Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 701: Chemoprophylaxis is not indicated in which of the following?

A. Meningococcemia
B. Cholera
C. Measles (Correct Answer)
D. Plague

Explanation: ***Measles*** - **Chemoprophylaxis is not routinely indicated for measles** as it is a viral disease primarily prevented by vaccination. - Post-exposure prophylaxis for measles typically involves **measles vaccine** or **immunoglobulin** for susceptible contacts, not antibiotics or antivirals. *Cholera* - **Chemoprophylaxis with antibiotics** (e.g., doxycycline, azithromycin) can be indicated for close contacts of confirmed cholera cases, especially in outbreaks or high-risk settings, to prevent further spread. - This is due to cholera being a bacterial infection that can rapidly transmit through contaminated water and food. *Meningococcemia* - **Chemoprophylaxis is strongly recommended** for close contacts of individuals with invasive meningococcal disease (meningococcemia or meningococcal meningitis) to prevent secondary cases. - Oral **rifampin, ciprofloxacin, or ceftriaxone** are commonly used for this purpose to eliminate carriage of *Neisseria meningitidis*. *Plague* - **Chemoprophylaxis with antibiotics** (e.g., doxycycline, ciprofloxacin) is indicated for individuals with high-risk exposure to plague, such as close contact with an infected person or animal, or laboratory exposure. - This is a serious bacterial infection caused by *Yersinia pestis* where early intervention can prevent severe disease and death.

Question 702: Which of the following represents the WHO recommended message/theme for HIV testing?

A. Unite for Everyone
B. HIV Awareness for All
C. Health for Everyone
D. Everyone counts (Correct Answer)

Explanation: ***Everyone counts*** - "Everyone counts" is the current **WHO recommended message for HIV testing**, emphasizing that reaching all individuals with HIV testing services is crucial to ending the HIV epidemic. - This theme highlights the importance of **equity and access** to testing for all populations, including marginalized and hard-to-reach groups. *Unite for Everyone* - This phrase is not the official slogan or recommendation for **HIV testing** from the WHO. - While promoting unity is important in public health, it does not specifically encapsulate the current **WHO strategy** for HIV testing. *HIV Awareness for All* - This is a general statement about **public health education** but does not represent the specific **WHO recommendation** for HIV testing strategy. - While **awareness** is a component of public health, the current WHO recommendation focuses on a more direct call to action regarding testing. *Health for Everyone* - This is a broad public health message and not the specific **WHO recommendation for HIV testing**. - It represents a general goal of global health efforts rather than a targeted message for **HIV testing initiatives**.

Question 703: Which of the following statements is true regarding the epidemiology of influenza?

A. Pandemics cannot occur with influenza viruses.
B. Incubation period is typically 7-10 days.
C. Humans are the only reservoir for influenza.
D. Asymptomatic cases can occur and may contribute to transmission. (Correct Answer)

Explanation: ***Asymptomatic cases can occur and may contribute to transmission.*** - Asymptomatic or mildly symptomatic individuals can shed the virus, contributing to the silent spread of influenza within a community. - This characteristic makes **influenza control** challenging, as not all infected individuals seek medical attention or are easily identified. *Incubation period is typically 7-10 days.* - The typical incubation period for influenza is much shorter, usually **1 to 4 days**, with an average of 2 days. - A 7-10 day incubation period is more characteristic of infections like **measles** or **mumps**, not influenza. *Pandemics cannot occur with influenza viruses.* - Influenza viruses are well-known for their potential to cause **pandemics** through antigenic shifts, leading to novel strains against which the population has little to no immunity. - Historically, there have been several major influenza pandemics, such as the **1918 Spanish Flu** and the 2009 H1N1 pandemic. *Humans are the only reservoir for influenza.* - While humans are a significant reservoir, influenza viruses also circulate in **animal reservoirs** such as birds (especially wild aquatic birds) and pigs. - These animal reservoirs can serve as sources for new human strains through **inter-species transmission** and genetic reassortment.

Question 704: In which of the following conditions is mass prophylaxis typically recommended during outbreaks?

A. Vitamin A deficiency outbreak
B. Scabies outbreak (Correct Answer)
C. Worm infestation outbreak
D. Lymphatic filariasis outbreak

Explanation: ***Scabies outbreak*** - **Mass treatment** of all exposed individuals is the standard outbreak response for scabies, especially in institutional settings like nursing homes, schools, hostels, or military barracks. - This involves **simultaneous treatment** of both symptomatic cases and asymptomatic contacts to break the transmission cycle during an active outbreak. - This is the only option that requires an immediate, coordinated mass intervention specifically in response to an outbreak situation. *Vitamin A deficiency outbreak* - Vitamin A supplementation is a **nutritional intervention** for endemic deficiency, not an infectious disease requiring mass prophylaxis. - While important for child health programs, it does not address pathogen transmission or outbreak control. *Worm infestation outbreak* - Mass deworming programs exist but are typically **routine, periodic interventions** in endemic areas rather than emergency outbreak responses. - These are scheduled control programs (e.g., biannual school-based deworming) not triggered by acute outbreaks. - They are part of long-term helminth control strategies, not rapid outbreak management. *Lymphatic filariasis outbreak* - **Mass drug administration (MDA)** for filariasis is a multi-year **elimination strategy** in endemic regions, not an outbreak response. - Lymphatic filariasis does not present as acute outbreaks requiring immediate mass prophylaxis. - MDA campaigns are planned, systematic interventions targeting entire endemic populations over 5-6 years.

