Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 431: Which of the following best describes the structure of ICD-10?

A. Revised every 5 years
B. Consists of 10 chapters
C. Arranged in 3 volumes (Correct Answer)
D. Was produced by UNICEF

Explanation: The **International Classification of Diseases (ICD)** is a standard diagnostic tool for epidemiology, health management, and clinical purposes, maintained by the **World Health Organization (WHO)**. ### **Explanation of the Correct Answer** **Option C is correct.** The ICD-10 is structured into **three distinct volumes**, each serving a specific purpose: * **Volume 1 (Tabular List):** Contains the main classification (alphanumeric codes) arranged by body systems and etiology. * **Volume 2 (Instruction Manual):** Provides guidelines, rules, and instructions for recording and coding. * **Volume 3 (Alphabetical Index):** An index to the diseases and nature of injury, used to locate codes found in Volume 1. ### **Analysis of Incorrect Options** * **Option A:** ICD is not revised every 5 years. Historically, revisions occurred roughly every **10 years**. However, ICD-10 was used for nearly 30 years before ICD-11 was officially adopted in 2019 (implemented in 2022). * **Option B:** ICD-10 consists of **21 chapters** (not 10). These chapters use an alphanumeric coding scheme (A00 to Z99). * **Option D:** The ICD is produced and published by the **WHO**, not UNICEF. UNICEF focuses on child health and development, whereas WHO is the directing authority for international health work. ### **High-Yield NEET-PG Pearls** * **ICD-10 Structure:** It uses a **4-character alphanumeric code** (e.g., A15.0). The first character is a letter. * **ICD-11 Update:** The latest version (ICD-11) is fully digital, contains **26 chapters**, and uses a 4-character code with a letter in the second position. * **Dual Coding:** ICD-10 uses the **"Dagger and Asterisk"** system to code both the underlying generalized disease (dagger †) and its localized manifestation (asterisk *). * **Standardization:** The primary goal of ICD is to allow systematic recording, analysis, and comparison of mortality and morbidity data across different countries.

Question 432: Primary and secondary cases are used to define which epidemiological measure?

A. Generation time
B. Serial interval (Correct Answer)
C. Secondary attack rate
D. None of the above

Explanation: ### Explanation **Correct Answer: B. Serial interval** The **Serial Interval** is defined as the time interval between the onset of clinical symptoms in the **primary case** (the infector) and the onset of clinical symptoms in the **secondary case** (the infectee). It is a crucial measure in infectious disease epidemiology used to estimate the speed of spread of an epidemic. Because it relies on observable clinical symptoms, it is easier to measure in field settings than biological parameters. **Why other options are incorrect:** * **A. Generation time:** This refers to the time interval between the **receipt of infection** and the **maximal communicability** of the host. It focuses on the biological process of the pathogen rather than the clinical onset in primary/secondary cases. * **C. Secondary Attack Rate (SAR):** This is a measure of **infectivity** and spread within a closed group (like a household). It is calculated as the number of exposed persons developing the disease within the incubation period following exposure to a primary case, divided by the total number of susceptible contacts. It is a proportion/rate, not a time interval. **High-Yield Pearls for NEET-PG:** * **Incubation Period:** Time from entry of pathogen to the first appearance of signs/symptoms. * **Latent Period:** Time from infection to the onset of infectiousness (often shorter than the incubation period). * **Communicable Period:** The time during which an infectious agent may be transferred directly or indirectly from an infected person to another person. * If the **Serial Interval is shorter than the Incubation Period**, it indicates significant pre-symptomatic transmission (e.g., COVID-19).

Question 433: Primordial prevention is done in which population group?

A. Population with risk factors
B. Population without risk factors (Correct Answer)
C. Whole population with low prevalence of disease
D. Population with the disease

Explanation: ### Explanation **Correct Answer: B. Population without risk factors** **1. Why Option B is Correct:** Primordial prevention is the prevention of the **emergence or development of risk factors** in population groups in which they have not yet appeared. It focuses on discouraging the adoption of harmful lifestyles (e.g., smoking, sedentary habits, unhealthy eating) through individual and mass education. Since the goal is to stop the risk factor from ever developing, it is targeted at a population **without risk factors**. **2. Why Other Options are Incorrect:** * **Option A (Population with risk factors):** This describes **Primary Prevention**. Here, the risk factor is already present (e.g., a smoker or a person with hypertension), and the goal is to prevent the onset of the disease through specific protection (vaccines) or health promotion. * **Option C (Whole population with low prevalence):** While primordial prevention can be applied to a whole population, the defining characteristic is the absence of risk factors, not the prevalence of the disease. * **Option D (Population with the disease):** This describes **Secondary Prevention** (early diagnosis and treatment to prevent progress) or **Tertiary Prevention** (disability limitation and rehabilitation). **3. High-Yield Clinical Pearls for NEET-PG:** * **Target Audience:** Primordial prevention is most effective in **children and adolescents**, as this is when lifelong habits are formed. * **Key Strategy:** It primarily utilizes **National Policies** and **Mass Education** (e.g., taxing tobacco, urban planning for parks). * **The "Prevention Hierarchy":** * **Primordial:** No Risk Factor present. * **Primary:** Risk Factor present; No Disease. * **Secondary:** Disease present (early stage); No Complications. * **Tertiary:** Disease present (late stage); Aim to reduce disability. * **Classic Example:** Changing a country's dietary patterns to prevent an epidemic of obesity or CAD before it starts.

