Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1701: What does the secondary attack rate measure?

A. The ability of a disease to spread from one person to another
B. The proportion of susceptible people who become infected after exposure to a primary case (Correct Answer)
C. The ability of a disease to cause death
D. The rate at which a disease progresses in severity

Explanation: ***The proportion of susceptible people who become infected after exposure to a primary case*** - This is the **correct definition** of the **secondary attack rate (SAR)** - SAR = (Number of new cases among contacts of primary cases) / (Total number of susceptible contacts at risk) - It is typically measured within one incubation period after exposure - Commonly used to assess transmission in **households or closed populations** (schools, institutions, etc.) - Important measure of **communicability** of infectious diseases in real-world settings *The ability of a disease to spread from one person to another* - This broadly describes **transmissibility** or **infectivity** but is too general - The **basic reproductive number (R₀)** is the specific measure of disease spread in a fully susceptible population - SAR is more specific, measuring spread among actual contacts *The ability of a disease to cause death* - This describes **case fatality rate (CFR)** or **virulence** - CFR = (Number of deaths from disease) / (Total number of cases) × 100 - Completely different concept from secondary attack rate *The rate at which a disease progresses in severity* - This describes **disease progression** or **natural history** of disease - Not related to the secondary attack rate concept - SAR measures **spread between people**, not progression within an individual

Question 1702: Secondary attack rate of mumps?

A. 95%
B. < 50%
C. 85%
D. 75% (Correct Answer)

Explanation: ***75%*** - The **secondary attack rate** for mumps is approximately **75%**, indicating its high transmissibility among susceptible household contacts. - This high rate underscores the importance of vaccination to prevent spread in close-contact settings. *85%* - While mumps is highly contagious, an 85% secondary attack rate is generally considered too high and not reflective of typical epidemiological data. - This percentage is more commonly associated with diseases like measles, which has an even higher transmissibility. *95%* - A 95% secondary attack rate is characteristic of highly contagious diseases like **measles**, which transmit very efficiently even in short, casual contacts. - Mumps, while highly infectious, does not typically reach this level of secondary attack rate. *< 50%* - A secondary attack rate of less than 50% would suggest lower transmissibility than what is observed for mumps. - Diseases with lower secondary attack rates are generally less prone to rapid outbreaks among close contacts.

Question 1703: What is the primary difference between descriptive and analytic studies in epidemiology?

A. Analytic studies test hypotheses about relationships between health outcomes and exposures.
B. Descriptive studies are always retrospective while analytic studies are prospective.
C. Descriptive studies describe the distribution of health outcomes in a population.
D. Descriptive studies do not test hypotheses but generate them. (Correct Answer)

Explanation: ***Descriptive studies do not test hypotheses but generate them*** - **Descriptive epidemiology** focuses on identifying patterns, trends, and frequencies of health events, often summarized by person, place, and time. - While they do not formally test hypotheses, they are crucial for **generating new hypotheses** that can then be investigated by analytic studies. - This is the **primary and fundamental difference** between descriptive and analytic approaches in epidemiology. *Analytic studies test hypotheses about relationships between health outcomes and exposures* - This statement accurately describes analytic studies, which formally test hypotheses. - However, it only describes one side (analytic) without contrasting it with the key feature of descriptive studies. - It doesn't capture the **primary difference** by showing both sides of the distinction. *Descriptive studies are always retrospective while analytic studies are prospective* - This is **incorrect** - both descriptive and analytic studies can be either retrospective or prospective. - For example, **cohort studies** (analytic) can be retrospective, and **cross-sectional surveys** (descriptive) can be prospective. - Study design timing is independent of whether a study is descriptive or analytic. *Descriptive studies describe the distribution of health outcomes in a population* - This is a correct characteristic of descriptive studies, as they quantify health events by **person, place, and time**. - While true, it only describes what descriptive studies do, without addressing the fundamental difference of **hypothesis generation vs. hypothesis testing**.

Question 1704: Which of the following statements about natural experiments is false?

