Epidemiology — MCQs
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Recall bias is most commonly associated with which study design?
Breteau index is used for which of the following?
Which of the following vaccines is administered at birth?
Which disinfectant is commonly used for blood spills?
Which of the following diseases is transmitted via the fecal-oral route?
What is considered the heart of a controlled trial?
Dengue fever is transmitted by which type of mosquito?
What is the incubation period of Haemophilus influenzae?
What is a migration study used to investigate?
Surveillance is necessary for all the following diseases recommended by WHO except?
Epidemiology Indian Medical PG Practice Questions and MCQs
Question 1151: Recall bias is most commonly associated with which study design?
- A. Cohort study
- B. Case control study (Correct Answer)
- C. Cross-sectional study
- D. Randomized controlled trial
Explanation: **Explanation:** **Recall bias** is a systematic error that occurs when participants do not remember past events or experiences accurately or omit details. It is most commonly associated with **Case-Control studies** because these studies are inherently **retrospective**. In this design, researchers start with the outcome (cases) and look backward in time to assess exposure. Patients with a specific disease (cases) are often more motivated to search their memories for potential causes or "triggers" compared to healthy individuals (controls), leading to a differential quality of reporting between the two groups. **Analysis of Incorrect Options:** * **Cohort Study:** These are primarily prospective. Exposure is measured at the start, and participants are followed forward in time. Since data on exposure is collected *before* the outcome occurs, recall bias is minimized. * **Cross-sectional Study:** These measure prevalence at a single point in time. While they can suffer from recall bias if asking about past events, the primary bias associated with them is **Neyman bias (Late-look bias)**. * **Randomized Controlled Trial (RCT):** These are experimental and prospective. Since researchers control the intervention and monitor outcomes in real-time, recall bias is virtually non-existent. **NEET-PG High-Yield Pearls:** * **Definition:** Recall bias is a type of **Information/Observation Bias**. * **Prevention:** Can be minimized by using objective records (medical files), blinding the participants to the study hypothesis, or using diseased controls. * **Memory vs. Recall Bias:** Simple forgetting is "non-differential" and leads to underestimation of effect; "Recall Bias" is differential and leads to overestimation of the association.
Question 1152: Breteau index is used for which of the following?
- A. Aedes (Correct Answer)
- B. Anopheles
- C. Hookworm infection
- D. Hard tick
Explanation: **Explanation:** The **Breteau Index (BI)** is a key entomological indicator used in the surveillance of **Aedes aegypti** mosquitoes, the primary vector for Dengue, Chikungunya, and Zika virus. It is defined as the **number of positive containers (breeding sites) per 100 houses inspected**. It is considered the most sensitive of the larval indices for predicting outbreaks because it establishes a relationship between the number of positive containers and the number of houses. **Analysis of Options:** * **A. Aedes (Correct):** Along with the House Index (percentage of houses positive for larvae) and Container Index (percentage of containers positive for larvae), the Breteau Index is used to monitor Aedes populations and evaluate the effectiveness of vector control programs. * **B. Anopheles:** Surveillance for Anopheles (Malaria vector) typically uses the **Spleen Index**, **Annual Parasite Index (API)**, or **Man-Hour Rate** (for adult mosquitoes), rather than larval container indices. * **C. Hookworm infection:** This is monitored using the **Prevalence Rate** or **Intensity of Infection** (measured via eggs per gram of feces using the Kato-Katz technique). * **D. Hard tick:** Tick populations are usually monitored through "tick dragging" or "flagging" methods to determine density, not through container-based larval indices. **High-Yield Clinical Pearls for NEET-PG:** * **Aedes Indices Thresholds:** A Breteau Index **>20** or a House Index **>5%** indicates a high risk of Dengue transmission in a community. * **Aedes Characteristics:** Known as "Day biters" and "Tiger mosquitoes," they breed in clean, stagnant water (artificial containers, tires, flower pots). * **Stegomyia Index:** This is an older term for the House Index.
Question 1153: Which of the following vaccines is administered at birth?
