Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1611: Communicability of disease is assessed by

A. Incubation period
B. Serial interval
C. Secondary attack rate (Correct Answer)
D. Generation time

Explanation: ***Secondary attack rate*** - The **secondary attack rate** directly measures the proportion of susceptible individuals who become infected after exposure to a primary case within a household or other closed setting, making it a direct indicator of **communicability**. - It quantifies the spread of disease from an existing case to close contacts, specifically reflecting how easily a pathogen transmits. *Incubation period* - The **incubation period** is the time from exposure to a pathogen to symptom onset, which indicates the latency of disease, not its communicability. - While it helps in case tracing and surveillance, it doesn't directly measure how easily the disease spreads from one person to another. *Serial interval* - The **serial interval** is the time between symptom onset in an infected person and symptom onset in a person infected by them; it reflects the pace of an epidemic but doesn't quantify transmissibility. - While related to transmission dynamics, it's not a direct measure of how likely an exposed person is to get sick. *Generation time* - **Generation time** is the average time between infection in a primary case and infection in a secondary case, providing a measure of the pathogen's intrinsic rate of spread. - It is similar to serial interval but focuses on infection times rather than symptom onset, and like the serial interval, it contributes to understanding disease dynamics but isn't as direct a measure of communicability as the secondary attack rate.

Question 1612: In which of the following infections is the mosquito the main vector?

A. Yellow fever (Correct Answer)
B. Leprosy
C. Cholera
D. Hepatitis - A

Explanation: ***Yellow fever*** - Yellow fever is a **viral hemorrhagic fever** transmitted by infected **_Aedes aegypti_ mosquitoes**. - The disease causes symptoms ranging from mild fever to severe illness with **jaundice** and internal **bleeding**. *Leprosy* - Leprosy is a **chronic bacterial infection** caused by **_Mycobacterium leprae_**. - It is primarily transmitted through **respiratory droplets** from prolonged close contact with an infected person. *Cholera* - Cholera is an **acute diarrheal disease** caused by infection of the intestine with **_Vibrio cholerae_ bacteria**. - It is typically spread through **contaminated water** or food sources. *Hepatitis - A* - Hepatitis A is a **viral liver disease** caused by the **Hepatitis A virus (HAV)**. - It is primarily transmitted via the **fecal-oral route**, often through contaminated food or water.

Question 1613: How many guinea worm cases were identified globally in the year 2007?

A. 0
B. 4000
C. 9
D. 2000 (Correct Answer)

Explanation: ***2000*** - Approximately **2,000 cases of guinea worm disease (dracunculiasis)** were reported globally in 2007, representing a significant milestone in the eradication campaign. - This figure demonstrates a dramatic reduction from over **75,000 cases in 2000**, reflecting the success of the Carter Center and WHO Guinea Worm Eradication Program. - The decline was achieved through community-based interventions including health education, provision of safe drinking water, and case containment strategies. *0* - Guinea worm disease had not yet been eradicated by 2007; cases continued to occur primarily in sub-Saharan Africa. - While zero cases was the ultimate goal, substantial work remained to achieve complete eradication. *4000* - This overestimates the global case count in 2007. - The actual number was approximately **half of this figure**, showing that interventions had progressed beyond this level. *9* - This significantly underestimates the remaining cases in 2007. - Single-digit annual case counts were not achieved until the mid-2010s, when only a handful of endemic countries remained.

Question 1614: Which of the following diseases is characterized by propagative transmission?

