Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 581: Potential Support Ratio (PSR) is defined as:

A. Number of persons aged 15-65 per children below 15 years
B. Number of persons aged 15-65 per one older person aged >= 65 years (Correct Answer)
C. Number of persons aged 15-65 per one older person aged > 65 and younger person < 15 years
D. Number of persons aged 15-65 per one older person aged > 60 and younger person < 15 years

Explanation: **Explanation:** **Potential Support Ratio (Ratio of the Working-Age Population to the Elderly)** The Potential Support Ratio (PSR) is a demographic indicator used to measure the "burden" on the working-age population to support the elderly. It is defined as the number of persons aged **15 to 64 years** per one person aged **65 years or older**. * **Why Option B is Correct:** In epidemiology and demographics, the "working-age" is traditionally defined as 15–64 years, while the "elderly" are those ≥65 years. The PSR specifically focuses on the relationship between these two groups to estimate how many potential workers are available to support each retiree. As life expectancy increases and fertility rates drop, the PSR decreases, indicating an aging population. **Analysis of Incorrect Options:** * **Option A:** This describes a variation of the Child Dependency Ratio, not the PSR. * **Options C & D:** These options describe the **Total Dependency Ratio**, which accounts for both children (<15) and the elderly (>60 or 65) relative to the working-age population. PSR is specific only to the elderly. **High-Yield Facts for NEET-PG:** * **Dependency Ratio Formula:** $\frac{(\text{Persons } 0-14) + (\text{Persons } 65+)}{\text{Persons } 15-64} \times 100$. * **Old-Age Dependency Ratio:** Specifically looks at the elderly population relative to the working population. * **Demographic Dividend:** Occurs when the PSR is high (a large working-age population relative to dependents), potentially accelerating economic growth. * **Trend:** Globally, PSR is declining. A lower PSR suggests a higher social and economic pressure on the healthcare system and social security.

Question 582: Ability of a screening test to diagnose true positives refers to:

A. Relative risk
B. Sensitivity (Correct Answer)
C. Specificity
D. Attributable risk

Explanation: ### Explanation **Correct Option: B. Sensitivity** Sensitivity is the ability of a screening test to correctly identify those who **actually have the disease** (True Positives). Mathematically, it is the proportion of people with the disease who test positive: * **Formula:** [True Positives (TP) / (True Positives + False Negatives (FN))] × 100. A highly sensitive test is essential for screening because it ensures that very few cases are missed (low false-negative rate). **Why Incorrect Options are Wrong:** * **C. Specificity:** This refers to the ability of a test to correctly identify those **without the disease** (True Negatives). It is the proportion of healthy individuals who test negative. * **A. Relative Risk (RR):** This is a measure of **association** used in cohort studies. It compares the incidence of disease in an exposed group to the incidence in an unexposed group. * **D. Attributable Risk (AR):** This indicates the amount of disease incidence that can be attributed to a specific exposure. it is calculated as [Incidence in exposed – Incidence in unexposed]. **High-Yield Clinical Pearls for NEET-PG:** * **SNOUT:** A highly **S**ensitive test, when **N**egative, rules **OUT** the disease (useful for screening). * **SPIN:** A highly **S**pecific test, when **P**ositive, rules **IN** the disease (useful for confirmation). * **Screening vs. Diagnostic:** Screening tests prioritize **Sensitivity** (to catch all cases), while diagnostic tests prioritize **Specificity** (to confirm the diagnosis). * **Predictive Values:** Unlike sensitivity/specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) are highly dependent on the **prevalence** of the disease in the population.

Question 583: Which of the following is true about a single exposure, common vector outbreak?

A. Explosive onset (Correct Answer)
B. Secondary waves occur
C. Cases occur with varying incubation periods
D. Depends on herd immunity

Explanation: ### Explanation In epidemiology, outbreaks are classified based on the nature of exposure. A **single exposure, common source outbreak** (also known as a point-source epidemic) occurs when a group of people is exposed to the same source of infection simultaneously or over a very short period. **1. Why "Explosive Onset" is Correct:** Because all susceptible individuals are exposed to the noxious agent at the same time, the number of cases rises very sharply. This results in a characteristic **"explosive"** increase in cases, forming a steep upward curve. All cases typically occur within one incubation period of the disease. **2. Analysis of Incorrect Options:** * **B. Secondary waves occur:** Secondary waves are characteristic of **Propagated (Person-to-Person) epidemics**, where the infection spreads from host to host. In a single-exposure common source outbreak, the source is removed or the exposure is brief, so there is no secondary spread. * **C. Cases occur with varying incubation periods:** While there is slight variation due to individual host immunity, the hallmark of this outbreak is that cases are clustered within **one incubation period**. Wide variations are seen in "Continuous or Repeated Exposure" outbreaks. * **D. Depends on herd immunity:** Herd immunity primarily influences the spread of **communicable diseases** in a population over time (propagated spread). A point-source outbreak (like food poisoning at a wedding) depends more on the dose of the pathogen and individual susceptibility rather than the population's collective immunity. **High-Yield NEET-PG Pearls:** * **Epidemic Curve:** In a point-source epidemic, the curve has a **sharp rise and a more gradual decline**. * **Median Incubation Period:** Can be calculated from the epidemic curve by identifying the time when 50% of cases have occurred. * **Classic Example:** A Bhopal Gas Tragedy (non-infectious) or a contaminated food item at a single party (infectious). * **Key Distinction:** If the exposure continues over time (e.g., a contaminated well), it is a **Continuous Common Source** outbreak, and the curve will have a plateau rather than a sharp peak.

