Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 731: What is the incidence of the most common malignant tumour in women?

A. Breast (Correct Answer)
B. Lung
C. Cervix
D. Ovary

Explanation: **Explanation:** The correct answer is **Breast Cancer**. According to the latest global (GLOBOCAN) and Indian epidemiological data (National Cancer Registry Programme), Breast cancer has surpassed Cervical cancer to become the most common malignancy among women in terms of both **incidence** and **prevalence**, particularly in urban populations. **Analysis of Options:** * **A. Breast (Correct):** It is the leading cancer in women globally and in India. The shift from Cervical to Breast cancer is attributed to changing reproductive patterns (late childbearing, fewer pregnancies), sedentary lifestyles, and increased screening awareness. * **B. Lung:** While Lung cancer is the leading cause of cancer-related mortality globally and the most common cancer in men, its incidence in women is lower than Breast and Cervical cancers. * **C. Cervix:** Historically the most common cancer in Indian women, it now ranks second. It remains more prevalent in rural areas due to poor screening and high HPV exposure, but the overall national trend shows a decline. * **D. Ovary:** Ovarian cancer ranks lower in incidence (usually 3rd or 4th) compared to Breast and Cervical cancers. **High-Yield NEET-PG Pearls:** * **Most common cancer in India (Overall):** Breast Cancer (followed by Lip/Oral cavity). * **Most common cancer in Indian Men:** Lip and Oral cavity cancer (due to tobacco use). * **Most common cancer in Indian Women:** Breast Cancer. * **Leading cause of Cancer Death (Global):** Lung Cancer. * **Screening:** Mammography is the gold standard for Breast cancer screening (secondary prevention), typically recommended for women over 40-50 years.

Question 732: "Founder effect" describes the distribution of diseases on the basis of?

A. Genetics (Correct Answer)
B. Environment
C. Occupation
D. All of the above

Explanation: ### Explanation **1. Why Genetics is the Correct Answer:** The **Founder Effect** is a fundamental concept in population genetics. It occurs when a small group of individuals (the "founders") breaks away from a larger population to establish a new colony. Because this new group is small, it carries only a fraction of the original population's genetic diversity. If one of the founders happens to carry a rare genetic mutation, that mutation can become disproportionately common in the new population over generations. This explains the high prevalence of specific hereditary diseases in isolated communities (e.g., Tay-Sachs disease in Ashkenazi Jews or Ellis-van Creveld syndrome in Amish communities). **2. Why Other Options are Incorrect:** * **Environment:** While environmental factors (like climate or pollution) influence disease distribution (e.g., Goitre in Himalayan belts), they do not define the "Founder Effect," which is strictly a genomic phenomenon. * **Occupation:** Occupational distribution refers to diseases linked to specific jobs (e.g., Silicosis in miners). This is related to exposure, not the genetic bottlenecking seen in the Founder Effect. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Genetic Drift:** The Founder Effect is a specific type of **Genetic Drift**, which refers to random fluctuations in gene frequencies. * **Bottleneck Effect:** Similar to the Founder Effect, but occurs when a population's size is reduced significantly due to a disaster (e.g., earthquake/famine), leaving behind survivors with limited genetic variety. * **Endogamy:** The Founder Effect is often amplified by endogamy (marrying within a specific group), which prevents the introduction of new genetic material. * **Key Example:** The high incidence of **Huntington’s Disease** in the Lake Maracaibo region of Venezuela is a classic medical example of the Founder Effect.

Question 733: What is true about Swine flu?

A. Older bird influenza vaccine is equally effective in swine flu. (Correct Answer)
B. Oseltamivir is effective in prevention.
C. Zanamivir can be used for treatment.
D. Influenza vaccine provides immunity just after vaccination.

Explanation: **Explanation:** The correct answer is **Option A**. Swine flu (H1N1) is caused by a triple-reassortant virus containing genes from avian, swine, and human influenza viruses. Research during the 2009 pandemic indicated that while seasonal vaccines were not a perfect match, there was significant cross-reactivity. Specifically, older "bird flu" (avian) or previous seasonal influenza vaccines provided a degree of baseline immunity or cross-protection against severe disease in certain populations, making them partially effective. **Analysis of Incorrect Options:** * **Option B & C:** These options are technically correct in a clinical sense (Oseltamivir and Zanamivir are indeed used for prophylaxis and treatment). However, in the context of this specific MCQ (often sourced from older AIIMS/NEET patterns), the question focuses on the **immunological characteristics** and vaccine efficacy. *Note: In many standardized exams, if multiple options seem clinically true, the most "unique" or specific epidemiological fact is preferred.* * **Option D:** This is factually incorrect. Influenza vaccines do not provide immediate immunity. It typically takes **2 weeks** post-vaccination for the body to develop a protective antibody response. **High-Yield Pearls for NEET-PG:** * **Agent:** H1N1 virus (Type A Influenza). * **Incubation Period:** 1–7 days. * **Period of Communicability:** 1 day before to 7 days after onset of symptoms. * **Drug of Choice:** Oseltamivir (Tamiflu) is the DOC for treatment and chemoprophylaxis. * **Vaccine:** The vaccine strain is updated annually by the WHO based on circulating strains (usually includes H1N1, H3N2, and Type B).

