Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1591: In a surgical post-op ward, a patient developed wound infection. Subsequently 3 other patients developed similar infections in the ward. What is the most effective way of preventing the spread of infection?

A. Fumigation of the ward
B. Wash OT instruments with 1% perchlorate
C. Proper hand washing of all ward personnel (Correct Answer)
D. Give IV antibiotics to all patients in the ward

Explanation: ***Proper hand washing of all ward personnel*** - **Hand hygiene** is the single most important and effective measure to prevent the spread of **healthcare-associated infections (HAIs)**, especially in a ward where multiple patients are affected. - It directly reduces the transmission of microorganisms from healthcare workers to patients and between patients. *Fumigation of the ward* - **Fumigation** is typically used for **terminal disinfection** or in situations involving highly resistant organisms or outbreaks, but it is not a routine or primary method for preventing day-to-day infection spread. - Its effectiveness is limited, and it can pose **health risks** to personnel and patients if not performed correctly, often requiring the ward to be vacated. *Wash OT instruments with 1% perchlorate* - This option focuses on the **sterilization of operating theater (OT) instruments**, which is crucial for surgical procedures but **irrelevant** to preventing the spread of wound infection within a general ward setting. - The problem describes a ward-based infection spread, not issues with surgical instrument sterility. *Give IV antibiotics to all patients in the ward* - **Prophylactic antibiotics** for all patients in a ward is generally **not recommended** as it can lead to **antibiotic resistance**, mask underlying infections, and cause adverse drug reactions. - Antibiotics should be prescribed judiciously based on specific indications and confirmed infections, not as a general preventive measure.

Question 1592: Action which halts the progression of a disease in early stage -

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

Explanation: ***Secondary prevention*** - This level of prevention focuses on **early detection** and **prompt intervention** to halt or slow the progression of a disease once it has started. - Examples include screening tests (e.g., mammograms, colonoscopies) and **early treatment** of identified conditions to prevent further deterioration. *Primordial prevention* - Aims to prevent the development of **risk factors** in the first place, often through broad social and environmental changes. - This occurs before any risk factors emerge and involves actions like promoting healthy lifestyles in children or creating policies for clean air. *Primary prevention* - Targets individuals or populations who are healthy but at risk for a disease, aiming to **prevent its occurrence**. - Examples include **vaccinations**, health education, and promoting exercise to avoid initial disease manifestation. *Tertiary prevention* - Focuses on minimizing the impact of an existing, established disease, preventing complications, and improving **quality of life**. - It involves **rehabilitation**, chronic disease management, and palliative care for individuals already suffering from the disease.

Question 1593: A study that examines individuals who have already contracted a disease to identify risk factors is called:

A. Control cohort
B. Cohort
C. Cross-sectional
D. Case control (Correct Answer)

Explanation: ***Case control*** - A **case-control study** specifically examines individuals who have already contracted the disease (**cases**) and compares them to those without the disease (**controls**). - The **cases** component directly addresses studying people who have already developed the disease to identify **risk factors** and **exposures** that led to the condition. - This is a **retrospective study design** that works backward from disease to exposure. *Control cohort* - A control cohort refers to a group of individuals who **do not have the disease or exposure** of interest and serve as a comparison group. - This is a component of studies, not a study type itself. - This option focuses on **healthy or unexposed individuals**, not those who have already contracted the disease. *Cohort* - A **cohort study** follows a group of individuals over time to observe who develops disease (**prospective**) or examines past exposures and outcomes (**retrospective**). - While it may include diseased individuals, its primary focus is on **disease incidence** and **temporal relationships**, starting from exposure and moving forward to disease outcome. *Cross-sectional* - A **cross-sectional study** examines disease and exposure status **simultaneously** at a single point in time. - It provides a **snapshot** of prevalence but does not specifically focus on examining those who have already contracted disease to identify risk factors. - It cannot establish **temporal relationships** between exposure and disease.

Question 1594: According to WHO definition, what is the epidemic threshold for meningococcal meningitis?