Question 434: The age and sex structure of a population can be described by a?

A. Life table
B. Correlation coefficient
C. Population pyramid (Correct Answer)
D. Bar chart

Explanation: ### Explanation **Correct Answer: C. Population pyramid** A **Population Pyramid** (also known as an age-sex pyramid) is a graphical representation of the distribution of a population by age groups and sex. * **Structure:** It consists of two back-to-back bar diagrams. The Y-axis represents age groups (usually in 5-year intervals), and the X-axis represents the number or percentage of the population. * **Convention:** By standard convention, **males** are shown on the left and **females** on the right. * **Significance:** The shape of the pyramid reflects the demographic history (birth rates, death rates) and predicts future growth. For example, a broad base indicates high fertility, while a narrow top indicates mortality in older age groups. **Why other options are incorrect:** * **A. Life table:** This is a statistical tool used to calculate life expectancy and the probability of dying at specific ages. It does not visually represent the current age-sex structure of a whole population. * **B. Correlation coefficient (r):** This is a biostatistical measure that quantifies the strength and direction of a linear relationship between two quantitative variables (e.g., height and weight). * **C. Bar chart:** While a population pyramid uses bars, a standard bar chart is used for comparing discrete categories. A population pyramid is a specific, specialized dual-histogram format. **High-Yield Facts for NEET-PG:** * **India’s Pyramid:** Currently transitioning from a broad-based pyramid to one with "bulging" middle-age groups (Demographic Dividend). * **Expansive Pyramid:** Triangular shape (e.g., developing countries); high birth and death rates. * **Constrictive Pyramid:** Narrow base (e.g., developed countries like Japan); low birth rates. * **Stationary Pyramid:** Rectangular shape; zero population growth. * **Dependency Ratio:** Can be derived from the pyramid by comparing the "dependent" groups (<15 and >64 years) to the "working" group (15–64 years).

Question 435: The life cycle of the malaria parasite in the mosquito is described as?

A. Propagative
B. Cyclopropagative (Correct Answer)
C. Cyclodevelopmental
D. None of the above

Explanation: ### Explanation In epidemiology, the relationship between a pathogen and its vector is classified based on whether the pathogen undergoes changes in form (development) or increases in number (multiplication) within the vector. **1. Why "Cyclopropagative" is Correct:** The malaria parasite (*Plasmodium*) undergoes **Cyclopropagative** transmission within the female *Anopheles* mosquito. * **Cyclo-:** Refers to a change in form (developmental cycle). The parasite transforms from gametocytes into ookinetes, oocysts, and finally sporozoites. * **Propagative:** Refers to multiplication. A single oocyst ruptures to release thousands of sporozoites, significantly increasing the parasite count. Since both development and multiplication occur, it is termed cyclopropagative. **2. Analysis of Incorrect Options:** * **Propagative (Option A):** The organism multiplies in number but does not change its form or undergo a developmental cycle. *Example: Plague bacilli in the rat flea.* * **Cyclodevelopmental (Option B):** The organism undergoes developmental changes (morphological stages) but does not multiply in number. *Example: Filarial parasite (Wuchereria bancrofti) in the Culex mosquito or Guinea worm in Cyclops.* **3. NEET-PG High-Yield Pearls:** * **Biological Transmission:** This includes all three types (Propagative, Cyclopropagative, Cyclodevelopmental). It is characterized by an **extrinsic incubation period** (the time required for the parasite to complete its cycle in the vector before it becomes infective). * **Mechanical Transmission:** The vector simply carries the pathogen on its body parts (e.g., Housefly carrying Typhoid or Cholera) without any biological interaction. * **Malaria Vector:** Only the female *Anopheles* mosquito is the vector because it requires a blood meal for egg production; the male mosquito feeds on plant juices.

Question 436: In a study evaluating the health hazards of a drug versus a placebo, the following results were obtained: Placebo group: 15225 people, 1605 affected. Drug group: 15225 people, 1804 affected. Which of the following is true regarding the risk reduction?

