a disease (before the disease process has started). It consists of two main components: Health Promotion and Specific Protection. **Why Option C is Correct:** The **use of a mosquito net** is a classic example of **Specific Protection**. It is a targeted intervention designed to prevent the host from coming into contact with the vector (mosquito), thereby preventing the initiation of diseases like Malaria, Filariasis, or Dengue. Since the intervention is applied to a healthy individual to prevent the disease from occurring, it falls under primary prevention. **Analysis of Incorrect Options:** * **Options A & B (Screening and Early Diagnosis):** These are examples of **Secondary Prevention**. Secondary prevention aims to halt the progress of a disease in its early stages and prevent complications. It occurs during the **early pathogenesis phase**. The hallmark of secondary prevention is "Early Diagnosis and Treatment." * **Option D (Restoration of lost function):** This is an example of **Tertiary Prevention**. It involves **Rehabilitation** (medical, vocational, or social) to restore a patient to an optimal level of functioning after a disease has caused permanent damage or disability. **High-Yield Clinical Pearls for NEET-PG:** * **Primordial Prevention:** Prevention of the *emergence* of risk factors (e.g., discouraging children from starting smoking). * **Primary Prevention:** Action taken *before* the onset of disease (e.g., Immunization, Vitamin A prophylaxis). * **Secondary Prevention:** Action taken *after* the disease has started but before irreversible damage (e.g., Pap smear, Sputum microscopy for TB). * **Tertiary Prevention:** Action taken to reduce disability (e.g., Physiotherapy in Polio, Crutches for amputees).

Question 677: Which disease is currently under WHO surveillance?

A. Rabies (Correct Answer)
B. Mumps
C. Hepatitis
D. Tetanus

Explanation: ### Explanation **Correct Answer: A. Rabies** The World Health Organization (WHO) maintains a global surveillance system for specific diseases that pose a significant public health threat. **Rabies** is currently under WHO surveillance because it is a 100% fatal but 100% vaccine-preventable zoonotic disease. It is part of the "Zero by 30" global strategic plan to end human deaths from dog-mediated rabies by 2030. Surveillance is critical for monitoring the burden of disease, identifying hotspots, and evaluating the effectiveness of mass dog vaccination programs. **Analysis of Incorrect Options:** * **B. Mumps:** While mumps is a common childhood illness and part of national immunization programs (like MMR), it is not currently listed under the primary global WHO surveillance priority list compared to high-mortality or epidemic-prone diseases. * **C. Hepatitis:** While WHO monitors Viral Hepatitis (A, B, C, D, E) through global progress reports and elimination targets, it is generally managed through specific global health strategies rather than the core "International Health Regulations (IHR)" surveillance list in the same context as Rabies. * **D. Tetanus:** Maternal and Neonatal Tetanus (MNT) elimination is a global goal, but Tetanus is not a "notifiable" disease under international surveillance in the same manner as Rabies, as it is not communicable between humans. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Surveillance List:** Diseases currently under surveillance include **Rabies, Influenza, Malaria, Tuberculosis, HIV/AIDS, and Onchocerciasis.** * **IHR (2005):** Under the International Health Regulations, three diseases must be notified to WHO regardless of the context: **Smallpox, Poliomyelitis (wild-type), and Human Influenza caused by a new subtype.** * **Rabies Incubation:** Usually 1–3 months but can range from <1 week to >1 year. * **Rule of 10:** In Rabies, the biting animal (dog/cat) is observed for 10 days; if it remains healthy, the person is safe.

Question 678: Who is regarded as the father of public health?

A. Louis Pasteur
B. None of the above (Correct Answer)
C. John Snow
D. Robert Koch

Explanation: ### Explanation The correct answer is **None of the above** because the title "Father of Public Health" is traditionally attributed to **Cholera**. This is a unique historical concept in epidemiology where a disease, rather than a person, is credited with the birth of public health. The devastating cholera epidemics of the 19th century in London forced the government to recognize the link between environment, sanitation, and health, leading to the Public Health Act of 1848. **Analysis of Options:** * **Louis Pasteur:** Known as the **Father of Microbiology**. He proposed the Germ Theory of Disease and developed vaccines for rabies and anthrax. * **John Snow:** Regarded as the **Father of Modern Epidemiology**. He famously traced the 1854 London cholera outbreak to the Broad Street pump, demonstrating the importance of descriptive epidemiology. * **Robert Koch:** Known as the **Father of Bacteriology**. He discovered the causative agents of Anthrax, Tuberculosis, and Cholera, and formulated Koch’s Postulates. **High-Yield Clinical Pearls for NEET-PG:** * **Father of Public Health:** Cholera. * **Father of Medicine:** Hippocrates (first to associate disease with environmental factors rather than supernatural causes). * **Father of Vaccination/Immunology:** Edward Jenner. * **Father of Evidence-Based Medicine:** David Sackett. * **First Epidemiologist:** Hippocrates. * **The "Great Sanitary Awakening":** Occurred in the mid-19th century in London, marking the beginning of the modern public health movement.