Question 705: Which of the following statements about Q fever is true?

A. The mode of transmission is by inhalation of contaminated aerosols. (Correct Answer)
B. It commonly presents with a characteristic rash and local lesion at the site of inoculation.
C. Ticks are the primary vector for human transmission.
D. It is primarily a disease of humans with occasional animal involvement.

Explanation: ***The mode of transmission is by inhalation of contaminated aerosols.*** - Q fever is primarily transmitted to humans through the inhalation of **aerosols contaminated with Coxiella burnetii**, originating from infected livestock such as cattle, sheep, and goats. - The bacteria are found in high concentrations in **birth products (placenta, amniotic fluid) of infected animals**, which become aerosolized and readily inhaled. - This is the **most common and significant route** of human infection. *It commonly presents with a characteristic rash and local lesion at the site of inoculation.* - This is **incorrect**. Q fever typically does NOT present with a rash or local lesion. - The disease is acquired by **inhalation**, not through skin inoculation, so there is no entry site lesion. - While rare maculopapular rashes may occur in some cases, they are **not characteristic features** of Q fever. *It is primarily a disease of humans with occasional animal involvement.* - This is **incorrect**. Q fever is a **zoonotic disease** primarily affecting animals. - Humans are **accidental hosts** who acquire infection from infected livestock. - The primary reservoirs are **cattle, sheep, and goats**, with humans representing spillover infections. *Ticks are the primary vector for human transmission.* - This is **incorrect**. While ticks can harbor *Coxiella burnetii* and may play a role in animal-to-animal transmission, they are **not the primary vector for human infection**. - Human transmission occurs predominantly through **aerosol inhalation**, not arthropod bites. - Ticks are considered a **minor or negligible route** of transmission to humans.

Question 706: The infectivity of chickenpox lasts for which of the following?

A. Until all lesions have crusted over (Correct Answer)
B. Till the fever subsides
C. Until the last scab falls off
D. 3 days after the onset of rash

Explanation: ***Correct: Until all lesions have crusted over*** - The period of **infectivity** for chickenpox (varicella-zoster virus) extends from **1-2 days before the rash appears** until **all lesions have completely crusted over**. - This is the **standard clinical endpoint** recommended by CDC, WHO, and public health guidelines for determining when a patient is no longer infectious. - Crusting typically occurs **5-7 days after rash onset**, but the endpoint is clinical (complete crusting) rather than a fixed number of days. - Once all lesions are crusted, viral shedding has effectively ceased and transmission risk is negligible. *Incorrect: Until the last scab falls off* - This is **overly cautious** and unnecessarily prolongs isolation beyond the infectious period. - Infectivity ends when lesions **crust over**, not when the dried scabs eventually fall off during the healing phase. - The scab-falling phase can take weeks and represents skin healing, not active infection. *Incorrect: 3 days after the onset of rash* - This period is **too short** as most lesions are still in the vesicular or pustular stage at 3 days. - Patients remain **highly contagious** at this stage with active viral shedding. - Releasing from isolation at this point would significantly increase transmission risk. *Incorrect: Till the fever subsides* - **Fever** typically resolves within 3-5 days, often before all skin lesions have crusted. - Patients remain **infectious** even after fever resolution if vesicular lesions are still present. - Using fever as the endpoint would result in premature release from isolation and ongoing transmission risk.

Question 707: According to standard guidelines, post-exposure prophylaxis is routinely recommended after ANY potential exposure for which of the following infections?

A. HBV
B. Diphtheria
C. Measles
D. Rabies (Correct Answer)

Explanation: ***Rabies*** - **Rabies post-exposure prophylaxis (PEP) is ALWAYS recommended** after any potential exposure (Category II/III wounds) **regardless of vaccination status** due to the near 100% fatality rate once symptoms appear. - PEP is initiated immediately and involves **wound care**, administration of **rabies immune globulin (RIG)** for previously unvaccinated individuals, and a series of **rabies vaccines**. - Unlike other infections, there is **no screening or assessment of immune status required** - exposure alone mandates PEP. *HBV* - Hepatitis B post-exposure prophylaxis is **conditional** - recommended only for unvaccinated individuals or those with unknown vaccination status after significant exposure. - Those with documented immunity (anti-HBs >10 mIU/mL) do **not require PEP**. - Not routine for all exposures. *Diphtheria* - Diphtheria post-exposure prophylaxis is recommended **only for close contacts** of confirmed cases, particularly if unvaccinated or uncertain vaccination history. - Fully vaccinated individuals with recent boosters may not require prophylaxis. - Not routine for all potential exposures. *Measles* - Measles post-exposure prophylaxis is recommended **only for susceptible individuals** (unvaccinated or no evidence of immunity). - Those with documented immunity do not require PEP. - Requires assessment of immune status before administration.