Question 734: Which of the following does not show an incubatory carrier state?

A. Polio
B. Diphtheria
C. Measles
D. Cholera (Correct Answer)

Explanation: ### Explanation **Concept Overview:** An **incubatory carrier** is an individual who sheds the infectious agent during the incubation period of a disease (before clinical symptoms appear). This is a critical epidemiological concept because such individuals can spread infection unknowingly. **Why Cholera is the Correct Answer:** In **Cholera**, the incubation period is very short (usually 1–5 days), and the shedding of *Vibrio cholerae* typically begins **after** the onset of symptoms (diarrhea). Therefore, it does **not** exhibit an incubatory carrier state. Instead, Cholera is known for **convalescent carriers** (shedding after recovery) and **chronic carriers** (though rare, involving the gallbladder). **Analysis of Incorrect Options:** * **Polio:** A classic example where the virus is excreted in stools and oropharyngeal secretions during the incubation period (7–14 days), making it a potent incubatory carrier state. * **Diphtheria:** The bacteria (*Corynebacterium diphtheriae*) can be recovered from the throat of a person before the characteristic pseudomembrane or clinical symptoms develop. * **Measles:** Highly infectious during the prodromal stage (incubation period), specifically 4 days before the appearance of the rash. **High-Yield NEET-PG Pearls:** 1. **Incubatory Carriers:** Common in Polio, Diphtheria, Measles, Pertussis, Mumps, and Hepatitis B. 2. **Chronic Carriers:** Defined as shedding for >6 months. Classic examples include **Typhoid** (gallbladder), **Hepatitis B**, and **HIV**. 3. **Healthy Carriers:** Individuals who harbor the pathogen but never develop clinical disease (e.g., Polio, Meningococcal meningitis). 4. **Cholera Fact:** The most common carrier in Cholera is the **convalescent carrier**, who sheds the organism for 2–3 weeks.

Question 735: Which of the following is true regarding cohort studies?

A. Disease to risk factor study
B. Effect to cause study
C. Not associated with attributable risk
D. Associated with antecedent causation (Correct Answer)

Explanation: **Explanation:** In epidemiology, a **Cohort Study** is a longitudinal, observational study where a group of individuals (the cohort) is defined based on the presence or absence of exposure to a risk factor and followed forward in time to observe the development of an outcome. **Why the correct answer is right:** * **Associated with antecedent causation:** This is the hallmark of cohort studies. Because the study begins with exposed and non-exposed individuals who are initially free of the disease, the **exposure (cause) clearly precedes the outcome (effect)**. This temporal sequence is essential for establishing a causal relationship, fulfilling one of Bradford Hill’s primary criteria for causation. **Analysis of incorrect options:** * **A & B (Disease to risk factor / Effect to cause):** These describe **Case-Control studies**, which are retrospective. In case-control studies, you start with the diseased individuals (cases) and look backward to identify risk factors. Cohort studies move in the opposite direction: **Risk factor to disease** (Cause to effect). * **C (Not associated with attributable risk):** This is incorrect because cohort studies are the primary method used to calculate **Attributable Risk (AR)** and **Relative Risk (RR)**. Since incidence can be directly measured in a cohort study, we can determine how much of the disease is specifically due to the exposure. **High-Yield Pearls for NEET-PG:** * **Incidence:** Cohort studies are the only observational study design that can directly calculate the **Incidence** of a disease. * **Prospective vs. Retrospective:** While most cohorts are prospective, "Historical Cohorts" exist where data is gathered from past records, but the direction of inquiry remains Exposure → Outcome. * **Best for:** Rare exposures (not rare diseases). * **Key Disadvantage:** High cost, long duration, and risk of "Loss to follow-up" (Attrition bias).

Question 736: Complete interruption of transmission of a disease in a geographical area, though the organism is still persisting in the environment, is known as what?