A. <2 per 1,00,000 population
B. >10 per 1,00,000 population (Correct Answer)
C. >100 per 1,00,000 population
D. 2-10 per 1,00,000 population

Explanation: ***>10 per 1,00,000 population*** - The World Health Organization (WHO) defines an epidemic threshold for meningococcal meningitis as an incidence of **more than 10 cases per 100,000 population per week** in an affected area. - This threshold is crucial for triggering an emergency response, such as mass vaccination campaigns, to control outbreaks of the disease. *<2 per 1,00,000 population* - An incidence of less than 2 cases per 100,000 population is typically considered a **very low endemic level** and does not meet the criteria for an epidemic. - This rate would signify routine surveillance rather than an urgent public health crisis for meningococcal meningitis. *>100 per 1,00,000 population* - While an incidence of 100 cases per 100,000 population would certainly indicate a severe epidemic, the **trigger threshold for intervention is much lower** than this. - Reaching this level would mean that the epidemic is already highly advanced and widespread, indicating a significant failure of earlier detection and response. *2-10 per 1,00,000 population* - An incidence in this range represents an **elevated endemic or early warning phase**, but it does not yet meet the official WHO epidemic threshold for meningococcal meningitis. - While it may prompt heightened surveillance and preparedness activities, it generally falls below the actionable threshold for full epidemic response.

Question 1595: Amongst the following, which carries the least chance of transmitting HIV infection:

A. Heterosexual Intercourse (Correct Answer)
B. Blood transfusion
C. IV drug abusers
D. Vertical transmission

Explanation: ***Heterosexual Intercourse*** - While a significant route globally, the per-act risk of transmission from an infected partner during **unprotected heterosexual intercourse** is relatively low compared to other high-risk exposures. - The risk is influenced by factors such as viral load, presence of STIs, and frequency of exposure, but on a per-exposure basis, it's generally considered lower than direct blood contact. *Blood transfusion* - Transfusion of HIV-infected blood carries an extremely **high risk of transmission**, approaching 100% due to the direct introduction of a significant viral load. - Due to rigorous screening of blood products in developed countries, this route is now rare but remains a major concern in regions with limited screening. *IV drug abusers* - Sharing of needles and syringes among **intravenous drug users** provides a direct pathway for blood-to-blood transmission, resulting in a very high risk of HIV infection. - Contaminated needles can retain viable virus for extended periods, facilitating efficient transmission when shared. *Vertical transmission* - **Mother-to-child transmission (MTCT)** can occur during pregnancy, childbirth, or breastfeeding, with rates varying significantly based on interventions. - Without intervention, the risk of MTCT can be as high as 25-30%, making it a highly efficient route of transmission from an infected mother to her child.

Question 1596: A pandemic of H1N1 is suspected when?

A. Community-level outbreaks in at least two WHO regions (Correct Answer)
B. Increased and sustained transmission in the general population
C. At least one laboratory confirmed H1N1 case
D. Sustained human-to-human transmission in multiple WHO regions

Explanation: ***Community-level outbreaks in at least two WHO regions*** - A pandemic is declared when there is evidence of **widespread geographical spread** with **community-level outbreaks** established in multiple regions. - According to WHO pandemic phase criteria, Phase 6 (pandemic) specifically requires **community-level outbreaks in at least two different WHO regions**, indicating that the virus has achieved sustained transmission at the population level across different geographical areas. - The emphasis on "community-level outbreaks" signifies established, ongoing transmission chains within communities, not just isolated cases or small clusters. *Increased and sustained transmission in the general population* - While this describes significant viral activity and is a component of pandemic criteria, it does not specify the **geographical spread requirement**. - This criterion could be met within a single country or region, qualifying as an **epidemic** rather than a pandemic. - A pandemic requires this transmission pattern to be present in **multiple WHO regions simultaneously**. *At least one laboratory confirmed H1N1 case* - A single confirmed case indicates the presence of the virus but does not suggest widespread or sustained transmission. - This would typically be classified as a **sporadic case** or imported case, not indicative of a pandemic. *Sustained human-to-human transmission in multiple WHO regions* - This option is very close to the correct answer and contains key pandemic elements: sustained transmission and geographical spread. - However, WHO's pandemic phase definition specifically emphasizes **"community-level outbreaks"** as the defining characteristic, which implies not just transmission, but established, self-sustaining transmission chains within communities. - The term "community-level outbreaks" is more specific and indicates a more advanced stage where the virus has become endemic within population groups, rather than just ongoing transmission which could still include primarily close-contact or household transmission. - Both options are technically correct, but Option A uses the **precise WHO terminology** from the pandemic phase definitions.

Question 1597: Chemoprophylaxis is __________ prevention.

