Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1201: Most common route of infection in pasteurella cellulitis -

A. Animal bites or scratches (Correct Answer)
B. Aerosols or dust
C. Contaminated tissue
D. Human to human

Explanation: ***Animal bites or scratches*** - *Pasteurella multocida* is a common commensal bacterium in the oral flora of **cats and dogs**. - **Animal bites or scratches** are the primary mode of transmission for *Pasteurella* infections, particularly cellulitis, due to direct inoculation. *Aerosols or dust* - Transmission via **aerosols or dust** is rare for *Pasteurella* infections, which typically require direct contact or inoculation. - While other bacteria can spread this way, *Pasteurella* cellulitis is not commonly acquired through airborne routes. *Contaminated tissue* - While possible in some contexts, **contaminated tissue** is not the most common route of infection for *Pasteurella* cellulitis. - Direct inoculation from an **animal's oral flora** is far more frequent than contact with contaminated environmental tissues. *Human to human* - *Pasteurella* infections are generally **not transmissible from human to human**. - The organism is primarily associated with animals and their bites or scratches.

Question 1202: Which of the following statements regarding Pertussis is INCORRECT?

A. The drug of choice is Erythromycin.
B. Cerebellar ataxia is a known complication. (Correct Answer)
C. Some infections may be subclinical.
D. The most infective stage is the catarrhal stage.

Explanation: ***Cerebellar ataxia is a known complication.*** - **Cerebellar ataxia** is not a typical or known complication of pertussis. Complications usually involve the respiratory, neurological (e.g., seizures, encephalopathy due to hypoxia), and nutritional systems due to severe coughing. - While neurological complications can occur, **ataxia** specifically is not frequently sighted in the context of pertussis. *Some infections may be subclinical.* - Some individuals, especially those partially immunized or older, can experience **subclinical or atypical infections** with pertussis, often presenting as a mild cough. - This characteristic makes it difficult to control the spread of the disease as infected individuals may not be recognized. *The most infective stage is the catarrhal stage.* - The **catarrhal stage**, characterized by non-specific cold-like symptoms, is the most contagious phase because bacterial shedding is highest. - During this stage, symptoms are mild and often indistinguishable from a common cold, leading to widespread transmission before diagnosis. *The drug of choice is Erythromycin.* - **Erythromycin**, or other macrolides like azithromycin or clarithromycin, are the drugs of choice for treating pertussis. - These antibiotics are most effective when administered early in the **catarrhal stage** to reduce disease severity and prevent transmission.

Question 1203: Most common complication of diphtheria is -

A. Myocarditis (Correct Answer)
B. Pneumonia
C. Meningitis
D. Endocarditis

Explanation: ***Myocarditis*** - Diphtheria toxin can directly damage myocardial cells, leading to inflammation and dysfunction of the heart muscle, making **myocarditis** the most common and serious complication. - This can result in **heart failure**, arrhythmias, and even death, highlighting its significance in diphtheria. *Pneumonia* - While respiratory complications can occur in diphtheria, **pneumonia** is not the most common or life-threatening complication associated with the diphtheria toxin itself. - Secondary bacterial infections might lead to pneumonia, but it is not a direct toxic effect like myocarditis. *Meningitis* - **Meningitis**, an inflammation of the membranes surrounding the brain and spinal cord, is an extremely rare complication of diphtheria. - Diphtheria primarily affects the upper respiratory tract and heart [1], with neurological complications typically manifesting as neuropathies rather than meningitis. *Endocarditis* - Although diphtheria can cause cardiac complications, **endocarditis** (inflammation of the heart's inner lining, including the valves) is not a common complication. - Myocarditis, due to the direct toxic effect on heart muscle, is far more prevalent than endocarditis in diphtheria.

Question 1204: What is the most common cause of lung abscess in comatose patients?

A. Staph aureus
B. Oral anaerobes (Correct Answer)
C. Klebsiella
D. Tuberculosis

Explanation: Oral anaerobes - **Comatose patients** are at high risk for **aspiration** of oropharyngeal flora, which predominantly consists of anaerobic bacteria. [1] - Aspiration of these organisms, especially in compromised lung tissue, frequently leads to **necrotizing pneumonia** and subsequent abscess formation. [1] *Staph aureus* - While *Staphylococcus aureus* can cause lung abscesses, particularly in the context of **hematogenous spread** (e.g., endocarditis) or nosocomial infections, it is not the most common cause in *comatose patients* who typically aspirate oral flora. [2] - *S. aureus* lung abscesses are often associated with multiple, smaller lesions rather than a single, large abscess from aspiration. *Klebsiella* - *Klebsiella pneumoniae* can cause severe, **rapidly progressive pneumonia** that may lead to abscess formation, especially in individuals with **alcoholism** or **diabetes**. - However, it is less common than oral anaerobes as the primary cause of abscess in the general population of comatose patients, whose main risk factor is aspiration of normal oral flora. [1] *Tuberculosis* - **Mycobacterium tuberculosis** can cause cavitary lung lesions, but these are typically chronic and result from primary or reactivated tuberculosis disease, not acute aspiration. [3] - Lung abscesses caused by tuberculosis are histologically distinct from pyogenic abscesses and are characterized by **granulomatous inflammation** and caseous necrosis.

