Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1241: Which of the following is NOT a common pathogen causing pneumonia in COPD patients?

A. Klebsiella pneumoniae
B. Legionella spp (Correct Answer)
C. Pseudomonas aeruginosa
D. Haemophilus influenzae

Explanation: ***Legionella spp*** - While *Legionella* can cause pneumonia, it is **not a common pathogen** specifically in COPD exacerbations or community-acquired pneumonia in these patients [1]. - *Legionella* pneumonia often presents with **extrapulmonary symptoms** like diarrhea and hyponatremia and is typically associated with contaminated water sources [1]. *Haemophilus influenzae* - This is a very common pathogen causing both **acute exacerbations of COPD (AECOPD)** and pneumonia in patients with underlying COPD [1]. - COPD patients often have **impaired mucociliary clearance** and altered airway microbiology, making them susceptible to *H. influenzae* colonization and infection [1]. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is an important pathogen in **severe COPD exacerbations**, especially in patients with frequent exacerbations, bronchiectasis, or prior antibiotic use. - Its presence often indicates a **more severe disease course** and requires specific antibiotic coverage. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* is a significant cause of **pneumonia in immunocompromised individuals**, including those with COPD, diabetes, or alcoholism. - It often leads to **severe, necrotizing pneumonia**, particularly in the upper lobes, and can cause abscess formation.

Question 1242: Which type of malaria is most commonly associated with renal failure?

A. Falciparum (Correct Answer)
B. Vivax
C. Malariae
D. Ovale

Explanation: ***Falciparum*** - **Plasmodium falciparum** is notorious for its ability to cause severe and complicated malaria, including **renal failure** due to its high parasitic biomass and tendency to block microvasculature [1]. - The parasite causes red blood cells to become **sticky**, leading to sequestration in capillaries of vital organs, including the kidneys, resulting in acute tubular necrosis [1]. *Vivax* - **Plasmodium vivax** typically causes milder forms of malaria, though it can occasionally lead to severe manifestations, **renal complications are rare** compared to P. falciparum [1]. - While it can cause some organ dysfunction, it generally does not cause the severe multi-organ involvement, particularly **acute renal failure**, that P. falciparum is known for [1]. *Malariae* - **Plasmodium malariae** is associated with a chronic form of malaria and is known to cause **nephrotic syndrome** (specifically malarial nephropathy) due to immune complex deposition, rather than acute renal failure [1]. - The renal pathology in P. malariae infection is typically a **glomerulonephritis** that develops after repeated infections, which is distinct from the acute renal failure seen with P. falciparum [1]. *Ovale* - **Plasmodium ovale** is the least common type of malaria and causes a benign form of the disease, similar to P. vivax [1]. - It rarely, if ever, causes severe complications like **renal failure** [1].

Question 1243: Meningitis with rash is seen in -

A. Neisseria meningitidis (Correct Answer)
B. H. influenzae
C. Strepto. agalactae
D. Pneumococcus

Explanation: **Neisseria meningitidis** - **Meningococcal meningitis** is classically associated with an acute onset of fever, headache, stiff neck, and a characteristic **petechial or purpuric rash** [1]. - The rash is due to widespread **vasculitis** and disseminated intravascular coagulation (DIC) caused by the bacteria. *H. influenzae* - While *H. influenzae* type b (Hib) was a major cause of bacterial meningitis before vaccination, it typically does not cause a *rash*. - Meningitis caused by *H. influenzae* presents with fever, headache, stiff neck, and altered mental status without dermatological manifestations. *Strepto. agalactiae* - *Streptococcus agalactiae* (Group B Strep) is a common cause of meningitis in **neonates** and infants. - It usually presents with non-specific symptoms like fever, lethargy, and poor feeding, and a rash is not a typical feature of GBS meningitis. *Pneumococcus* - *Streptococcus pneumoniae* (Pneumococcus) is another leading cause of bacterial meningitis in adults and children [1]. - Symptoms include fever, headache, stiff neck, and altered mental status, but a cutaneous rash is not characteristic of pneumococcal meningitis [1].