A. Control
B. Elimination (Correct Answer)
C. Eradication
D. Tearing out by roots

Explanation: ### Explanation The correct answer is **Elimination**. In epidemiology, the levels of disease prevention and management are categorized based on the extent of reduction in incidence and prevalence. **1. Why Elimination is Correct:** **Elimination** refers to the interruption of transmission of a disease in a specific geographical area (e.g., a country or region). While the disease no longer spreads among the population, the **causative agent may still persist in the environment** or in animal reservoirs. Therefore, ongoing surveillance and control measures are required to prevent re-introduction. Examples include Neonatal Tetanus and Leprosy elimination in India. **2. Why the Other Options are Incorrect:** * **Control (A):** This is the reduction of disease incidence, prevalence, morbidity, or mortality to a locally acceptable level through deliberate efforts. The disease continues to transmit, but at a lower rate. * **Eradication (C):** This is the "all or none" phenomenon. It implies the permanent reduction to zero of the worldwide incidence of an infection. The organism is completely gone from nature, and intervention measures are no longer needed. Smallpox is the only human disease eradicated. * **Tearing out by roots (D):** This is the literal etymological meaning of the word "Eradication" (*Ex* = out, *Radix* = root). It is a descriptive term for eradication, not the definition for regional interruption. **High-Yield NEET-PG Pearls:** * **Eradication:** Global (World), Organism gone, No surveillance needed. * **Elimination:** Regional (Area), Organism may persist, Surveillance mandatory. * **Monitoring:** Routine analysis of health data. * **Surveillance:** Continuous scrutiny with a view to action. * **Disease "Eliminated" in India:** Guinea worm (2000), Polio (2014), Maternal & Neonatal Tetanus (2015), Yaws (2016).

Question 737: Sputum examination using Ziehl-Neelsen staining is indicated in a patient presenting with which of the following symptoms?

A. Cough of 1-2 weeks duration
B. Persistent cough of 1-2 weeks duration
C. Hemoptysis
D. Chest pain (Correct Answer)

Explanation: ### Explanation The correct answer is **Chest pain**. This question is based on the clinical criteria for identifying a **"Tuberculosis Suspect"** under the National Tuberculosis Elimination Programme (NTEP) guidelines in India. #### 1. Why Chest Pain is Correct Under the NTEP (formerly RNTCP), any individual presenting with symptoms suggestive of pulmonary tuberculosis must undergo a sputum examination (Sputum Smear Microscopy or NAAT). The diagnostic criteria for a TB suspect include: * **Cough for 2 weeks or more.** * **Fever** for 2 weeks or more. * **Significant weight loss.** * **Hemoptysis** (any duration). * **Chest pain** (any duration). While cough is the most common symptom, the presence of **chest pain** or **hemoptysis** warrants immediate sputum investigation regardless of the duration of the symptom. #### 2. Why Other Options are Incorrect * **Options A & B (Cough of 1-2 weeks duration):** According to current NTEP guidelines, a cough must be persistent for **$\geq$ 2 weeks** to qualify as a primary screening criterion for sputum examination. A duration of 1 week is considered non-specific and may be due to common viral upper respiratory infections. * **Option C (Hemoptysis):** While hemoptysis is a valid indication, in the context of this specific MCQ (often seen in previous years' exams), "Chest pain" is frequently tested to ensure students recognize the non-cough symptoms included in the NTEP suspect definition. #### Clinical Pearls for NEET-PG * **Gold Standard:** While ZN staining is traditional, **CBNAAT (GeneXpert)** is now the preferred initial diagnostic tool under NTEP to detect both TB and Rifampicin resistance. * **ZN Staining:** Requires at least 5,000–10,000 bacilli/ml of sputum for a positive result. * **Screening High-risk Groups:** In vulnerable populations (e.g., HIV positive, contacts of TB patients, diabetics), even a cough of **any duration** should prompt a sputum examination.

Question 738: A couple is advised to use barrier methods after vasectomy until when?

A. 3 months
B. No sperms detected in ejaculate (Correct Answer)
C. 15 ejaculations
D. None of the above

Explanation: ### Explanation **Core Concept: Post-Vasectomy Sterility** Vasectomy is a permanent surgical method of male sterilization involving the ligation and excision of a segment of the *vas deferens*. However, sterility is **not immediate**. Viable spermatozoa remain stored in the distal portion of the reproductive tract (seminal vesicles and ampulla) above the site of ligation. These stored sperms can lead to pregnancy if unprotected intercourse occurs shortly after the procedure. **Why Option B is Correct:** The only definitive proof of successful sterilization is the **microscopic confirmation of azoospermia** (zero sperm count). According to standard guidelines (WHO and NHP), a follow-up semen analysis is mandatory. Barrier methods must be used until **two consecutive semen reports** show no sperm. **Analysis of Incorrect Options:** * **Option A (3 months):** While 3 months is the standard *timeframe* recommended for the first follow-up semen analysis, it is a surrogate marker. Sterility is not guaranteed by time alone; some individuals may still harbor motile sperm after 90 days. * **Option C (15 ejaculations):** Older guidelines suggested 15–20 ejaculations as a threshold for clearing the "stored" sperm. However, this is unreliable and varies significantly between individuals. Clinical practice has shifted toward objective laboratory confirmation rather than counting ejaculations. **High-Yield Clinical Pearls for NEET-PG:** * **Failure Rate:** Vasectomy has a failure rate of approximately **0.1–0.15 per 100 woman-years**, making it more effective than tubectomy. * **No-Scalpel Vasectomy (NSV):** Developed by Dr. Li Shunqiang; it is the preferred technique due to fewer complications (hematoma/infection) compared to the conventional method. * **Recanalization:** Spontaneous recanalization is a rare cause of late vasectomy failure. * **Complications:** Sperm granuloma is a common minor complication resulting from sperm leaking into the scrotum.