Question 1205: What is the significance of the absence of Vi-antibody in a patient with typhoid fever?

A. Indicates a poor prognosis
B. Indicates a favorable prognosis (Correct Answer)
C. No impact on prognosis
D. Suggests a negative response to treatment

Explanation: ***Indicates a favorable prognosis*** - The **Vi (Virulence) antigen** is a **polysaccharide capsule** that helps *Salmonella typhi* evade the immune system and is associated with **virulence** and **carrier state development**. - **Absence of Vi-antibody** indicates infection with a **less virulent strain**, successful **immune clearance**, and **lower likelihood** of developing a chronic carrier state. *Indicates a poor prognosis* - The **absence of Vi-antibody** is actually associated with **better outcomes**, not worse prognosis. - **Poor prognosis** in typhoid fever is typically related to complications like **intestinal perforation** or **septic shock**, not Vi-antibody status [1]. *No impact on prognosis* - **Vi-antibody status** is a **recognized prognostic marker** in typhoid fever and does have clinical significance. - The **presence of Vi-antibodies** may indicate **persistent infection** or **carrier state development**, making it a relevant prognostic indicator. *Suggests a negative response to treatment* - **Absence of Vi-antibody** typically indicates **successful treatment response** and **effective clearance** of the organism. - **Negative treatment response** would be evidenced by **persistent fever**, **positive cultures**, or **clinical deterioration** despite appropriate antibiotic therapy.

Question 1206: Which of the following statements about post-exposure prophylaxis (PEP) for HIV is correct?

A. Should be started within 72 hours of exposure (Correct Answer)
B. Should be continued for 4 weeks
C. Standard protocol includes three antiretroviral drugs
D. Involves a combination of antiretroviral drugs for 28 days

Explanation: ***Should be started within 72 hours of exposure*** - PEP is most effective when initiated as soon as possible after a potential HIV exposure, with the **maximum benefit observed within 72 hours**. - Delaying initiation beyond this window significantly **reduces its efficacy** in preventing HIV seroconversion. *Should be continued for 4 weeks* - PEP is typically continued for 28 days, which is approximately **four weeks**. While this statement is generally true, it is not the most crucial initial action. - The duration of 28 days is crucial for ensuring the antiretroviral drugs effectively interrupt the **HIV replication cycle** before it can establish a permanent infection. *Standard protocol includes three antiretroviral drugs* - The standard PEP regimen typically involves a **combination of three antiretroviral drugs**. However, this option alone does not capture the critical timing aspect of PEP. - The combination of three drugs aims to target different stages of the **HIV life cycle** to maximize the chances of preventing infection. *Involves a combination of antiretroviral drugs for 28 days* - This statement accurately describes the components and duration of PEP but does not emphasize the **critical time window** for initiation, which is the most important factor for its effectiveness. - The **28-day duration** with a combination of drugs is designed to cover the period during which initial HIV replication could occur, allowing the drugs to suppress viral activity.

Question 1207: Eschar is seen in all the Rickettsial diseases except:

A. Scrub typhus
B. Rickettsial pox
C. Indian tick typhus
D. Endemic typhus (Correct Answer)

Explanation: ***Endemic typhus*** - **Endemic typhus**, caused by *Rickettsia typhi*, is transmitted by **fleas** and typically presents without an eschar. - The disease is characterized by fever, headache, and a maculopapular rash, but the **inoculation site lesion (eschar) is rare or absent**. *Scrub typhus* - **Scrub typhus**, caused by *Orientia tsutsugamushi*, is known for causing a prominent **eschar** [1] at the site of the **chigger mite bite**. - This **painless black scab** is a classic diagnostic feature of the disease [1]. *Rickettsial pox* - **Rickettsial pox**, caused by *Rickettsia akari*, almost invariably presents with an **eschar**, often referred to as an **inoculation lesion**. - This lesion appears as a papule that vesiculates and then forms a scab, indicating the site of the **mite bite**. *Indian tick typhus* - **Indian tick typhus** (part of the **spotted fever group rickettsioses**), caused by *Rickettsia conorii*, frequently presents with a characteristic **eschar** at the site of the **tick bite**. - This eschar, known as a **tache noire**, is a valuable diagnostic clue in affected patients.