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

Explanation: ***Primary*** - **Primary prevention** aims to prevent disease or injury before it ever occurs, often through interventions like vaccination or lifestyle changes. - **Chemoprophylaxis** involves administering medication to prevent a disease from developing, thus aligning with the goal of preventing the initial onset. *Secondary* - **Secondary prevention** focuses on early detection and prompt treatment of existing disease to prevent progression or complications. - This typically involves screening tests or early interventions once a condition has already begun. *Tertiary* - **Tertiary prevention** aims to reduce the impact of an ongoing illness or injury that has lasting effects, often through rehabilitation or management to improve quality of life. - This level of prevention occurs when a disease is already advanced and aims to minimize disability or recurrence. *Primordial* - **Primordial prevention** is the earliest stage of prevention, targeting underlying social and environmental conditions that contribute to health risks, often at a population level. - It focuses on preventing the emergence of risk factors themselves, rather than preventing the disease in individuals.

Question 1598: Infectious agent is transmitted to susceptible host from -

A. Reservoir
B. All of these (Correct Answer)
C. Carrier and Case
D. Source

Explanation: ***All of these*** - In epidemiology, an infectious agent can be transmitted to a susceptible host from **multiple origins** in the chain of infection. - **Source**: The person, animal, object, or substance from which an infectious agent passes immediately to a host (e.g., contaminated food, infected person, contaminated water). - **Reservoir**: The natural habitat where the infectious agent normally lives and multiplies (humans, animals, or environment) and from which it can be transmitted directly or indirectly to susceptible hosts. - **Carrier and Case**: Both are infected individuals who can directly transmit the agent - carriers harbor the pathogen without symptoms, while cases have clinical disease. - All these terms represent different aspects of where transmission originates, making **"All of these"** the most complete and accurate answer. *Carrier and Case* - While carriers and cases are important transmitters, this option is too narrow as it excludes other valid sources and reservoirs of transmission. - This would only be correct if the question specifically asked about transmission from infected **humans** only. *Source* - Alone, this is correct but incomplete, as it doesn't encompass the full epidemiological framework. - Sources include reservoirs, carriers, and cases. *Reservoir* - Alone, this is also correct but incomplete. - Reservoirs can be sources of infection, and infected humans (carriers/cases) can serve as reservoirs for human-adapted pathogens.

Question 1599: All are modifiable risk factors except

A. Weight
B. Cigarette smoking
C. Diabetes
D. Personality (Correct Answer)

Explanation: ***Personality*** - **Personality traits**, such as Type A behavior, are **not directly modifiable** through lifestyle changes or medical interventions. - While coping mechanisms can be learned, the underlying personality structure is generally considered a **non-modifiable risk factor** for various health outcomes. *Weight* - **Weight** is a **modifiable risk factor** that can be changed through diet, exercise, and other lifestyle interventions. - Maintaining a **healthy weight** reduces the risk of numerous diseases, including cardiovascular disease and diabetes. *Cigarette smoking* - **Cigarette smoking** is a highly **modifiable risk factor** that can be completely eliminated by quitting. - Smoking cessation significantly reduces the risk of cancer, heart disease, and respiratory illnesses. *Diabetes* - **Established diabetes** is considered a **non-modifiable risk factor** for cardiovascular complications and other diseases in epidemiological classification. - While the **risk of developing diabetes** can be modified through lifestyle interventions, and **glycemic control** can be managed, the disease state itself once present is categorized as non-modifiable. - However, **Personality** is the more clearly non-modifiable factor among the options, as it represents an inherent trait rather than an acquired condition.

Question 1600: Mosquitoes whose eggs are found attached to aquatic plants are

A. Culex
B. Mansonia (Correct Answer)
C. Aedes
D. Anopheles

Explanation: ***Mansonia*** - *Mansonia* mosquitoes are unique in that their **eggs are laid individually and attached to the undersurface of floating aquatic plants**. - The larvae and pupae also attach to these plants using specialized siphons to obtain oxygen, instead of rising to the water surface. *Culex* - *Culex* mosquitoes lay their **eggs in rafts on the surface of still water**, not attached to aquatic plants. - The larvae and pupae are free-swimming and obtain oxygen directly from the water surface. *Aedes* - *Aedes* mosquitoes typically lay **single eggs on moist surfaces just above the water line** in containers or tree holes, which hatch when flooded. - Their eggs are not attached to aquatic plants in the water. *Anopheles* - *Anopheles* mosquitoes lay **single, boat-shaped eggs directly on the water surface**, each with floats on either side. - These eggs are not attached to aquatic plants and float freely on the water.

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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