A. Filaria
B. Plague
C. Malaria
D. All of the options (Correct Answer)

Explanation: ***All of the options*** **Propagative transmission** is a type of biological transmission where the pathogen undergoes **multiplication and/or development** within the vector before being transmitted to a new host. **All three diseases exhibit propagative transmission:** - ***Plague***: *Yersinia pestis* multiplies extensively in the gut of the flea (*Xenopsylla cheopis*). The bacteria form a biofilm that blocks the proventriculus, causing the flea to regurgitate bacteria into the bite wound during feeding. - ***Malaria***: *Plasmodium* species undergo **sporogony** (sexual reproduction and development) in the *Anopheles* mosquito. The parasite develops from gametocytes → zygote → ookinete → oocyst → sporozoites over 10-14 days. This is **cyclopropagative transmission**. - ***Filaria***: *Wuchereria bancrofti* undergoes larval development in mosquitoes (*Culex* species). The microfilariae develop through three larval stages (L1 → L2 → L3) in the mosquito's thoracic muscles before becoming infective. This is also **cyclopropagative transmission**. **Key Concept**: In propagative transmission, there is an **extrinsic incubation period** during which the pathogen develops in the vector, distinguishing it from mechanical transmission where simple transfer occurs without multiplication or development.

Question 1615: In a UK study, it was found that there were more deaths from Asthma than the sales of Anti-asthma drugs would suggest. This is an example of

A. Ecological study (Correct Answer)
B. Experimental study
C. Case-control study
D. Cohort study

Explanation: ***Ecological study*** - An **ecological study** analyzes data at the population or group level rather than at the individual level. - In this scenario, the comparison of asthma deaths (population-level data) with anti-asthma drug sales (another population-level aggregate) for an entire country (UK) is characteristic of an ecological study. - This represents an **ecological correlation** where aggregate data is used to identify patterns at the population level. *Experimental study* - An **experimental study** involves direct intervention by the researcher to control variables and assign subjects to different groups (e.g., treatment vs. control) to assess cause-and-effect. - This study design does not involve any intervention or randomization; it's an observational analysis of existing population data. *Case-control study* - A **case-control study** compares individuals with a disease (cases) to individuals without the disease (controls) to identify risk factors at the individual level. - The given scenario is not comparing individuals but rather aggregate data from a population. *Cohort study* - A **cohort study** follows a group of individuals (a cohort) over time to observe the incidence of disease or outcomes in relation to specific exposures. - The scenario describes a cross-sectional comparison of population-level data at a specific point or period, not a longitudinal follow-up of individuals.

Question 1616: Aedes aegypti index at airport -

A. 1
B. 0
C. 1-2
D. <1 (Correct Answer)

Explanation: ***Correct: <1 (Less than 1)*** - The **Aedes aegypti index** at an airport should ideally be **less than 1** to prevent the introduction and spread of mosquito-borne diseases like dengue, yellow fever, and Zika. - A low index indicates effective mosquito control measures are in place, minimizing the risk of disease transmission. - This is the **standard recommended by WHO** and International Health Regulations (IHR) for airports and ports. *Incorrect: 1* - An index of **1** suggests that **1% of the premises** surveyed have Aedes aegypti larvae or pupae. - While seemingly low, this percentage could still pose a risk for disease transmission, especially in a high-traffic area like an airport. - This exceeds the acceptable threshold for vector control at international points of entry. *Incorrect: 0* - An index of **0** would mean no Aedes aegypti breeding sites were found, indicating an ideal but often **practically unachievable state** due to environmental factors and constant human activity. - While desirable, maintaining a zero index might be **economically and operationally challenging** in a large, dynamic environment like an airport. *Incorrect: 1-2* - An index of **1-2** indicates that 1% to 2% of premises have breeding sites, which is considered an **unacceptable risk** for an airport. - At this level, there is a **significant potential** for the introduction and establishment of Aedes-borne diseases, violating international health standards.

Question 1617: The disability adjusted life years (DALYs) lost due to neuropsychiatric disorders are highest in -

A. Panic disorders
B. Obsessive compulsive disorder
C. Bipolar affective disorders
D. Unipolar depressive disorders (Correct Answer)

Explanation: ***Unipolar depressive disorders*** - **Unipolar depressive disorders** are the leading cause of DALYs lost among neuropsychiatric conditions globally. - This is due to their **high prevalence**, **early age of onset**, and significant impact on **functional capacity** and quality of life. *Panic disorders* - While panic disorders significantly impair an individual's quality of life, their **prevalence** and **disability burden** are generally lower than that of unipolar depressive disorders. - They tend to cause episodic, intense distress rather than chronic, pervasive functional impairment to the same extent as severe depression. *Obsessive compulsive disorder* - **OCD** can be severely disabling, but its **prevalence** is lower than that of unipolar depressive disorders. - The impact on DALYs, while substantial for affected individuals, does not reach the global burden attributed to depression. *Bipolar affective disorders* - **Bipolar affective disorders** contribute significantly to DALYs due to their chronic nature and severe episodes of mood disturbance. - However, their **prevalence** is lower compared to unipolar depressive disorders, resulting in a lower overall DALY burden globally.