Question 1208: ABO non- secretors are more prone to ?

A. Increased risk of infections (Correct Answer)
B. Autoimmune diseases
C. Cardiovascular diseases
D. Cancer

Explanation: Increased risk of infections - Non-secretors of ABO antigens exhibit an increased susceptibility to a variety of infections, particularly bacterial and viral pathogens. - This is thought to be due to the absence of ABO antigens in secretions, which typically act as decoy receptors to prevent pathogen adhesion to host cells. Autoimmune diseases - While some associations between ABO blood groups and autoimmune diseases exist, non-secretor status is not consistently linked to a higher overall risk of autoimmune conditions. Cardiovascular diseases - ABO blood groups have been associated with cardiovascular risk, with non-O blood types generally having a slightly higher risk of certain cardiovascular events. - However, secretor status (the ability to secrete ABO antigens into bodily fluids) itself is not a prominent independent risk factor for cardiovascular diseases. Cancer - There are some documented associations between specific ABO blood types and certain types of cancer (e.g., non-O blood types with pancreatic cancer), but this is distinct from secretor status. - Being an ABO non-secretor is not a primary, broadly recognized risk factor for developing cancer.

Question 1209: Which of the following statements about gas gangrene is true?

A. Causes mild inflammation of muscles
B. High-dose penicillin is the drug of choice (Correct Answer)
C. Most common cause is Staphylococcus aureus
D. Clostridium perfringens produces heat-sensitive spores

Explanation: ***High-dose penicillin is the drug of choice*** - **High-dose penicillin G** is the primary antibiotic therapy for gas gangrene due to the sensitivity of *Clostridium perfringens* to penicillin. - This aggressive antibiotic treatment is crucial in conjunction with surgical debridement to control the rapidly spreading infection. *Most common cause is Staphylococcus aureus* - The most common cause of gas gangrene is **Clostridium perfringens**, not *Staphylococcus aureus*. - *Staphylococcus aureus* is primarily associated with **pyogenic infections**, cellulitis, and abscesses, not gas gangrene. *Causes mild inflammation of muscles* - Gas gangrene causes **severe myonecrosis** (muscle death) and rapid tissue destruction, not mild inflammation. - The infection leads to necrosis, gas formation in tissues, and systemic toxicity. *Clostridium perfringens produces heat-sensitive spores* - *Clostridium perfringens* produces **heat-resistant spores**, which allow it to survive in harsh conditions and contribute to its pervasive nature in the environment. - The spores are resistant to boiling and can survive for extended periods, making sterilization a challenge.

Question 1210: Which of the following best defines extensively drug-resistant tuberculosis (XDR TB)?

A. MDR TB with resistance to fluoroquinolone, streptomycin, and at least one injectable second-line drug
B. MDR TB with resistance to fluoroquinolone and at least one injectable second-line drug, including Amikacin (Correct Answer)
C. MDR TB with additional resistance to fluoroquinolone and at least one injectable second-line drug
D. MDR TB with resistance to fluoroquinolone and Amikacin, but not to other second-line drugs

Explanation: MDR TB with resistance to fluoroquinolone and at least one injectable second-line drug, including Amikacin - **Extensively drug-resistant TB (XDR TB)** is defined as multidrug-resistant TB (MDR TB) with additional resistance to any **fluoroquinolone** and at least one of the three injectable second-line drugs (Amikacin, Kanamycin, or Capreomycin). - This definition is crucial for guiding treatment regimens, as **XDR TB** is much harder to treat than MDR TB due to fewer effective drug options. MDR TB with resistance to fluoroquinolone, streptomycin, and at least one injectable second-line drug - While resistance to a **fluoroquinolone** and an **injectable second-line drug** is part of the definition, adding **streptomycin** specifically is not necessary for the XDR TB definition alone. - **Streptomycin** is often considered a first-line injectable agent or an older second-line drug, but its specific inclusion beyond "at least one injectable" is not how XDR is formally defined. MDR TB with additional resistance to fluoroquinolone and at least one injectable second-line drug - This option is partially correct but lacks the specificity required for the precise definition of **XDR TB**. - While it correctly mentions resistance to **fluoroquinolones** and an **injectable second-line drug**, it doesn't explicitly state the inclusion of **Amikacin** (or other specific injectables), which is critical for the definition. MDR TB with resistance to fluoroquinolone and Amikacin, but not to other second-line drugs - This definition is too restrictive, as **XDR TB** includes resistance to **fluoroquinolones** and *at least one* of the injectable second-line drugs (Amikacin, Kanamycin, or Capreomycin), not exclusively Amikacin. - The phrase "but not to other second-line drugs" contradicts the broader understanding that resistance to other drugs can still be present, as long as the core XDR criteria are met.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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