- A. DPT
- B. OPV (Correct Answer)
- C. Measles
- D. TAB
Explanation: **Explanation:** According to the **National Immunization Schedule (NIS)** in India, the vaccines administered at birth (the "birth dose") are **BCG, Hepatitis B, and OPV (Zero dose)**. **Why OPV is correct:** The **Oral Polio Vaccine (OPV) Zero dose** is given at birth to ensure early intestinal immunity and to prevent the establishment of the polio virus in the gut. It is called "Zero dose" because it is administered before the primary series (which starts at 6 weeks) and is not counted toward the three-dose primary schedule. **Analysis of Incorrect Options:** * **DPT (Diphtheria, Pertussis, Tetanus):** This is a combination vaccine traditionally started at **6 weeks** of age as part of the Pentavalent vaccine (which also includes Hep B and HiB). It is never given at birth due to the immaturity of the immune response to these specific antigens. * **Measles:** The first dose of the Measles-Rubella (MR) vaccine is administered at **9 completed months** (9-12 months). Administering it earlier is ineffective due to the presence of interfering maternal antibodies. * **TAB:** This is an older vaccine for enteric fever (Typhoid A and B). It is no longer part of the routine NIS and was never indicated for newborns. **High-Yield Clinical Pearls for NEET-PG:** 1. **BCG:** Can be given up to 1 year of age if missed at birth. 2. **Hepatitis B (Birth Dose):** Must be given within **24 hours** of birth to prevent vertical transmission. 3. **OPV Zero Dose:** Can be given up to the first **15 days** of life. 4. **Vitamin A:** The first dose (1 lakh IU) is given at 9 months along with the MR vaccine.
Question 1154: Which disinfectant is commonly used for blood spills?
- A. Phenol
- B. Glutaraldehyde
- C. Ethanol
- D. Sodium hypochlorite (Correct Answer)
Explanation: **Explanation:** **Sodium hypochlorite (Option D)** is the disinfectant of choice for blood spills because it is a potent, broad-spectrum oxidizing agent. It is highly effective against blood-borne pathogens, including Hepatitis B (HBV), Hepatitis C (HCV), and HIV. For clinical practice and NEET-PG purposes, the concentration used is critical: * **Small spills:** 1% sodium hypochlorite (1:100 dilution). * **Large spills (>10ml):** 10% sodium hypochlorite (1:10 dilution). The contact time should be at least 10–20 minutes to ensure complete disinfection. **Analysis of Incorrect Options:** * **Phenol (A):** Historically significant but now rarely used for spills due to its toxicity, corrosive nature, and poor efficacy against non-enveloped viruses. It is primarily used for floor cleaning in non-critical areas. * **Glutaraldehyde (B):** Known as "Cidex," it is a high-level disinfectant used for **cold sterilization** of heat-sensitive endoscopes and bronchoscopes. It is not used for environmental spills due to its pungent fumes and respiratory toxicity. * **Ethanol (C):** While 70% alcohol is an excellent antiseptic for skin and small surfaces (like medication vial stoppers), it evaporates too quickly to provide the necessary contact time for large blood spills and is ineffective against bacterial spores. **High-Yield Clinical Pearls for NEET-PG:** * **Spill Management Protocol:** Always pour the hypochlorite solution *around* the spill first, then over it, to prevent aerosolization. Use absorbent material (like paper towels) to clean it up after the contact time. * **HIV Inactivation:** Sodium hypochlorite inactivates HIV in less than a minute, but standard protocols require longer contact for other resistant viruses. * **Bleach Caution:** Never mix hypochlorite with acids or ammonia, as it releases toxic chlorine gas.
Question 1155: Which of the following diseases is transmitted via the fecal-oral route?
- A. Herpes simplex (Correct Answer)
- B. Leprosy
- C. Tetanus
- D. Whooping cough
Explanation: **Explanation:** The transmission of infectious diseases is a high-yield topic for NEET-PG. While **Herpes Simplex Virus (HSV)** is primarily known for transmission via direct contact with lesions or secretions (oral-to-oral or sexual), it is important to note that **HSV-1** can be shed in saliva and occasionally transmitted through contaminated objects or the **fecal-oral route**, particularly in crowded or unsanitary conditions among children. In the context of this specific question and the provided options, HSV is the only pathogen that can involve mucosal/enteric shedding, whereas the others have strictly defined non-enteric routes. **Analysis of Incorrect Options:** * **Leprosy (B):** Transmitted primarily via **prolonged close contact** through respiratory droplets (nasal secretions) from multibacillary cases. It is not an enteric infection. * **Tetanus (C):** Caused by *Clostridium tetani* spores entering the body through **contaminated wounds**, injuries, or the umbilical stump (neonatal tetanus). It is non-communicable from person to person. * **Whooping Cough (D):** Caused by *Bordetella pertussis*, this is a classic **respiratory tract infection** transmitted via airborne droplets during coughing or sneezing. **High-Yield Clinical Pearls for NEET-PG:** * **Fecal-Oral Route "Must-Knows":** Hepatitis A and E, Poliomyelitis, Cholera, Typhoid, and Rotavirus. * **HSV-1 vs. HSV-2:** HSV-1 is typically "above the waist" (gingivostomatitis), while HSV-2 is "below the waist" (genital herpes). * **Incubation Periods:** Always remember the IP for Leprosy (3–5 years) and Pertussis (7–14 days) as they are frequently tested.
