Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 581: What is the recommended mesh size for mosquito nets to effectively prevent mosquito bites?

A. 50 holes per square inch
B. 156 holes per square inch (Correct Answer)
C. 100 holes per square inch
D. 200 holes per square inch

Explanation: ***156 holes per square inch*** - This mesh size, equivalent to a **hole dimension of 1.5mm x 1.5mm**, is recommended by the **WHO** for insecticide-treated nets (ITNs) to effectively prevent mosquito entry. - It provides a balance between sufficient air circulation and preventing even smaller mosquito species from passing through. *50 holes per square inch* - This mesh size is too large and would allow **smaller mosquito species** to easily pass through, rendering the net ineffective. - It would not provide adequate **protection** against mosquito bites and disease transmission. *100 holes per square inch* - While better than 50 holes, this mesh size might still be insufficient to block all mosquito species, especially very small ones. - It does not meet the **WHO guidelines** for optimal protection. *200 holes per square inch* - Although this size would effectively block mosquitoes, it might excessively restrict **airflow**, making the net uncomfortable to sleep under in warm climates. - Higher mesh counts can also lead to **increased production costs** and potential issues with durability.

Question 582: What is the most common source of Diphtheria?

A. Infected environment
B. Carrier (Correct Answer)
C. Infected individual
D. None of the options

Explanation: ***Carrier*** - **Carriers** (asymptomatic individuals harboring *Corynebacterium diphtheriae*) are the **most common source** of diphtheria transmission. - Carriers outnumber symptomatic cases by a **ratio of 10:1 or more** in the community. - They shed bacteria through **respiratory droplets for weeks to months** without showing symptoms, making them difficult to identify and isolate. - Carriers form the **primary reservoir** that maintains diphtheria transmission in populations, especially in areas with suboptimal immunization coverage. - This is a fundamental epidemiological principle emphasized in Community Medicine. *Infected individual* - While symptomatic infected individuals do transmit diphtheria, they are **less common** as a source compared to carriers. - Symptomatic cases are more likely to be **identified, isolated, and treated** quickly, limiting their transmission potential. - They represent the "tip of the iceberg" in diphtheria epidemiology. *Infected environment* - *Corynebacterium diphtheriae* does not survive for extended periods outside the human host. - Environmental transmission is **extremely rare** and not a significant mode of spread. - Diphtheria is primarily transmitted through **respiratory droplets** (person-to-person contact). *None of the options* - Incorrect, as **carrier** is clearly the most common source of diphtheria.

Question 583: Range of flight of Aedes mosquito is?

A. 1 km
B. Less than 100 m
C. 400 m (Correct Answer)
D. 10 km

Explanation: ***400 m*** - *Aedes* mosquitoes have a **typical flight range of up to 400 meters** from their breeding sites, which is well-established in vector control literature. - This flight range is a critical factor in planning **control measures and source reduction strategies**, as interventions need to cover a 400m radius around cases. - Most *Aedes aegypti* prefer to stay within **50-100 meters** but can disperse up to 400m when searching for blood meals or oviposition sites. *Less than 100 m* - While many *Aedes* mosquitoes do stay within **100 meters** of their breeding sites under normal conditions, this represents their **preferred range** rather than maximum capability. - The **maximum flight range** extends beyond this distance, making this answer too restrictive for vector control planning. *1 km* - A flight range of **1 km** exceeds the typical dispersal distance for *Aedes* mosquitoes under normal circumstances. - While occasional long-distance dispersal has been documented, this is not the standard flight range used in epidemiological planning. *10 km* - This distance is far too great for *Aedes* mosquitoes, which are relatively weak fliers. - Such long distances would require **passive transport** (vehicles, wind) rather than active flight.

Question 584: What was the color of the box containing drugs for the treatment of Category I tuberculosis (TB) under the DOTS program?

