Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1031: Which of the following is true about polio?

A. Paralytic polio is most common
B. Causes spastic paralysis
C. Polio drops given only to children under 3
D. Risk of paralysis increases with tonsillectomy (Correct Answer)

Explanation: ***Risk of paralysis increases with tonsillectomy*** - Tonsillectomy, especially when performed during an active poliovirus infection, has been linked to an **increased risk** of paralytic polio, particularly **bulbar polio**. - The surgical trauma may facilitate viral spread to the **central nervous system** [1] or alter immune responses, making the individual more susceptible to severe disease. *Paralytic polio is most common* - The vast majority of poliovirus infections are **asymptomatic** or cause **mild, non-specific symptoms**. - Only a small percentage of infected individuals (about 1 in 200) develop **paralytic polio**. *Causes spastic paralysis* - Poliovirus primarily affects **anterior horn cells** in the spinal cord, causing **flaccid paralysis** due to damage to lower motor neurons. - **Spastic paralysis** results from upper motor neuron damage, which is not characteristic of polio. *Polio drops given only to children under 3* - Oral polio vaccine (OPV, or "polio drops") is typically given to children in multiple doses from **birth** up to **5 years of age** in endemic regions. - The exact schedule varies by country, but it extends beyond just children under 3 to ensure comprehensive immunity.

Question 1032: All are features of septic arthritis except:

A. Joint swelling
B. Symmetric joint involvement (Correct Answer)
C. Painful joint movement
D. Elevated ESR

Explanation: Symmetric joint involvement - Septic arthritis typically presents as a monoarticular condition [1], affecting a single joint, or sometimes a few joints in an asymmetric pattern. - Symmetrical joint involvement is more characteristic of inflammatory arthropathies like rheumatoid arthritis, not septic arthritis [1]. Joint swelling - Inflammation and the accumulation of effusion in the joint capsule due to infection commonly lead to noticeable joint swelling. - This is a hallmark symptom as the body responds to bacterial invasion within the joint space. Painful joint movement - The acute inflammatory process and distension of the joint capsule by infection cause significant pain with any movement or weight-bearing. - Patients often present with an unwillingness to move the affected joint, characteristic of a "pseudoparalysis". Elevated ESR - Erythrocyte sedimentation rate (ESR) is a general marker of inflammation and is typically significantly elevated in septic arthritis due to the systemic inflammatory response to infection. - This indicator helps confirm the presence of an active inflammatory process, though it is not specific to septic arthritis.

Question 1033: A 50-year-old farmer presents with cough, fever, and weight loss. CXR shows upper lobe cavitary lesions. Sputum culture reveals acid-fast bacilli resistant to isoniazid and rifampin. What is the next best drug?

A. Linezolid
B. Fluoroquinolone (Correct Answer)
C. Ethambutol
D. Pyrazinamide

Explanation: **Fluoroquinolone** - In cases of **multidrug-resistant tuberculosis (MDR-TB)**, which is defined by specific resistance to both **isoniazid** and **rifampin**, fluoroquinolones are a crucial second-line agent [1]. - They demonstrate excellent **mycobactericidal activity** and are a cornerstone of MDR-TB treatment regimens [1]. *Linezolid* - While **Linezolid** is used in highly resistant TB cases (XDR-TB), it is generally reserved for situations where other core second-line drugs (like fluoroquinolones) cannot be used or are resistant. - Its use often carries a higher risk of **myelosuppression** and **neuropathy**, making it less preferred as an initial choice for MDR-TB. *Ethambutol* - **Ethambutol** is a first-line antitubercular drug, but it is typically used in conjunction with isoniazid and rifampin to prevent resistance development [1]. - It would not be the "next best" drug when **TB is already resistant to isoniazid and rifampin**, as single-drug therapy is ineffective for MDR-TB and could lead to further resistance. *Pyrazinamide* - **Pyrazinamide** is another first-line drug primarily effective against semi-dormant bacilli in acidic environments [1]. - Similar to ethambutol, it is not appropriate as the "next best" drug to manage **MDR-TB** when resistance to standard first-line agents has already been identified.

Question 1034: A 45-year-old male presents with fever, cough, and cavitary lesion on CXR. What is the most likely diagnosis?

