Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1721: Which of the following correctly describes the components of the epidemiological triad?

A. Agent, host, environment (Correct Answer)
B. Agent, disease, vector
C. Time, place, person
D. Disease, prevention, treatment

Explanation: **Agent, host, environment** * The **epidemiological triad** is a classic model that describes the interrelationships contributing to disease development. * It consists of the **agent** (the causative factor), the **host** (the organism contracting the disease), and the **environment** (extrinsic factors influencing exposure and susceptibility). * *Time, place, person (descriptive epidemiology)* * **Time, place, and person** are key components of **descriptive epidemiology**, used to characterize disease patterns. * While important for understanding disease distribution, they do not represent the causative interconnectedness of the epidemiological triad. * *Disease, prevention, treatment (healthcare process)* * **Disease, prevention, and treatment** describe aspects of the healthcare process and public health interventions. * They are not the fundamental components used to explain the *occurrence* of disease as modeled by the epidemiological triad. * *Agent, disease, vector (lacks host and environmental components)* * This option includes the **agent** and a **vector** (which is a type of environmental factor or can be considered part of the agent's transmission). * However, it misses the crucial component of the **host** and fully encompassing the broader **environment**.

Question 1722: What is the primary purpose of taking sewer swabs in public health?

A. Active typhoid cases in the community
B. Active cholera cases in the community
C. Typhoid carriers in the community (Correct Answer)
D. Cholera carriers in the community

Explanation: ***Typhoid carriers in the community*** - Sewer swabs are primarily used to detect the presence of **Salmonella Typhi** in sewage, indicating the presence of **asymptomatic carriers** shedding the bacteria. - This method helps identify populations where **typhoid fever** may silently spread or persist due to chronic carriers. *Active typhoid cases in the community* - While sewer swabs can indirectly indicate **active cases** due to increased shedding, their primary purpose is to identify **carriers** who might not be exhibiting symptoms. - **Clinical diagnosis** and **stool culture** from symptomatic individuals are more direct methods for identifying active typhoid cases. *Active cholera cases in the community* - Sewer swabs *can* detect **Vibrio cholerae**, the bacterium causing cholera, but this is not their primary use, especially when targeting **typhoid surveillance**. - **Cholera** outbreaks typically prompt targeted **water sample testing** and clinical surveillance due to their rapid onset and severity. *Cholera carriers in the community* - Similar to active cases, while possible to detect **Vibrio cholerae**, sewer swabs are not the primary tool specifically for identifying **cholera carriers**. - **Cholera carriers** are less common and their detection is usually part of broader environmental surveillance during or after an outbreak.

Question 1723: Which of the following is the best indicator for assessing the rate of new cases of disease occurring in a population?

A. Proportional mortality rate
B. Crude death rate
C. Cause specific death rate
D. Incidence (Correct Answer)

Explanation: ***Incidence*** - **Incidence** measures the rate at which **new cases** of a disease occur in a population over a specified period, making it the primary indicator for assessing the **occurrence of new disease**. - It is essential for understanding disease dynamics, identifying outbreaks, and evaluating the **risk** of acquiring a disease in a population. - High incidence indicates active transmission or ongoing exposure to risk factors. *Crude death rate* - The **crude death rate** measures all deaths in a population regardless of cause, serving as a general indicator of overall mortality. - It does not specifically measure **disease occurrence** or distinguish between different causes of death. - Not useful for tracking new cases of disease in the population. *Cause specific death rate* - The **cause-specific death rate** measures deaths due to a particular disease, reflecting the **fatal outcomes** only. - It does not capture the **incidence** of disease or account for non-fatal cases. - Limited to mortality data and misses the broader picture of disease occurrence. *Proportional mortality rate* - The **proportional mortality rate** indicates what proportion of all deaths are due to a specific cause. - It is a **relative measure** that depends on the total number of deaths from all causes. - Does not reflect the **absolute risk** or rate of new disease occurrence in the population.

Question 1724: Under which condition is screening IMPOSSIBLE (most fundamental criterion)?