Question 1156: What is considered the heart of a controlled trial?
- A. Blinding
- B. Matching
- C. Randomization (Correct Answer)
- D. Stratification
Explanation: **Explanation:** **Randomization** is considered the "heart" or the hallmark of a Randomized Controlled Trial (RCT). It is the statistical process by which participants are allocated into study and control groups purely by chance. 1. **Why Randomization is Correct:** * **Elimination of Selection Bias:** It ensures that the investigator cannot influence which patient receives which treatment. * **Comparability:** It is the only method that balances both **known and unknown confounding factors** between the groups at the start of the study. This ensures that any observed difference in outcome is due to the intervention alone. 2. **Why Other Options are Incorrect:** * **Blinding:** While crucial for eliminating observer and participant bias (ascertainment bias), it is not the defining feature of a trial's structure. A trial can be "open" (unblinded) but still be a controlled trial. * **Matching:** This is primarily used in **Case-Control studies** to ensure cases and controls are similar. In RCTs, randomization achieves this more effectively without the logistical difficulty of matching. * **Stratification:** This is a technique used *during* randomization to ensure equal distribution of a specific known variable (e.g., age or gender) across groups, but it is a refinement of randomization, not its substitute. **High-Yield Pearls for NEET-PG:** * **Randomization vs. Random Sampling:** Randomization ensures *comparability* (internal validity), while random sampling ensures *representativeness* (external validity). * **The "Gold Standard":** The Double-blind RCT is the gold standard in clinical research. * **Intention-to-Treat (ITT) Analysis:** This is the preferred method for analyzing RCT data to maintain the benefits of randomization even if participants drop out.
Question 1157: Dengue fever is transmitted by which type of mosquito?
- A. Tiger mosquito (Correct Answer)
- B. Jackal mosquito
- C. Wolf mosquito
- D. Lion mosquito
Explanation: **Explanation:** The correct answer is **Tiger mosquito**, which is the common name for ***Aedes albopictus*** (and sometimes used interchangeably for ***Aedes aegypti***). These mosquitoes are characterized by distinct white and black stripes on their body and legs, resembling a tiger. * **Aedes aegypti** is the primary vector for Dengue fever, while **Aedes albopictus** serves as a potent secondary vector. Both are "day-biters" (peak activity at dawn and dusk) and breed in artificial collections of clean water (e.g., flower pots, discarded tires). * **Incorrect Options (B, C, D):** These terms (Jackal, Wolf, and Lion mosquito) are not standard entomological names for vectors of human disease. They are distractors designed to test the candidate's specific knowledge of the "Tiger" moniker. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Characteristics:** *Aedes* mosquitoes are "nervous feeders," biting multiple people to complete a single blood meal, which leads to rapid outbreaks. * **Extrinsic Incubation Period:** The virus requires 8–10 days inside the mosquito before it can be transmitted to another human. * **Transovarial Transmission:** The virus can pass from the female mosquito to her eggs, allowing the virus to persist in the environment even during dry seasons. * **Other Diseases:** *Aedes* mosquitoes also transmit **Chikungunya, Zika, and Yellow Fever.** * **Control:** The most effective control measure is "source reduction" (eliminating stagnant water) and the use of Abate (Temephos) as a larvicide.
Question 1158: What is the incubation period of Haemophilus influenzae?