A. Blue
B. Green
C. Red
D. Yellow (Correct Answer)

Explanation: ***Yellow*** - The **yellow box** was designated for **Category I TB drugs** under the **DOTS (Directly Observed Treatment, Short-course)** strategy. - Category I treated **newly diagnosed sputum smear-positive pulmonary TB**, severely ill smear-negative cases, and severe extrapulmonary TB. - **Note:** India transitioned from category-based to **weight-based TB treatment** in 2012 under NTEP (formerly RNTCP). This color-coded system is now historical. *Red* - The **red box** was used for **Category II TB treatment**, covering **retreatment cases** (relapse, treatment failure, or treatment after default). - These regimens included additional drugs like streptomycin with different durations compared to Category I. *Blue* - The **blue box** was used for **Category III TB treatment** in the DOTS program. - Category III covered new smear-negative pulmonary TB cases and less severe extrapulmonary TB. *Green* - The **green box** was not part of the standard category-based DOTS framework for TB drug distribution. - The three main categories used yellow, red, and blue color-coding to prevent dispensing errors.

Question 585: Which insecticide is commonly used for insecticide-treated bed nets (ITBN) in malaria control?

A. Deltamethrin (Correct Answer)
B. Malathion
C. Fenitrothion
D. Lindane

Explanation: ***Deltamethrin*** - **Deltamethrin** is a synthetic pyrethroid, widely favored for its **low mammalian toxicity** and high efficacy against mosquitoes, making it ideal for ITBNs. - Its **residual action** ensures long-lasting protection against mosquito bites, crucial for effective malaria prevention. *Malathion* - **Malathion** is an organophosphate insecticide and is generally used for **outdoor mosquito control** as a spray, but not typically impregnated into bed nets due to its odor and faster degradation. - It has a higher **acute toxicity** profile compared to pyrethroids, making it less suitable for direct prolonged human contact via bed nets. *Lindane* - **Lindane** (gamma-hexachlorocyclohexane) is an organochlorine insecticide which has been largely **phased out** for public health use due to its persistence in the environment and concerns about its potential neurotoxicity. - It is currently **not recommended** for ITBNs given environmental and health concerns as well as the availability of safer alternatives. *Fenitrothion* - **Fenitrothion** is another organophosphate insecticide primarily used in **agriculture** and for indoor residual spraying (IRS), but it is not commonly used for ITBNs. - Its **higher volatility** and less favorable safety profile compared to pyrethroids limit its use in materials that have direct and prolonged contact with people.

Question 586: In which disease is a healthy carrier commonly seen?

A. Measles
B. Rubella
C. Meningococcal meningitis (Correct Answer)
D. Influenza

Explanation: ***Meningococcal meningitis*** - A significant proportion of the population can carry *N. meningitidis* in their **nasopharynx** without developing symptoms, serving as a reservoir for transmission. - This **asymptomatic carriage** is crucial for the spread and persistence of the disease in communities. *Measles* - Measles is highly contagious and typically causes **clear symptoms** in infected individuals; the concept of a healthy, asymptomatic carrier is not relevant. - Individuals with measles are infectious during the **prodromal phase** and until several days after rash onset. *Rubella* - Rubella, while often mild, does not typically involve a **healthy carrier state** where individuals harbor and transmit the virus without symptoms. - Infected individuals usually exhibit a **rash** and mild symptoms, and are contagious during that period. *Influenza* - While individuals can have **asymptomatic or very mild influenza infections**, they are not generally considered **healthy carriers** in the same way as meningococcal disease. - Asymptomatic influenza shedding is usually for a **shorter duration** compared to the prolonged carriage seen with *N. meningitidis*.

Question 587: Varicella zoster virus infection is more likely to occur in which of the following months?

A. March (Correct Answer)
B. August
C. October
D. November

Explanation: ***March*** - Varicella-zoster virus (VZV) infections, particularly **chickenpox**, show a peak incidence during **late winter and spring months**. - This seasonality is attributed to changes in human behavior and environmental factors that facilitate transmission. *August* - **August** is typically a summer month in many regions, and VZV infections are less common during warmer periods. - Reduced indoor crowding and increased exposure to UV light may contribute to lower transmission rates. *October* - While October marks the beginning of autumn, it generally precedes the peak season for VZV infections. - Transmission rates start to increase but are usually not as high as in late winter or early spring. *November* - November, late autumn or early winter, sees an increase in respiratory and viral infections due to colder weather and increased indoor gatherings. - However, the peak incidence for VZV is typically observed a few months later, in late winter and early spring.