A. Prevalence of disease is low
B. Life expectancy cannot be prolonged by early diagnosis
C. Diagnostic test is not available
D. Diseases with no latent period (Correct Answer)

Explanation: ***Diseases with no latent period*** - This is the **MOST FUNDAMENTAL criterion** for screening - without a latent (presymptomatic) period, screening is **IMPOSSIBLE**, not just inefficient. - Screening is designed to detect diseases in their **presymptomatic phase** to allow for early intervention. - If symptoms appear immediately upon disease onset, there is **no detectable pre-clinical phase** to screen for. - This is a **Wilson-Jungner criterion** - the condition must have a recognizable latent or early symptomatic stage. *Prevalence of disease is low* - Low prevalence makes screening **inefficient and not cost-effective** due to low positive predictive value. - However, screening is still **theoretically possible**, just not recommended from a public health perspective. - This is an economic/efficiency criterion, not a fundamental feasibility criterion. *Life expectancy cannot be prolonged by early diagnosis* - If early treatment doesn't improve outcomes, screening lacks **benefit** but is still technically possible. - This relates to the **effectiveness of available treatment**, not the feasibility of screening itself. - Screening without treatment benefit violates the criterion that "there should be an accepted treatment for patients with recognized disease." *Diagnostic test is not available* - Without a suitable test, screening **cannot be performed**, but this is a **resource issue**, not a disease characteristic. - Once a test is developed, screening becomes possible. - The "no latent period" criterion is more fundamental as it relates to the **natural history of the disease** itself.

Question 1725: NFHS-3 was conducted in?

A. 1992-93
B. 1998-99
C. 2005-06 (Correct Answer)
D. 2009-10

Explanation: ***2005-06*** - The **National Family Health Survey (NFHS-3)** was indeed conducted during the period of **2005-2006**. - This survey provided crucial data on health and family welfare indicators across India. *1992-93* - This period corresponds to the **National Family Health Survey (NFHS-1)**, the first in the series. - It established baseline data for various health and demographic parameters in India. *1998-99* - This time frame marks the conduction of the **National Family Health Survey (NFHS-2)**. - NFHS-2 provided updated information and trends compared to NFHS-1. *2009-10* - While a significant health survey, this period does not correspond to NFHS-3. No NFHS survey was conducted then.

Question 1726: Which group classification does a state belong to if the prevalence of HIV infection in antenatal women is reported to be less than 1% and in high-risk populations is reported to be less than 5%?

A. Group A
B. Group B
C. Group D
D. Group C (Correct Answer)

Explanation: ***Group C*** - This classification is used when the **prevalence of HIV infection** in **antenatal women** is **less than 1%** and in **high-risk populations** is **less than 5%**. - These criteria indicate a relatively **low-level epidemic** or a concentrated epidemic among specific risk groups. *Group A* - This group typically refers to states or regions where the **HIV epidemic is generalized**, meaning prevalence is high in the general adult population (>1%). - The criteria for Group A are much higher than described in the question, suggesting widespread transmission beyond specific risk groups. *Group B* - Group B usually describes a situation where the **HIV epidemic is concentrated** in specific **high-risk groups**, but still at a higher prevalence than Group C (e.g., >5% in high-risk populations). - The antenatal prevalence might still be relatively low, but the prevalence in specific at-risk groups would exceed 5%. *Group D* - This classification is not a standard category in the common epidemiological grouping of HIV epidemics. - The established classifications generally include categories like low-level, concentrated, and generalized epidemics, which correspond to the other options.

Question 1727: A study is conducted using people who volunteer to participate. Which type of bias may occur?

A. Selection bias (Correct Answer)
B. Hawthorne effect bias
C. Berkson's bias
D. Observer bias

Explanation: ***Selection bias*** - **Selection bias** occurs when participants for a study are not chosen randomly, leading to groups that are not comparable. - In this scenario, individuals who **volunteer** for a randomized study may differ systematically from those who do not, affecting the generalizability of results. *Hawthorne effect bias* - The **Hawthorne effect** is a type of reactivity in which individuals modify an aspect of their behavior in response to their awareness of being observed. - This bias is related to the **observational setting** and the human response to being studied, rather than the initial selection of participants. *Berkson's bias* - **Berkson's bias** is a form of selection bias that results from differential rates of hospital admission for different diseases. - It arises in studies using hospitalized patients, where the **exposure-disease relationship** might be distorted compared to the general population. *Observer bias* - **Observer bias** (also known as ascertainment bias) occurs when researchers' expectations, beliefs, or preconceptions influence the observation or recording of data. - This bias relates to the **measurement or assessment of outcomes** by investigators, not the recruitment of study participants.