Question 584: At what point is the zero dose of the polio vaccine administered?

A. Before giving DPT
B. At birth (Correct Answer)
C. When the child has diarrhea
D. When the child has polio

Explanation: **Explanation:** The **Zero Dose** of Oral Polio Vaccine (OPV) refers to the dose administered **at birth** (or as soon as possible within the first 15 days). The primary objective of this dose is to induce local mucosal immunity in the gut before the infant can be exposed to enteric pathogens. It also helps overcome the interference of maternal antibodies that might affect later doses. **Analysis of Options:** * **Option B (Correct):** Under the Universal Immunization Programme (UIP), OPV-0 is given at birth. It is called "zero" because it does not count toward the primary three-dose series (given at 6, 10, and 14 weeks). * **Option A:** DPT (now part of the Pentavalent vaccine) is started at 6 weeks. Waiting until this point would miss the window for early mucosal priming. * **Option C:** Diarrhea is not a contraindication for OPV. In fact, if a child has diarrhea during a routine dose, that dose is administered but not counted; an extra dose is given after recovery. However, this does not define the "zero dose." * **Option D:** If a child already has polio (paralysis), the vaccine will not cure the condition, though they should still be immunized to prevent infection from other strains (Type 1 or 3). **High-Yield NEET-PG Pearls:** * **Type of Vaccine:** OPV (Sabin) is a Live Attenuated vaccine; IPV (Salk) is Killed. * **Storage:** OPV is the most heat-sensitive vaccine; stored at **-20°C**. * **VVM (Vaccine Vial Monitor):** Used to monitor heat exposure. The vaccine is usable as long as the inner square is lighter than the outer circle. * **Current Schedule:** India currently uses **bOPV** (Types 1 & 3) and has introduced **Fractional IPV (fIPV)** at 6 and 14 weeks (intradermal).

Question 585: True regarding case-control study are all of the following except?

A. Possibility of bias
B. Odds ratio can be derived
C. Relatively inexpensive
D. Attributable risk can be known (Correct Answer)

Explanation: **Explanation:** In epidemiology, the choice of study design dictates which measures of association can be calculated. The correct answer is **D** because **Attributable Risk (AR)** and **Relative Risk (RR)** cannot be directly calculated from a case-control study; they require **Incidence** data, which is only provided by Cohort studies. **1. Why Option D is the correct answer (The "Except"):** Case-control studies are retrospective; they start with the outcome (disease) and look backward for exposure. Since we do not follow a population over time to see how many new cases develop, we cannot calculate the *Incidence*. Attributable Risk (Incidence in exposed - Incidence in non-exposed) and Relative Risk both require incidence rates as their denominator. **2. Analysis of Incorrect Options:** * **A. Possibility of bias:** True. Case-control studies are highly prone to **Recall Bias** (cases remember exposures better than controls) and **Selection Bias**. * **B. Odds Ratio (OR) can be derived:** True. The Odds Ratio is the characteristic measure of association for case-control studies. It serves as an estimate of Relative Risk when the disease is rare. * **C. Relatively inexpensive:** True. Because they do not require long-term follow-up and usually involve smaller sample sizes, they are faster and cheaper than cohort studies. **High-Yield NEET-PG Pearls:** * **Case-Control Study:** Best for **rare diseases** or diseases with long latency periods. * **Cohort Study:** Best for **rare exposures**; allows calculation of Incidence, RR, and AR. * **Formula for OR:** $(a/c) / (b/d)$ or $ad/bc$. * **Nesting:** A "Nested Case-Control" study is a case-control study conducted within a cohort study, reducing selection and information bias.

Question 586: What method is used for the disinfection of sputum?