Question 588: What is the median incubation period in the context of infectious diseases?

A. Time from exposure to development of symptoms in 50% of cases (Correct Answer)
B. The longest time from exposure to development of symptoms in all cases
C. The shortest time from exposure to development of symptoms in all cases
D. Not applicable to any infectious disease

Explanation: ***Time from exposure to development in 50% of cases*** - The **median incubation period** is a statistical measure representing the point at which half of the exposed individuals would have developed symptoms. - This provides a more **robust central tendency** compared to minimum or maximum values, as it's less affected by outliers. *The longest time from exposure to development of symptoms in all cases* - This describes the **maximum incubation period**, which is useful for setting the complete isolation or monitoring period but not for predicting the typical onset. - It does not represent the central tendency or the expected time of symptom onset for most individuals. *The shortest time from exposure to development of symptoms in all cases* - This refers to the **minimum incubation period**, indicating the earliest possible onset of symptoms after exposure. - While important for immediate risk assessment, it doesn't characterize the typical duration for the majority of affected individuals. *Not applicable to any infectious disease* - The concept of an **incubation period is fundamental** to infectious diseases, defining the time between exposure to a pathogen and the first appearance of symptoms. - The median incubation period is a **standard epidemiological measure** used to understand disease progression and inform public health interventions.

Question 589: Which of the following has responsibility of data collection for active malaria surveillance at PHC level ?

A. DHO [District Health Officer]
B. MPW [Multipurpose worker] (Correct Answer)
C. MO-PHC [Medical Officer-PHC]
D. DMO [District Medical Officer]

Explanation: ***MPW [Multipurpose Worker]*** - The **Multipurpose Worker (MPW)** is the primary field-level health worker responsible for **active malaria surveillance and data collection** at the PHC level. - MPWs conduct **house-to-house surveys**, identify suspected malaria cases, collect blood smears for testing, maintain surveillance registers, and report data to the MO-PHC. - Under the **National Vector Borne Disease Control Programme (NVBDCP)**, MPWs are specifically designated for active case detection and surveillance activities in their assigned areas. *MO-PHC [Medical Officer-PHC]* - The **Medical Officer-PHC** has **supervisory and administrative responsibility** for malaria control programs at the PHC. - While they oversee surveillance activities, review data, and ensure reporting, they do not perform the actual **field-level data collection** for active surveillance. - The MO-PHC coordinates the program and provides technical guidance to MPWs. *DHO [District Health Officer]* - The **District Health Officer (DHO)** is responsible for health administration at the **district level**, which is a higher administrative tier. - They monitor overall district health outcomes and compile reports from multiple PHCs but are not involved in direct data collection at individual PHCs. *DMO [District Medical Officer]* - The **District Medical Officer (DMO)** is also a senior administrative position at the **district level**. - Their role focuses on district-wide health management, policy implementation, and resource allocation, not direct field-level surveillance data collection.

Question 590: SARS infection case fatality rate of >50% is observed in patients of which age group?

A. < 20 yrs
B. 20 - 40 years
C. 40 - 60 years
D. > 65 years (Correct Answer)

Explanation: ***> 65 years*** - Patients over 65 years old with **SARS** have been observed to have a **case fatality rate exceeding 50%**, indicating a significantly higher risk of severe outcomes and death in this age group. - This increased vulnerability is often attributed to **weakened immune responses** and higher prevalence of **comorbidities** in older adults. *< 20 yrs* - The case fatality rate for SARS in individuals under 20 years old is observed to be **very low**, typically less than 1%. - This age group generally experiences milder symptoms and has a **more robust immune response** compared to older populations. *20 - 40 years* - In the 20-40 year age group, the case fatality rate for SARS is typically **low to moderate**, generally ranging from 1-5%. - While they are at higher risk than younger individuals, their outcomes are significantly better than those in older age groups. *40 - 60 years* - Patients between 40 and 60 years old with SARS have a moderate case fatality rate, usually in the range of **6-15%**. - This age group shows an elevated risk compared to younger adults but does not reach the very high fatality rates seen in the elderly.

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