A. Sarcoidosis
B. TB (Correct Answer)
C. Lung cancer
D. Lung abscess

Explanation: ***TB*** - **Cavitary lesions** on CXR, accompanied by **fever and cough**, are highly suggestive of **pulmonary tuberculosis**, particularly in endemic areas or with risk factors [1]. - **Mycobacterium tuberculosis** leads to granuloma formation, which can undergo caseous necrosis and cavitation [2]. *Sarcoidosis* - Characterized by **non-caseating granulomas** and typically presents with **bilateral hilar lymphadenopathy** and interstitial lung disease, less commonly with cavitary lesions. - While it can cause cough and fever, cavitary lesions are not its hallmark presentation. *Lung cancer* - Can present with cough and a lung mass, which may sometimes cavitate, but fever is not a primary symptom unless there is an associated infection or paraneoplastic syndrome. - A persistent **cavitary lesion** without other typical features of malignancy makes **TB** a more probable diagnosis, especially given the fever. *Lung abscess* - A **lung abscess** is a necrotic infection of the lung parenchyma, resulting in a cavity filled with pus, often caused by aspiration. - While it typically presents with fever and cough and can show a cavitary lesion on CXR, the question doesn't provide context for aspiration or an acute bacterial infection. **TB** is a more systemic and chronic disease with these findings.

Question 1035: A 45-year-old HIV-positive man presents with fever and cough. Sputum culture shows acid-fast bacilli. Which of the following drugs is essential in the treatment regimen?

A. Doxycycline
B. Amoxicillin
C. Isoniazid (Correct Answer)
D. Ciprofloxacin

Explanation: ***Isoniazid*** - The presence of **acid-fast bacilli** (AFB) in sputum, especially in an **HIV-positive** individual with fever and cough, strongly indicates **tuberculosis (TB)** [1]. - **Isoniazid** is a cornerstone drug in **first-line anti-tuberculosis therapy** and is essential for effective treatment [1]. *Doxycycline* - **Doxycycline** is a tetracycline antibiotic primarily used for bacterial infections like **atypical pneumonia**, Lyme disease, and certain sexually transmitted infections. - It has **no significant activity against Mycobacterium tuberculosis** and is not part of TB treatment. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic effective against a range of common bacterial infections, but it is **ineffective against mycobacteria**. - It would not be used to treat **tuberculosis**. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic used for various bacterial infections, including some respiratory and urinary tract infections. - While some fluoroquinolones are used as **second-line agents** in specific multi-drug resistant TB regimens, **ciprofloxacin** is not a first-line drug and is generally reserved for particular circumstances, unlike isoniazid which is essential for initial therapy.

Question 1036: A healthcare worker develops fever, night sweats, and cough. Sputum shows acid-fast bacilli. What is the next diagnostic test?

A. Gram stain
B. Serology for TB
C. NAAT for TB (Correct Answer)
D. Sputum culture

Explanation: ***NAAT for TB*** - Nucleic Acid Amplification Tests (**NAAT**) rapidly confirm the presence of **Mycobacterium tuberculosis** DNA or RNA, crucial after an **acid-fast bacilli (AFB) smear** is positive [1]. - This test offers high sensitivity and specificity and can also detect **drug resistance**, guiding immediate treatment decisions [1]. *Gram stain* - A **Gram stain** is not appropriate for **Mycobacterium tuberculosis** because these bacteria have a unique cell wall that makes them **acid-fast**, not readily stained by the Gram method. - The initial finding of **acid-fast bacilli** already indicates a general type of organism, making a Gram stain redundant and uninformative for TB. *Serology for TB* - **Serological tests for TB** (detecting antibodies to M. tuberculosis) are generally **not recommended** for the diagnosis of active pulmonary TB due to their **poor sensitivity and specificity**. - They have limited utility in diagnosing active disease and are not endorsed by major health organizations for this purpose. *Sputum culture* - **Sputum culture** is the **gold standard** for confirming TB diagnosis and for **drug susceptibility testing**, but it is a **slow process** (taking several weeks) [2]. - While essential for definitive diagnosis and resistance profiling, it is not the **"next" rapid diagnostic test** required given the positive AFB smear.

Question 1037: A patient presents with fever and retro-orbital pain. Which investigation should be conducted next for confirmation of dengue fever?

A. Viral culture
B. NS1 antigen test (Correct Answer)
C. IgM ELISA
D. PCR

Explanation: ***NS1 antigen test*** - The **NS1 antigen test** is highly sensitive and specific for dengue in the **early stages** of infection (typically 0-7 days after symptom onset), which is when a patient with fever and retro-orbital pain would likely present. - It detects a non-structural protein of the dengue virus, indicating **active viral replication**. *Viral culture* - **Viral culture** for dengue is time-consuming and technically demanding, making it impractical for rapid diagnosis in clinical settings, especially when an urgent confirmation is needed for patient management. - It is primarily used for research purposes rather than routine clinical diagnosis [2]. *IgM ELISA* - **IgM ELISA** detects antibodies produced in response to dengue infection, which typically become detectable **5-7 days after symptom onset**. - While useful for confirming dengue in later stages of illness, it may yield a **false negative** result if performed too early in the course of the disease [2]. *PCR* - **PCR (Polymerase Chain Reaction)** detects dengue viral RNA and is highly sensitive and specific in the **early acute phase** of infection (first 5 days) [1]. - However, it is generally more expensive, requires specialized laboratory equipment, and has a longer turnaround time compared to the NS1 antigen test, making NS1 a more accessible initial diagnostic choice.