A. Relative risk reduction (RRR) is 11%, Absolute risk reduction (ARR) is 11%
B. RRR 11%, ARR 1% (Correct Answer)
C. RRR 1%, ARR 11%
D. RRR 1%, ARR 1%

Explanation: ### **Explanation** This question tests the ability to differentiate between **Absolute Risk Reduction (ARR)** and **Relative Risk Reduction (RRR)**, which are fundamental concepts in clinical epidemiology and evidence-based medicine. #### **1. Step-by-Step Calculation** * **Incidence in Placebo Group ($I_p$):** $1605 / 15225 \approx 0.105$ (or **10.5%**) * **Incidence in Drug Group ($I_d$):** $1804 / 15225 \approx 0.118$ (or **11.8%**) *Note: In this specific study, the drug actually increases the risk. However, for the purpose of calculating "reduction" or "difference" in the context of such MCQ options:* * **Absolute Risk Difference (ARR/ARI):** $|I_d - I_p| = |11.8\% - 10.5\%| = \mathbf{1.3\%}$ (Rounded to **1%**). * **Relative Risk Difference (RRR/RRI):** $\frac{\text{Absolute Difference}}{\text{Incidence in Control Group}} = \frac{1.3\%}{11.8\%} \approx \mathbf{11\%}$. The correct answer is **Option B** because the absolute difference between the two groups is roughly 1%, while the proportional (relative) difference compared to the baseline is approximately 11%. #### **2. Why Other Options are Wrong** * **Option A:** Incorrectly assumes ARR is 11%. ARR is the simple subtraction of rates, which is 1%, not 11%. * **Option C:** Swaps the values. RRR is always a larger percentage than ARR when the baseline incidence is low. * **Option D:** Incorrectly calculates RRR. RRR measures the *proportion* of the risk removed, not just the absolute percentage points. #### **3. High-Yield Clinical Pearls for NEET-PG** * **ARR (Absolute Risk Reduction):** Tells you the actual number of percentage points the risk changed. It is the most clinically honest way to present data. * **RRR (Relative Risk Reduction):** Often used in pharmaceutical marketing because it tends to look more "impressive" than ARR. * **Number Needed to Treat (NNT):** Calculated as $1 / \text{ARR}$. It represents how many patients must be treated to prevent one additional bad outcome. * **Memory Aid:** **A**bsolute = **A**rithmetic difference (Subtraction). **R**elative = **R**atio (Division).

Question 437: Which of the following statements is NOT true about tetanus?

A. Tetanus protection is maintained for 5 years if previously immunized.
B. Herd immunity is present for tetanus. (Correct Answer)
C. Tetanus cannot be eradicated.
D. Elimination of tetanus is defined as less than 1 case per 1000 live births.

Explanation: **Explanation** **Why Option B is the Correct Answer (The False Statement):** Herd immunity occurs when a significant portion of a population becomes immune to an infectious disease, thereby providing indirect protection to those who are not immune by reducing the chain of transmission. **Tetanus does not exhibit herd immunity** because it is not a communicable disease. The infection is acquired through environmental exposure (soil, dust, or manure containing *Clostridium tetani* spores) rather than person-to-person spread. Therefore, an immunized individual protects only themselves, not the community. **Analysis of Other Options:** * **Option A:** According to the National Immunization Schedule, if a person has been previously immunized, the protective antibody levels are generally considered to last for at least 5 years. In injury management, a booster is often not required if the last dose was within 5 years. * **Option C:** Tetanus **cannot be eradicated** because the causative agent, *C. tetani*, is a ubiquitous environmental saprophyte. We can eliminate the disease (clinical cases), but we cannot eliminate the spores from the soil. * **Option D:** **Neonatal Tetanus Elimination** is defined by the WHO as an incidence of **less than 1 case per 1,000 live births** in every district of a country. India achieved this milestone in 2015. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Typically 3–21 days (Average: 10 days). Shorter incubation periods correlate with a poorer prognosis. * **First Sign:** Trismus (Lockjaw) is the most common presenting symptom. * **Maternal and Neonatal Tetanus (MNT) Elimination:** India was declared MNT-free on July 14, 2015. * **Vaccine Type:** Tetanus toxoid is an **adsorbed toxoid**; it must never be frozen.

Question 438: A total of 5000 patients with glaucoma are identified and surveyed regarding family history of glaucoma. What is this study design called?