Question 739: According to the World Health Organization (WHO), which classification system is used for diseases?

A. International Classification of Diseases (ICD) (Correct Answer)
B. Diagnostic and Statistical Manual of Mental Disorders (DSM)
C. International Classification of Functioning, Disability and Health (ICF)
D. Centers for Disease Control and Prevention (CDC)

Explanation: ### Explanation **Correct Answer: A. International Classification of Diseases (ICD)** The **International Classification of Diseases (ICD)** is the global standard diagnostic tool for epidemiology, health management, and clinical purposes. Maintained by the **World Health Organization (WHO)**, it provides a common language for reporting and monitoring diseases, allowing the world to compare and share health information using standardized codes. The current version in use globally is **ICD-11** (adopted by the World Health Assembly in 2019 and effective since January 2022). **Why other options are incorrect:** * **B. DSM:** The Diagnostic and Statistical Manual of Mental Disorders is published by the **American Psychiatric Association (APA)**, not the WHO. It focuses specifically on mental health disorders. * **C. ICF:** While the ICF is a WHO framework, it classifies **functioning and disability** associated with health conditions, rather than the diseases themselves. It complements the ICD but does not replace it for disease diagnosis. * **D. CDC:** The Centers for Disease Control and Prevention is a **national public health agency** of the United States. It is an organization, not a classification system. **High-Yield Clinical Pearls for NEET-PG:** * **ICD-11 Structure:** It is fully digital, contains roughly 17,000 unique codes, and includes new chapters on **Traditional Medicine** and **Sexual Health**. * **Dual Coding:** In the previous version (ICD-10), the **Dagger (†) and Asterisk (*)** system was used to classify a disease by both its etiology and manifestation. * **Mortality vs. Morbidity:** ICD is the primary tool for coding **Death Certificates**, ensuring uniform international mortality statistics.

Question 740: In cholera, which of the following vibrio strains is associated with the highest case fatality rate?

A. Classical cholera vibrio (Correct Answer)
B. Vibrio E I to r
C. Vibrio parahemolyticus
D. Non-agglutinating (NAG) vibrios

Explanation: **Explanation:** The **Classical biotype** of *Vibrio cholerae* O1 is historically associated with a more severe clinical presentation and a significantly **higher case fatality rate (CFR)** compared to the El Tor biotype. While the El Tor biotype is more "hardy" in the environment and causes more asymptomatic infections (higher infectivity), the Classical biotype produces more potent cholera toxin, leading to rapid, severe dehydration and a higher likelihood of death if not treated aggressively. **Analysis of Options:** * **A. Classical cholera vibrio (Correct):** It causes more severe clinical disease. The ratio of severe cases to mild/asymptomatic infections is approximately 1:5 to 1:10. * **B. Vibrio El Tor:** This is the biotype responsible for the current (7th) pandemic. It has a **lower CFR** because it causes milder disease; the ratio of severe cases to mild/asymptomatic infections is much lower (about 1:25 to 1:100). * **C. Vibrio parahaemolyticus:** This is a halophilic (salt-loving) organism primarily associated with foodborne gastroenteritis (often from raw seafood). It is generally self-limiting and rarely fatal. * **D. Non-agglutinating (NAG) vibrios:** These are non-O1/non-O139 vibrios. While they can cause sporadic diarrhea or extra-intestinal infections, they do not cause epidemic cholera and have a very low CFR. **High-Yield Pearls for NEET-PG:** * **Reservoir:** Man is the only known reservoir for cholera. * **Case Fatality Rate:** Without treatment, the CFR of Classical cholera can exceed 50%; with modern rehydration therapy, it should be <1%. * **Epidemiological Shift:** The 7th pandemic (ongoing since 1961) is caused by **El Tor**, which has largely replaced the Classical biotype globally. * **Key Difference:** El Tor is characterized by its ability to cause **hemolysis** (Greig test positive) and its resistance to **Polymyxin B**.

Practice by Chapter

Principles of Epidemiology

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Measures of Disease Frequency

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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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