A. Boiling
B. Autoclaving (Correct Answer)
C. Sunlight
D. Burning

Explanation: **Explanation:** The disinfection of sputum is a critical practice in infection control, particularly for preventing the transmission of *Mycobacterium tuberculosis*. **Why Autoclaving is Correct:** Autoclaving (moist heat under pressure) is considered the **gold standard** and the most reliable method for disinfecting sputum. It ensures the complete destruction of all forms of microbial life, including highly resistant mycobacteria and bacterial spores. In a hospital or laboratory setting, sputum containers are typically autoclaved at 121°C (15 lbs pressure) for 20–30 minutes before final disposal, ensuring absolute sterilization. **Analysis of Incorrect Options:** * **Boiling:** While boiling kills most vegetative pathogens, it is not considered a method of sterilization as it may fail to kill resistant spores. It is also less practical and carries a higher risk of aerosolization or spills compared to contained autoclaving. * **Sunlight:** Although UV rays in sunlight have some germicidal properties against *M. tuberculosis*, this method is slow, unreliable, and dependent on weather conditions. It is insufficient for clinical disinfection. * **Burning (Incineration):** While incineration is the final method for **disposal** of biomedical waste (Category Yellow), the question asks for the method of **disinfection**. In many protocols, sputum is first disinfected/pre-treated (via autoclaving or 5% cresol) before being sent for final disposal. **High-Yield Clinical Pearls for NEET-PG:** * **Chemical Disinfection:** If autoclaving is unavailable, **5% Cresol** (for 24 hours) or **1% Sodium Hypochlorite** are the preferred chemical disinfectants for sputum. * **Biomedical Waste Management:** Sputum cups and infected secretions fall under **Yellow Category** waste. * **Pre-treatment:** According to BMW guidelines, laboratory waste and specimens like sputum should be pre-treated (disinfected) on-site by autoclaving before being sent for final disposal.

Question 587: Increased motivation by a teacher has been found to increase the marks of students in examinations. This bias is called:

A. Berksonian bias
B. Pygmalion bias (Correct Answer)
C. Hawthorne bias
D. Motivational bias

Explanation: ### Explanation The correct answer is **Pygmalion bias** (also known as the **Rosenthal effect**). **1. Why Pygmalion Bias is Correct:** Pygmalion bias occurs when a researcher’s or teacher’s high expectations of a subject lead to improved performance in that subject. In this scenario, the teacher’s increased motivation and belief in the students act as a self-fulfilling prophecy, subconsciously influencing the students to perform better. In clinical research, this is a type of **investigator bias** where the doctor’s expectations can inadvertently influence the patient’s outcome or the recording of data. **2. Analysis of Incorrect Options:** * **Berksonian Bias (Admission Rate Bias):** This is a type of selection bias that occurs when the sample is taken from a hospital population rather than the general community. It arises because hospitalized individuals have different exposure/disease patterns than the general public. * **Hawthorne Bias:** This occurs when study participants change their behavior simply because they **know they are being observed**, rather than due to any specific intervention or expectation. * **Motivational Bias:** While it sounds plausible, this is not a standard epidemiological term for this phenomenon. It generally refers to errors in judgment caused by the desire to achieve a certain outcome. **3. Clinical Pearls for NEET-PG:** * **Self-fulfilling Prophecy:** Pygmalion effect (Positive expectations → Positive results). * **Golem Effect:** The opposite of Pygmalion; low expectations lead to a decrease in performance. * **Prevention:** The best way to eliminate Pygmalion/Investigator bias in clinical trials is through **Double Blinding**, where neither the investigator nor the participant knows who is receiving the intervention. * **Recall Bias:** Common in Case-Control studies; patients with the disease remember past exposures more clearly than healthy controls.

Question 588: What are the features of the Revised National Tuberculosis Control Programme (RNTCP)/DOTS Expansion?

A. Active case finding is not done.
B. Included in National Rural Health Mission (NRHM) in 2005. (Correct Answer)
C. Teachers act as DOTS agents.
D. Microscopy centers are established per 1 lac population.