Question 1618: Disease not under integrated disease surveillance project is?

A. Herpes Zoster (Correct Answer)
B. Meningoencephalitis
C. TB
D. Cholera

Explanation: ***Herpes Zoster*** - **Herpes Zoster**, also known as shingles, is a viral disease that is typically not included in the list of diseases under routine surveillance by the Integrated Disease Surveillance Project (IDSP) in many regions. - The IDSP primarily focuses on diseases with **epidemic potential** or high public health impact for early detection and rapid response. *Meningoencephalitis* - **Meningoencephalitis** (inflammation of the brain and meninges) is a serious condition with epidemic potential, making it a key disease for surveillance under projects like IDSP. - Early detection of clusters can help prevent widespread outbreaks and manage severe neurological outcomes. *TB* - **Tuberculosis (TB)** is a major public health concern due to its high prevalence, chronic nature, and potential for transmission, especially drug-resistant forms. - It is consistently included in surveillance programs like IDSP for consistent monitoring, case finding, and treatment adherence. *Cholera* - **Cholera** is an acute diarrheal disease with high epidemic potential due to rapid transmission, particularly in areas with poor sanitation. - It is a critical disease for surveillance to enable quick identification of outbreaks, implementation of control measures, and prevention of mass fatalities.

Question 1619: SET centers are established if the prevalence of leprosy is (per 1000 population):

A. 10
B. 5–10
C. 1–5 (Correct Answer)
D. 0.5–1

Explanation: ***1–5*** - **SET (Survey, Education, Treatment) centers** are established in areas where the prevalence of leprosy is **1 to 5 cases per 1000 population**. - This prevalence indicates a moderate endemicity, requiring a focused approach for case detection, health education, and timely treatment to control the disease spread. *10* - A prevalence of **10 cases per 1000 population** is considered very high, suggesting a more widespread disease burden that might necessitate broader public health interventions rather than just SET centers. - This level might indicate a need for more intensive screening and mass treatment strategies. *5–10* - A prevalence of **5 to 10 cases per 1000 population** is also relatively high, usually prompting more aggressive control measures beyond the standard SET center approach. - Such high prevalence often points to areas requiring more advanced intervention strategies. *0.5–1* - A prevalence of **0.5 to 1 case per 1000 population** is considered low, indicating that leprosy is nearing elimination as a public health problem. - In such scenarios, integration of leprosy services into general health services or sentinel surveillance might be sufficient, rather than establishing dedicated SET centers.

Question 1620: Quarantine duration is primarily based on:

A. Generation time
B. Serial interval
C. Maximum incubation (Correct Answer)
D. Minimum incubation period

Explanation: ***Maximum incubation*** - Quarantine duration is set to cover the **maximum incubation period** of a disease to ensure that individuals who are infected but asymptomatic eventually develop symptoms and can be isolated. - This prevents potentially infected individuals from transmitting the disease to others after their isolation period ends. *Generation time* - **Generation time** is the average time between an individual becoming infected and that individual infecting others. - While related to transmission, it's not the primary determinant for the **maximum duration an asymptomatic person could be infectious** without showing symptoms, which is the focus of quarantine. *Serial interval* - The **serial interval** is the time between symptom onset in an infected person and symptom onset in a person they infect. - Like generation time, it describes the pace of an epidemic but doesn't define the **outer limit of when an infected person might show symptoms** to determine quarantine length. *Minimum incubation period* - The **minimum incubation period** is the shortest time between exposure and symptom onset. - Relying on the minimum incubation period would lead to a quarantine that is too short, as many individuals would still be in their **asymptomatic infectious phase** after quarantine ends.

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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