A. Researcher has no control over the allocation of subjects
B. All are correct
C. They utilize naturally occurring events or policy changes to approximate experimental conditions
D. Includes Randomized controlled trials [RCTs] as an example of natural experiments. (Correct Answer)

Explanation: ***Includes Randomized controlled trials [RCTs] as an example of natural experiments*** - This statement is **false** because **Randomized Controlled Trials (RCTs)** are a form of **experimental study design** where researchers actively intervene and randomly assign participants to treatment or control groups. - In contrast, **natural experiments** capitalize on naturally occurring events or policies that create exposure groups without direct researcher intervention. - RCTs are the gold standard for experimental studies, while natural experiments are a type of **observational study** that mimics experimental conditions. *Researcher has no control over the allocation of subjects* - This statement is **true** and accurately describes a key characteristic of **natural experiments**. - The exposure or intervention is determined by nature, policy changes, or external circumstances, not by the researcher. - The lack of researcher control over allocation is what fundamentally differentiates natural experiments from true experimental designs like RCTs. *They utilize naturally occurring events or policy changes to approximate experimental conditions* - This statement is **true** and describes the fundamental principle of natural experiments. - Examples include studying health effects of smoking bans, natural disasters, or policy implementations that create "treatment" and "control" groups naturally. - These studies leverage real-world variations to draw causal inferences. *All are correct* - This statement is **false** because the option "Includes RCTs as an example of natural experiments" is definitively incorrect.

Question 1705: Which of the following statements is true regarding the iceberg of disease?

A. The tip of the iceberg represents the clinical cases. (Correct Answer)
B. Screening is primarily done for the tip of the iceberg.
C. Hypertension is a classical example of the iceberg of disease.
D. The clinician is primarily concerned with the hidden portion of the iceberg.

Explanation: ***The tip of the iceberg represents the clinical cases.*** - The **"iceberg phenomenon"** in epidemiology illustrates that only a small proportion of a disease's true burden (the "tip") is outwardly visible or clinically apparent. - These visible cases are the ones that present to healthcare facilities or are **diagnosed clinically**. - This is a **fundamental definition** of the iceberg concept and is universally true. *Screening is primarily done for the tip of the iceberg.* - **Screening programs** are primarily designed to detect the **"submerged portion"** (unapparent, preclinical, or undiagnosed cases) of the iceberg, not the already clinically evident "tip." - The goal of screening is **early detection** to prevent progression or reduce morbidity and mortality. - This statement is **incorrect** as it reverses the actual purpose of screening. *Hypertension is a classical example of the iceberg of disease.* - While hypertension is indeed **a good example** of the iceberg phenomenon with significant undiagnosed burden, the statement uses definite article "**a classical example**" rather than "**the only example**." - The iceberg concept applies to **many diseases** including both communicable (TB, polio, hepatitis) and non-communicable diseases (hypertension, diabetes, cancers). - This is **a valid example but not a defining characteristic** of the iceberg phenomenon itself, making Option A a more fundamentally correct statement about the concept. *The clinician is primarily concerned with the hidden portion of the iceberg.* - A **clinician's primary role** is to diagnose and treat patients who present with **clinical symptoms** (the "tip of the iceberg"). - **Public health professionals** and epidemiologists are more concerned with understanding and addressing the "hidden portion" through surveillance, screening, and prevention strategies. - This statement **reverses the actual roles** and is therefore incorrect.

Question 1706: In the context of epidemiology, standardization is most important for which of the following distributions?

A. Sex distribution
B. Age distribution (Correct Answer)
C. Disease distribution
D. None of the options

Explanation: ***Age distribution*** - **Standardization** (e.g., age adjustment) is crucial when comparing health outcomes or disease rates between populations with different **age structures**. - This method removes the confounding effect of age, allowing for a more accurate comparison of underlying risk factors or disease incidence. *Sex distribution* - While sex can influence disease prevalence, its distribution is generally less variable and confounding than age when comparing populations, making standardization for sex less universally critical than for age. - Differences in sex distribution can still be accounted for, but often through direct stratification rather than complex standardization methods. *Disease distribution* - **Disease distribution** itself is what we often aim to measure and compare, rather than a characteristic necessitating standardization to understand other variables. - Standardization techniques are applied to demographic features (like age or sex) to understand their impact on disease distribution, not to the disease distribution itself. *None of the options* - This option is incorrect because **age distribution** is a primary factor where standardization is essential in epidemiology to ensure valid comparisons. - Ignoring age differences when comparing populations can lead to misleading conclusions about disease risk or health statuses.

Question 1707: Major reservoir of KFD?