Explanation: The Revised National Tuberculosis Control Programme (RNTCP) is a cornerstone of public health in India. Understanding its structural integration and operational guidelines is crucial for NEET-PG. ### **Explanation of the Correct Answer** **Option B** is correct because RNTCP was formally integrated into the **National Rural Health Mission (NRHM)** in **2005**. This integration was a strategic move to decentralize TB services, improve health system synergy, and utilize the NRHM’s vast infrastructure (like ASHAs) to enhance reach and sustainability. ### **Analysis of Incorrect Options** * **Option A:** RNTCP/NTEP primarily relies on **Passive Case Finding** (patients reporting to clinics). However, the statement "Active case finding is not done" is technically incorrect in the current context, as **Active Case Finding (ACF)** was introduced in 2017 to target vulnerable populations. * **Option C:** While teachers *can* be DOTS providers, they are not the primary agents. The program prioritizes health workers, ASHAs, or community volunteers who are accessible to the patient. * **Option D:** Under RNTCP guidelines, **Designated Microscopy Centers (DMCs)** are established for every **1 lakh (100,000) population** in general areas, and every **50,000 population** in hilly, tribal, or difficult terrains. ### **High-Yield Clinical Pearls for NEET-PG** * **Evolution:** RNTCP was launched in 1993 and renamed the **National Tuberculosis Elimination Program (NTEP)** in 2020. * **Goal:** India aims to eliminate TB by **2025**, five years ahead of the global SDG target (2030). * **Diagnostic Algorithm:** The current protocol emphasizes **CBNAAT/NAAT** as the initial diagnostic test for all presumptive TB cases, moving away from sputum microscopy as the sole primary tool. * **Nikshay Poshan Yojana:** Provides ₹500/month nutritional support to all TB patients.

Question 589: Which of the following diseases are under international surveillance?

A. Poliomyelitis
B. Rabies
C. Malaria
D. All of the above (Correct Answer)

Explanation: **Explanation:** The concept of **International Surveillance** refers to the systematic, ongoing collection and analysis of health data by the World Health Organization (WHO) to monitor diseases that pose a significant threat to global public health. Under the current WHO framework, international surveillance is categorized into two main groups: 1. **Diseases under the International Health Regulations (IHR 2005):** These are diseases that must be reported to the WHO because they may constitute a Public Health Emergency of International Concern (PHEIC). This includes **Poliomyelitis** (wild-type), Ebola, and Human Influenza caused by a new subtype. 2. **Diseases under Global Surveillance:** The WHO also maintains active surveillance for diseases that have significant international implications due to their morbidity, mortality, or potential for cross-border spread. This list includes **Malaria** and **Rabies**, along with others like Salmonellosis, Influenza, and SARS. **Analysis of Options:** * **Poliomyelitis (A):** It is a high-priority disease under IHR due to the global eradication goal. Any case of wild poliovirus is considered a global emergency. * **Rabies (B):** While not a "notifiable" disease under IHR in the same way as Polio, it is under constant international surveillance due to its 100% fatality rate and zoonotic importance. * **Malaria (C):** It is monitored globally to track drug resistance, vector distribution, and progress toward elimination in various regions. Since all three diseases are subject to international monitoring and reporting protocols, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **IHR (2005):** Currently, only three diseases are "automatically" notifiable to WHO: **Smallpox, Poliomyelitis (wild-type), and Human Influenza (new subtype).** * **Surveillance vs. Monitoring:** Surveillance is continuous and action-oriented; monitoring is the intermittent performance and analysis of routine measurements. * **Sentinel Surveillance:** Used to identify missing cases and supplement passive surveillance (often tested in NEET-PG).

Question 590: What best describes demographic transition?

A. A state where the birth rate and death rate are both low and similar. (Correct Answer)
B. A state where there is a large difference between the crude birth rate and crude death rate.
C. A significant imbalance in the sex ratio within the population.
D. A population characterized by a high proportion of individuals at the extreme age ranges.

Explanation: **Explanation** **Demographic Transition** refers to the historical shift of a population from high birth and death rates to low birth and death rates as a country develops from a pre-industrial to an industrialized economic system. **Why Option A is correct:** The ultimate goal and final stage (Stage 4/5) of demographic transition is a state of **low stationary equilibrium**. In this stage, both birth rates and death rates have declined significantly and are approximately equal. This results in zero or very low population growth, reflecting advanced socio-economic development, effective family planning, and high-quality healthcare. **Why the other options are incorrect:** * **Option B:** A large difference between birth and death rates characterizes the **"Population Explosion"** phase (Stage 2 and early Stage 3). Here, death rates fall rapidly due to medical advances, but birth rates remain high, leading to rapid natural increase. * **Option C:** Imbalance in the sex ratio is a demographic indicator but does not define the transition process itself. * **Option D:** While a "low birth/low death" population eventually leads to an **aging population** (more elderly), the transition itself describes the shift in vital rates (birth/death), not just the age distribution. **High-Yield NEET-PG Pearls:** * **Stage 1 (High Stationary):** High birth rate, high death rate (e.g., India in the 1920s). * **Stage 2 (Early Expanding):** Death rate begins to decline; birth rate remains high. * **Stage 3 (Late Expanding):** Birth rate begins to decline; death rate continues to fall. **India is currently in late Stage 3.** * **Stage 4 (Low Stationary):** Low birth rate, low death rate. * **Stage 5 (Declining):** Birth rate falls below death rate (Negative growth; e.g., Germany, Japan).

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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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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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