Question 679: Which type of study is best suited for investigating risk factors associated with multiple diseases?

A. Cohort study (Correct Answer)
B. Case control study
C. Ecological study
D. Clinical trial

Explanation: **Explanation:** The correct answer is **Cohort Study**. In a cohort study, a group of disease-free individuals is classified based on their exposure status and followed forward in time to observe the development of outcomes. Because the study starts with an exposure and monitors for any subsequent health events, it allows researchers to study **multiple outcomes (diseases)** resulting from a single exposure (e.g., studying smoking and its link to lung cancer, heart disease, and stroke simultaneously). **Why other options are incorrect:** * **Case-Control Study:** These start with the disease (outcome) and look backward for exposures. They are ideal for studying **multiple exposures** for a single disease, but not multiple diseases. * **Ecological Study:** These use populations or groups as the unit of study rather than individuals. They are used for generating hypotheses but cannot establish individual-level associations. * **Clinical Trial:** These are interventional studies designed to test the efficacy of a drug or procedure, not primarily for investigating a wide range of risk factors for multiple diseases. **High-Yield Clinical Pearls for NEET-PG:** * **Cohort Study:** Best for rare exposures; can calculate **Incidence** and **Relative Risk (RR)**. * **Case-Control Study:** Best for rare diseases; can calculate **Odds Ratio (OR)**. * **Mnemonic:** * **C**ohort = Multiple Outcomes (**O**). * **C**ase-Control = Multiple Exposures (**E**). * **Incidence** can only be directly calculated in a Cohort study because it provides a denominator of "population at risk" over time.

Question 680: Which vaccine is contraindicated in a person undergoing intensive chemotherapy?

A. MMR (Correct Answer)
B. Hepatitis B
C. Pneumococcus
D. DPT

Explanation: **Explanation:** The core principle in vaccinating immunocompromised patients is the distinction between **Live Attenuated Vaccines** and **Inactivated/Killed Vaccines**. **1. Why MMR is the Correct Answer:** MMR (Measles, Mumps, and Rubella) is a **live attenuated vaccine**. In patients undergoing intensive chemotherapy, the immune system is severely suppressed (neutropenia and lymphopenia). In such individuals, the attenuated virus in the vaccine can replicate unchecked, leading to a severe, disseminated, and potentially fatal infection instead of providing immunity. Therefore, all live vaccines are strictly contraindicated during active chemotherapy. **2. Why the Other Options are Incorrect:** * **Hepatitis B:** This is a **subunit (recombinant)** vaccine. It contains only a portion of the virus (HBsAg) and cannot cause disease. * **Pneumococcus:** This is a **polysaccharide or conjugate** vaccine. It contains killed bacterial components. * **DPT:** This is a combination of **toxoids** (Diphtheria and Tetanus) and **killed/acellular** components (Pertussis). * *Note:* While these inactivated vaccines are "safe" to administer, their efficacy is often reduced in chemotherapy patients due to a poor antibody response. **3. NEET-PG High-Yield Pearls:** * **Live Vaccines (Mnemonic: "BOY REY MEETS CRIME"):** BCG, OPV, Yellow Fever, Rotavirus, Epidemic Typhus, MMR, Endemic Typhus, Typhoid (Ty21a), Chickenpox (Varicella), Rubella, Influenza (Intranasal), Measles. * **Timing:** Live vaccines should ideally be administered at least **4 weeks before** starting chemotherapy or **3–6 months after** chemotherapy has ended. * **Exception:** In HIV patients, MMR can be given if the CD4 count is >15% or >200 cells/mm³, but **BCG is strictly contraindicated** in symptomatic HIV. * **Household Contacts:** It is safe for household members of a chemo patient to receive most live vaccines (like MMR), but **OPV** should be avoided to prevent vaccine-derived paralytic polio transmission; IPV is preferred.

Practice by Chapter

Principles of Epidemiology

Practice Questions

Measures of Disease Frequency

Practice Questions

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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