A. Human
B. Squirrels (Correct Answer)
C. Cattle
D. Monkey

Explanation: ***Squirrels*** - **Squirrels** are considered a major reservoir for the Kyasanur Forest Disease (KFD) virus because they can carry the virus without showing severe symptoms themselves, allowing for viral persistence in nature. - The virus can be transmitted from infected squirrels to ticks, which then can spread the infection to other animals or humans. *Human* - Humans are considered **incidental hosts** for KFD, meaning they can become infected but do not typically play a significant role in maintaining the virus in nature. - While humans can experience severe disease, they do not serve as a reservoir for further transmission to other vectors or hosts. *Cattle* - **Cattle** are not typically considered a reservoir for the Kyasanur Forest Disease virus. - They can be exposed to KFD but are not known to sustain the viral cycle or transmit it effectively to ticks or other animals. *Monkey* - While KFD is often associated with **monkey deaths** (especially black-faced langurs and bonnet macaques), these animals are considered **amplifying hosts** rather than primary reservoirs. - Monkeys experience severe disease and high mortality, making them good indicators of viral activity but not long-term carriers for sustained transmission.

Question 1708: What is the expected effect on incidence [I] and prevalence [P] when an effective treatment for a disease is introduced in a community?

A. No change in P & I
B. Both P & I will decrease
C. P will decrease & I will increase
D. P will decrease & I will remain the same (Correct Answer)

Explanation: ***P will decrease & I will remain the same*** - An effective treatment reduces the **duration of disease** by curing existing cases faster, which directly decreases **prevalence** (P = Incidence × Duration) - **Incidence** measures the rate of *new cases* occurring, which is unaffected by treatment of existing cases, so **incidence remains unchanged** - This is the fundamental epidemiological principle for treatment interventions *No change in P & I* - Incorrect because effective treatment shortens disease duration, which must reduce the number of existing cases at any given time - **Prevalence** will definitely decrease when cases recover faster *Both P & I will decrease* - While treatment correctly decreases **prevalence** by shortening disease duration, it does not prevent *new infections* from occurring - **Incidence** (new case rate) remains unchanged unless there's a preventive intervention like vaccination or behavioral change *P will decrease & I will increase* - Correctly identifies that **prevalence** decreases with effective treatment - However, there's no mechanism by which treatment would increase **incidence** of new cases - Treatment affects existing patients, not the rate of new infections

Question 1709: Which of the following statements is not true regarding the International Classification of Diseases?

A. It is revised once in 10 years
B. It was devised by UNICEF (Correct Answer)
C. It is accepted for National and International use
D. The 10th revision consists of 22 major chapters

Explanation: ***It was devised by UNICEF*** **(CORRECT - This statement is FALSE)** - The **International Classification of Diseases (ICD)** was developed and maintained by the **World Health Organization (WHO)**, not UNICEF. - **UNICEF** focuses on children's welfare and health, while **WHO** is the primary international health agency responsible for global health standards. - Since the question asks for the statement that is **NOT TRUE**, this is the correct answer. *It is revised once in 10 years* **(Incorrect - This statement is TRUE)** - The **ICD** is indeed typically revised approximately every **10 years** to incorporate new medical knowledge, diseases, and public health needs. - This regular revision cycle ensures the classification remains relevant and up-to-date with medical advancements and epidemiological trends. *It is accepted for National and International use* **(Incorrect - This statement is TRUE)** - The **ICD** is widely accepted and used globally by countries for **mortality and morbidity statistics**, health management, and reimbursement systems. - Its standardization allows for consistent **data collection** and comparison of health information across different regions and countries. *The 10th revision consists of 22 major chapters* **(Incorrect - This statement is TRUE)** - **ICD-10** (the 10th revision) is structured into **22 chapters**, each covering a specific category of diseases and health problems. - These chapters organize diagnoses logically, facilitating **data coding** and analysis in healthcare.

Question 1710: What is the definition of an endemic disease?

A. Disease affecting a large population
B. Disease occurring in excess of expected frequency
C. Disease occurring regularly in expected frequency (Correct Answer)
D. Disease occurring irregularly

Explanation: ***Disease occurring regularly in expected frequency*** - An **endemic disease** is consistently present in a population within a given geographic area at an **expected frequency**. - This implies that the disease is **always circulating** and has a baseline level of incidence. *Disease occurring in excess of expected frequency* - This definition describes an **epidemic**, where the disease occurrence is significantly higher than what is normally expected for that population. - While an endemic disease can become an epidemic, the core definition of endemic does not include an excess frequency. *Disease affecting a large population* - Affecting a large population is not the defining characteristic of an endemic disease; rather, it refers to the **scale** or **reach** of a disease. - A disease can affect a large population without being endemic, such as a widespread pandemic that is not regularly present in every affected region. *Disease occurring irregularly* - Irregular occurrence describes a more **sporadic** pattern of disease, where cases appear inconsistently and without a predictable frequency. - An **endemic disease** is characterized by its regular and predictable presence, even if the number of cases fluctuates within expected limits.

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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