Question 1728: Which method is primarily used to detect cases that may not be identified through other surveillance techniques?

A. Active surveillance (Correct Answer)
B. Passive surveillance
C. Sentinel surveillance
D. Prevalence rate

Explanation: ***Active surveillance*** - This method involves **proactive efforts by public health officials** to identify cases by directly contacting healthcare providers, visiting facilities, and actively searching for unreported cases. - It is specifically designed to **detect cases that may be missed** by passive reporting systems due to underreporting, lack of awareness, or incomplete reporting. - While resource-intensive, it ensures **comprehensive case detection** and is the gold standard for identifying all cases of diseases under surveillance, particularly during outbreak investigations. *Passive surveillance* - This method relies on **voluntary reporting** by healthcare providers to public health authorities. - It is inexpensive but often **misses cases** due to underreporting, making it the system that active surveillance is designed to supplement. *Sentinel surveillance* - This method uses **carefully selected reporting sites** (hospitals, clinics, or practitioners) to monitor disease trends and provide early warning signals. - It is designed for **monitoring specific diseases** efficiently and detecting emerging patterns, not primarily for finding cases missed by other methods. - Useful for resource-limited settings to track trends without comprehensive reporting. *Prevalence rate* - This is a **descriptive epidemiological measure** indicating the proportion of a population with a disease at a given time. - It is not a surveillance method but rather a **statistical measure** used to assess disease burden.

Question 1729: What type of prevention does screening represent in public health?

A. Primordial prevention
B. Secondary prevention (Correct Answer)
C. Primary prevention
D. Tertiary prevention

Explanation: ***Secondary prevention*** - **Screening** aims to **detect disease early** in asymptomatic individuals, allowing for prompt intervention and preventing disease progression. - This aligns with secondary prevention's goal of **reducing the impact of a disease** once it has occurred or is in its early stages. *Primordial prevention* - Focuses on **preventing the emergence of risk factors** for disease in the first place, often through broad public health policies. - It targets the entire population or specific groups to **avoid the development of unhealthy lifestyles or environmental conditions**. *Primary prevention* - Aims to **prevent the onset of disease** in healthy individuals by addressing risk factors or providing protective measures. - Examples include **vaccination** to prevent infectious diseases or promoting **healthy diets** to prevent cardiovascular disease. *Tertiary prevention* - Involves measures to **reduce the negative impact of an already established disease** by improving quality of life, reducing disability, and preventing complications. - This includes **rehabilitation, pain management**, and support groups for individuals living with chronic conditions.

Question 1730: What is the criterion for blindness as defined in India?

A. Visual acuity less than 3/60
B. Visual acuity less than 6/60 (Correct Answer)
C. Visual acuity less than 12/60
D. Visual acuity less than 18/60

Explanation: ***Visual acuity less than 6/60*** - In India, **blindness** is officially defined as a visual acuity of **less than 6/60** in the better eye with best possible correction, or a visual field constriction to 20 degrees or worse. - This definition is crucial for determining eligibility for **disability benefits** and access to vision rehabilitation services under the Persons with Disabilities Act. - This threshold represents the minimum criterion for legal blindness in India. *Visual acuity less than 3/60* - A visual acuity of less than 3/60 represents **severe blindness (Category 3)**, which is **worse than the minimum threshold** of 6/60. - This level of vision loss **does qualify as legal blindness** in India, representing a more profound degree of visual impairment. - While 6/60 is the defining threshold, 3/60 indicates even more severe vision loss. *Visual acuity less than 12/60* - Visual acuity less than 12/60 but better than 6/60 indicates **low vision** or moderate visual impairment, but it does **not** meet the criteria for legal blindness in India. - This level is categorized as low vision, where individuals may still benefit from magnifiers and other visual aids. - Such individuals retain significant functional vision for many tasks. *Visual acuity less than 18/60* - A visual acuity of less than 18/60 but better than 6/60 is considered **mild to moderate visual impairment** or low vision, but it does not qualify as legal blindness. - Individuals with this vision level typically retain considerable functional vision, although they may experience difficulties with certain tasks requiring fine detail. - This level may qualify for low vision services but not disability certification for blindness.

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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