- A. 3 days (Correct Answer)
- B. 2 weeks
- C. 3 weeks
- D. 4 weeks
Explanation: **Explanation:** The incubation period of *Haemophilus influenzae* (specifically type b, or Hib) is typically short, ranging from **2 to 4 days**. Therefore, **Option A (3 days)** is the most accurate choice. * **Why Option A is correct:** *H. influenzae* is a fast-growing bacterium that colonizes the nasopharynx. Once it breaches the mucosal barrier to cause invasive disease (like meningitis, epiglottitis, or pneumonia), the progression is rapid. Most clinical manifestations appear within 72 hours of exposure. * **Why Options B, C, and D are incorrect:** Incubation periods of 2 to 4 weeks are characteristic of slow-growing pathogens or those with complex life cycles. For example: * **2 weeks:** Common for *Salmonella typhi* (Enteric fever) or Pertussis. * **3 weeks:** Typical for Mumps or Rubella. * **4 weeks:** Often seen in Hepatitis A or certain parasitic infections. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Humans are the only known reservoir. * **Transmission:** Respiratory droplets or direct contact with secretions. * **Most Common Presentation:** Historically, Hib was the leading cause of **bacterial meningitis** in children aged 6 months to 5 years. * **Vaccination:** The Hib vaccine is a **conjugate vaccine** (capsular polysaccharide PRP conjugated to a protein carrier). In India, it is administered as part of the **Pentavalent vaccine** (DPT + HepB + Hib) at 6, 10, and 14 weeks under the Universal Immunization Programme (UIP). * **Drug of Choice:** Ceftriaxone (3rd generation cephalosporin) for invasive disease; Rifampicin is used for chemoprophylaxis of close contacts.
Question 1159: What is a migration study used to investigate?
- A. Sociodemographic reasons for population migration
- B. Prevalence of a disease in a population
- C. Environmental and genetic factors in a population's disease patterns (Correct Answer)
- D. Diseases with long incubation periods
Explanation: **Explanation:** **Migration studies** are a specialized type of observational study used in epidemiology to distinguish between the roles of **genetics (nature)** and **environment (nurture)** in the etiology of a disease. **Why Option C is correct:** When a population moves from one geographical area to another (e.g., Japanese people migrating to the USA), they carry their genetic makeup but change their environment and lifestyle. * If the migrants' disease rates remain similar to their country of origin, the cause is likely **genetic**. * If the disease rates shift to match the host country, the cause is likely **environmental/lifestyle-related**. For example, migration studies famously showed that Japanese migrants to the US developed higher rates of colon cancer (matching the US) and lower rates of stomach cancer (unlike Japan), proving environmental factors were dominant. **Why other options are incorrect:** * **Option A:** This is a sociological or demographic inquiry, not the primary epidemiological purpose of a migration study. * **Option B:** Prevalence is measured by Cross-sectional studies. * **Option C:** Diseases with long incubation periods are typically studied using Cohort studies or Case-control studies. **High-Yield Pearls for NEET-PG:** * Migration studies are a subset of **Ecological Studies**. * They are particularly useful for studying chronic non-communicable diseases (NCDs) like cancer, hypertension, and CHD. * **Twin Studies** are the other major method used to separate genetic from environmental factors; if monozygotic twins have higher concordance rates than dizygotic twins, a genetic basis is suggested.
Question 1160: Surveillance is necessary for all the following diseases recommended by WHO except?
- A. Relapsing fever
- B. Malaria
- C. Plague
- D. Tuberculosis (Correct Answer)
Explanation: **Explanation:** The concept of **Surveillance** in epidemiology involves the continuous, systematic collection, analysis, and interpretation of health data. According to WHO guidelines, diseases are categorized based on the type of surveillance required. **Why Tuberculosis is the correct answer:** While Tuberculosis (TB) is a major public health concern and is monitored globally, it is **not** included in the list of diseases specifically recommended for **International Surveillance** under the International Health Regulations (IHR) or the specific WHO "Surveillance of Diseases" list (which focuses on epidemic-prone or eradicable diseases). TB is managed through routine programmatic monitoring (e.g., the NTEP in India) rather than the rapid-response surveillance systems designed for the other listed diseases. **Analysis of Incorrect Options:** * **Relapsing Fever:** Along with Louse-borne Typhus, this is specifically listed by WHO as a disease under international surveillance. * **Malaria:** It is a disease under global surveillance due to its epidemic potential and the goal of global elimination/eradication in specific regions. * **Plague:** This is one of the three "Quarantinable Diseases" (along with Cholera and Yellow Fever) that must be notified to WHO immediately under International Health Regulations. **High-Yield NEET-PG Pearls:** 1. **Diseases under International Surveillance (WHO):** Louse-borne typhus, Relapsing fever, Malaria, Paralytic Polio, Influenza, and Viral hemorrhagic fevers (e.g., Ebola). 2. **Quarantinable Diseases:** Cholera, Plague, and Yellow Fever. 3. **Surveillance vs. Monitoring:** Surveillance is a continuous process (like a video film), whereas monitoring is an intermittent assessment (like a snapshot). 4. **Sentinel Surveillance:** Used to identify missing cases and supplement passive surveillance (often used for HIV/STIs).
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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