Question 1038: A 40-year-old patient presents with frequent watery diarrhea after a recent course of antibiotics. Stool toxin assay is positive for Clostridium difficile. What is the most appropriate treatment?

A. IV metronidazole
B. Oral vancomycin (Correct Answer)
C. IV ciprofloxacin
D. Oral doxycycline

Explanation: ***Oral vancomycin*** - **Oral vancomycin** is the **first-line treatment** for *Clostridium difficile* infection (CDI) due to its high efficacy against *C. difficile* and its inability to be absorbed systemically, allowing high concentrations to remain in the gut lumen [1]. - It directly targets the bacteria in the gastrointestinal tract, making it superior to IV antibiotics for localized gut infections. *IV metronidazole* - While **IV metronidazole** was previously used for severe CDI, its efficacy is inferior to oral vancomycin, especially in severe cases, because it does not achieve high enough luminal concentrations. - It is often reserved for circumstances where oral administration is not possible or in combination with oral vancomycin for critically ill patients. *IV ciprofloxacin* - **IV ciprofloxacin** is a fluoroquinolone antibiotic and is **not effective** against *C. difficile*; in fact, fluoroquinolones are a common risk factor for developing CDI [1]. - Using ciprofloxacin would exacerbate the infection rather than treat it. *Oral doxycycline* - **Oral doxycycline** is a tetracycline antibiotic and has **no established efficacy** against *Clostridium difficile* infection. - It would not be an appropriate treatment and could potentially worsen the patient's condition by disrupting the gut microbiome further.

Question 1039: A patient presents with hemoptysis, weight loss, and fatigue. Chest X-ray shows cavitary lesions in the upper lobes. What is the most likely diagnosis?

A. Lung abscess
B. Pulmonary embolism
C. Bronchiectasis
D. Tuberculosis (Correct Answer)

Explanation: ### Tuberculosis - The combination of **hemoptysis**, **weight loss**, and **fatigue** is highly suggestive of active pulmonary tuberculosis [1, 2]. - **Cavitary lesions** in the **upper lobes** on chest X-ray are a classic radiographic finding for post-primary (reactivation) tuberculosis [3]. ### Lung abscess - While it can cause **hemoptysis** and **fatigue**, weight loss is less prominent unless chronic, and abscesses are typically solitary and may be located anywhere in the lung, not exclusively upper lobes [1]. - Lung abscesses are often associated with **fever**, **purulent sputum**, and a history of **aspiration**, which are not mentioned. ### Pulmonary embolism - Symptoms usually include **acute dyspnea**, **chest pain**, and sometimes **hemoptysis**, but **weight loss** and **fatigue** are not typical chronic symptoms [1]. - Chest X-rays in pulmonary embolism usually show **normal findings** or **non-specific changes** like a Westermark sign or Hampton hump, not cavitations. ### Bronchiectasis - Characterized by **chronic cough with copious purulent sputum** and recurrent infections, leading to **dilated bronchi**. - While **hemoptysis** can occur due to bronchial artery erosion, **weight loss** is less common, and chest X-rays typically show **"tram-track" opacities** or **cystic changes**, not cavitations as the primary finding [1].

Question 1040: Which pathogen is most commonly associated with a productive cough in chronic bronchitis?

A. Legionella pneumophila
B. Streptococcus pneumoniae
C. Haemophilus influenzae (Correct Answer)
D. Mycoplasma pneumoniae

Explanation: ***Haemophilus influenzae*** - This bacterium is a common cause of exacerbations in patients with **chronic bronchitis**, leading to increased sputum production and cough. - It frequently colonizes the airways of individuals with pre-existing lung disease, including **COPD**, making them susceptible to infection. [2] *Legionella pneumophila* - This pathogen typically causes **Legionnaires' disease**, a severe form of pneumonia, often presenting with systemic symptoms and atypical features rather than a straightforward exacerbation of chronic bronchitis. [1] - Infection is usually linked to exposure to contaminated water sources, and while it causes cough, it's not the most common cause of a productive cough in established chronic bronchitis. [2] *Streptococcus pneumoniae* - While *Streptococcus pneumoniae* is a common cause of **community-acquired pneumonia** and can infect individuals with chronic bronchitis, *Haemophilus influenzae* is more frequently isolated in exacerbations presenting predominantly with a productive cough. [1] - *S. pneumoniae* infections often present with more severe symptoms, including high fever and lobar consolidation. *Mycoplasma pneumoniae* - This pathogen is known for causing **"walking pneumonia"**, which typically presents with a persistent, non-productive cough, along with headache and malaise. - It is not commonly associated with the copious, productive cough characteristic of an acute exacerbation of chronic bronchitis.

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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