A. Case series report (Correct Answer)
B. Case-control study
C. Clinical trial
D. Cohort study

Explanation: ### Explanation **1. Why Case Series Report is Correct:** A **Case Series** is a descriptive study design that describes a group of individuals with a common characteristic (in this case, 5,000 patients with glaucoma). The study simply observes and describes the distribution of a variable (family history) within this specific group. * **Key Identifier:** There is **no comparison group** (no control group of people without glaucoma). Since the researcher is only looking at "cases" to identify patterns or generate hypotheses, it is a case series. **2. Why the Other Options are Incorrect:** * **B. Case-control study:** This requires two groups: Cases (with glaucoma) and Controls (without glaucoma). The study would then compare the frequency of family history between these two groups to calculate an Odds Ratio. * **C. Clinical trial:** This is an experimental study where an intervention (like a new drug) is applied to one group and compared against a placebo or standard treatment. * **D. Cohort study:** This starts with a group of exposed and unexposed individuals (e.g., those with and without family history) and follows them forward in time to see who develops glaucoma. It measures incidence and Relative Risk. **3. NEET-PG High-Yield Pearls:** * **Descriptive vs. Analytical:** Case reports and case series are *descriptive* (generate hypotheses). Case-control and cohort studies are *analytical* (test hypotheses). * **The "No Control" Rule:** If a question describes a large number of patients with a disease but mentions no comparison group, the answer is almost always a **Case Series**. * **Hierarchy of Evidence:** Case series are low on the evidence pyramid because they cannot prove a causal association due to the lack of a control group.

Question 439: Confounding factors can be eliminated by all except:

A. Matching
B. Randomization
C. Ethical consideration (Correct Answer)
D. Stratification

Explanation: ### Explanation Confounding occurs when the association between an exposure and an outcome is distorted by a third variable (the confounder) that is associated with both. To ensure the internal validity of a study, confounding must be managed either at the **design stage** or the **analysis stage**. **Why "Ethical Consideration" is the Correct Answer:** Ethical considerations (such as informed consent or beneficence) are fundamental requirements for conducting research involving human subjects. However, they are **not a statistical or methodological tool** for controlling bias or confounding. Adhering to ethics ensures the safety and rights of participants but does not influence the distribution of variables or the accuracy of the association being studied. **Why the other options are incorrect:** * **Randomization (Design Stage):** Often called the "heart of a clinical trial," it is the most effective method because it balances both **known and unknown** confounders between the study and control groups. * **Matching (Design Stage):** This involves selecting controls who possess the same confounding characteristics (e.g., age, sex) as the cases. It neutralizes the effect of those specific known confounders. * **Stratification (Analysis Stage):** This involves analyzing the data in sub-groups (strata) based on the confounding variable (e.g., analyzing results separately for smokers and non-smokers) to see if the association persists. --- ### High-Yield Pearls for NEET-PG * **Methods at Design Stage:** Randomization, Matching, and Restriction (limiting the study to a specific group, e.g., only males). * **Methods at Analysis Stage:** Stratification and Multivariate Analysis (e.g., Logistic Regression). * **Gold Standard:** Randomization is the only method that controls for **unknown** confounders. * **Definition of a Confounder:** It must be associated with the exposure, be a risk factor for the disease, and **not** be an intermediate step in the causal pathway.

Question 440: Screening is useful for which of the following conditions?

A. A disease which is an important health problem
B. A disease which can be diagnosed at a latent stage
C. A disease where early diagnosis and treatment favorably alters the natural history in a significant proportion of cases
D. All of the above (Correct Answer)

Explanation: ### Explanation Screening is the process of identifying apparently healthy individuals who may have a disease, but do not yet have symptoms. For a screening program to be considered ethical and effective, it must fulfill the **Wilson and Jungner criteria**. **Why "All of the Above" is Correct:** The options provided represent the fundamental prerequisites for screening: * **Option A:** The disease must be an **important health problem** (high prevalence or high mortality/morbidity) to justify the cost and resources of a mass program. * **Option B:** There must be a recognizable **latent or early asymptomatic stage** (the "DPCP" or Lead Time) during which the disease can be detected. * **Option C:** This is the most critical ethical criterion. Screening is only useful if **early intervention** leads to a better prognosis than treatment at the symptomatic stage. If the outcome remains the same regardless of when treatment starts, screening is futile. **Analysis of Options:** Since all three criteria (importance of the disease, detectability in the latent phase, and benefit of early treatment) are essential components of a successful screening program, "All of the above" is the most comprehensive answer. **High-Yield NEET-PG Pearls:** * **Lead Time:** The period between early detection by screening and the time the disease would have been diagnosed clinically. * **DPCP (Detectable Pre-Symptomatic Check-up Period):** The interval between the first possible point of detection and the onset of symptoms. * **Iceberg Phenomenon:** Screening is primarily aimed at the "submerged portion" of the iceberg (latent, undiagnosed cases). * **Yield:** The amount of previously unknown disease detected in the population. * **Gold Standard:** The diagnostic test against which the screening test is compared (e.g., Biopsy for Cancer).

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

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