Question 708: The best way to prevent MRSA outbreak in indoor patients is:

A. Practice proper meticulous hand washing (Correct Answer)
B. Administer vancomycin to all patients
C. Conduct fumigation of the ward
D. Use sodium hypochlorite for floor disinfection

Explanation: ***Practice proper meticulous hand washing*** - **Hand hygiene** is the most effective measure to prevent the transmission of **healthcare-associated infections**, including Methicillin-resistant *Staphylococcus aureus* (**MRSA**). - Consistent **hand washing** by healthcare workers removes transient microorganisms and significantly reduces cross-contamination between patients. *Administer vancomycin to all patients* - Administering **vancomycin** to all patients would lead to widespread **antibiotic resistance**, making infections harder to treat. - This practice is inappropriate as **vancomycin** is a broad-spectrum antibiotic and should be reserved for confirmed infections or specific prophylaxis. *Conduct fumigation of the ward* - **Fumigation** is generally not recommended for routine MRSA prevention as it has limited efficacy against bacterial spores and poses risks to staff and patients. - It is an extreme measure reserved for specific, highly contaminated environments and does not address the primary mode of MRSA transmission (person-to-person). *Use sodium hypochlorite for floor disinfection* - While **sodium hypochlorite** is an effective disinfectant, focusing solely on floor disinfection is insufficient for preventing **MRSA outbreaks**. - MRSA primarily spreads through direct contact via contaminated hands, rather than contact with contaminated floors.

Question 709: All of the following are related to plague, except which of the following?

A. Burrow index
B. Aedes aegypti index (Correct Answer)
C. Cheopis index
D. Total flea index

Explanation: ***Aedes aegypti index*** - The **Aedes aegypti index** measures the prevalence of *Aedes aegypti* mosquitoes, which are vectors for diseases like **dengue**, **Zika**, **chikungunya**, and **yellow fever**. - Plague is primarily transmitted by fleas, not mosquitoes. *Total flea index* - The **total flea index** quantifies the average number of fleas per rodent, which is a direct measure of potential plague transmission risk from rodent to human populations. - A higher total flea index indicates a greater likelihood of plague outbreaks. *Burrow index* - The **burrow index** measures the number of active rodent burrows per unit area, indicating rodent population density. - Plague is maintained in **rodent populations**, and a high burrow index can suggest a sustained risk for enzootic plague. *Cheopis index* - The **Cheopis index** (or Xenopsylla cheopis index) specifically measures the average number of *Xenopsylla cheopis* (oriental rat flea) per rodent found. - *Xenopsylla cheopis* is the **primary vector** for plague transmission, making this index a critical indicator for monitoring plague risk.

Question 710: Which bacterial disease is commonly associated with the three "Rs": rats, rice fields, and rainfall?

A. Leptospirosis (Correct Answer)
B. Bubonic plague
C. Haverhill fever
D. Melioidosis

Explanation: ***Leptospirosis*** - This disease is directly associated with exposure to environments contaminated by **animal urine**, often linked to **rats** in environments like **rice fields** where **rainfall** creates favorable conditions for bacterial survival and transmission. - The classic **"3 Rs" mnemonic** (Rats, Rice fields, Rainfall) specifically describes leptospirosis epidemiology. - **Leptospira** bacteria typically enter the body through cuts or abrasions in the skin or through mucous membranes, especially when prolonged exposure to contaminated water occurs. - Common in **occupational groups**: farmers, sewer workers, veterinarians, and military personnel. *Bubonic plague* - Characterized by acute onset of fever, chills, weakness, and painful, swollen lymph nodes called **buboes**, caused by **Yersinia pestis**. - Primarily transmitted to humans through bites of **infected fleas** that have fed on rodents, not directly through contaminated water or rice fields. - While associated with rats, lacks the rice field and rainfall environmental components. *Haverhill fever* - Caused by **Streptobacillus moniliformis**, a form of **rat-bite fever** contracted through rodent contact or ingestion of contaminated food/water. - While associated with rats, it doesn't have the specific environmental triad of **rice fields** and **rainfall** as central to its epidemiology like leptospirosis. - Transmission is primarily through rat bites or contaminated milk products. *Melioidosis* - Caused by **Burkholderia pseudomallei**, found in soil and water in tropical and subtropical regions. - While found in water and soil with potential agricultural exposure, it is **not specifically linked** to the "rats, rice fields, and rainfall" triad that defines leptospirosis. - More commonly associated with direct soil contact rather than rat-contaminated environments.

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