Question 1244: Tabes dorsalis is seen in -

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

Explanation: ***Tertiary syphilis*** - **Tabes dorsalis** is a neurological manifestation of **tertiary syphilis**, characterized by demyelination and degeneration of the posterior columns of the spinal cord [1]. - This leads to symptoms such as **ataxia**, **loss of proprioception**, **lightning pains**, and **Argyll-Robertson pupils**. *Primary syphilis* - Characterized by the presence of a **chancre**, a painless ulcer, at the site of infection [1]. - This stage typically occurs 3-90 days after exposure and is not associated with neurological complications of tabes dorsalis. *Latent syphilis* - This is a period during which there are **no clinical signs or symptoms** of syphilis, although the infection persists. - It can be early or late, but it is not the stage where overt neurological complications like tabes dorsalis arise [1]. *Secondary syphilis* - This stage typically presents with a **generalized mucocutaneous rash**, **lymphadenopathy**, and **condylomata lata** [1]. - While it can involve various organ systems, it does not typically include the severe neurological degeneration seen in tabes dorsalis.

Question 1245: Serological testing of patient shows HBsAg, IgM anti-HBc and HBeAg positive. The patient has -

A. Acute hepatitis B with high infectivity (Correct Answer)
B. Chronic hepatitis with high infectivity
C. Acute on chronic hepatitis
D. Chronic hepatitis B with low infectivity (not acute)

Explanation: ***Acute hepatitis B with high infectivity*** - The presence of **HBsAg** (hepatitis B surface antigen) indicates active infection, while **IgM anti-HBc** (IgM antibody to hepatitis B core antigen) is a marker of recent or acute infection [1]. - **HBeAg** (hepatitis B e-antigen) positivity signifies active viral replication and a high likelihood of infectivity [1]. *Chronic hepatitis B with low infectivity (not acute)* - **Chronic hepatitis B** is characterized by the presence of **HBsAg for more than six months**, but **IgM anti-HBc** would typically be negative; instead, **IgG anti-HBc** would be positive [1]. - **Low infectivity** would be indicated by the absence of **HBeAg**, replaced by **anti-HBe** (antibody to HBeAg) [1]. *Chronic hepatitis with high infectivity* - This diagnosis would show positive **HBsAg and HBeAg**, but the absence of **IgM anti-HBc** (presence of **IgG anti-HBc** instead) would distinguish it from acute infection [1]. - The presence of **IgM anti-HBc** is a crucial marker for an acute phase of hepatitis B rather than chronic. *Acute on chronic hepatitis* - This scenario would involve a patient with pre-existing **chronic hepatitis B** (positive HBsAg, IgG anti-HBc) experiencing a new acute flare-up, which could involve a resurgence of **HBeAg** or a new acute viral insult. - While **HBsAg** and **HBeAg** would be positive, the key differentiator would be the presence of both **IgM anti-HBc** (indicating the acute component) and **IgG anti-HBc** (indicating the chronic component), which is not fully described here to confirm acute on chronic.

Question 1246: Which species of malaria is associated with nephrotic syndrome?

A. P. vivax
B. P. falciparum
C. P. malariae (Correct Answer)
D. P. ovale

Explanation: ***P. malariae*** - *P. malariae* infection is classically associated with **quartan fever** and can lead to **nephrotic syndrome**, particularly in children [1]. - The mechanism involves the deposition of immune complexes in the glomeruli, causing **membranoproliferative glomerulonephritis**. *P. vivax* - *P. vivax* is known for causing **benign tertian malaria** and frequently leads to **relapses** due to hypnozoites in the liver [1]. - While it can cause renal dysfunction, **nephrotic syndrome** is not a characteristic complication. *P. falciparum* - *P. falciparum* is responsible for the most severe form of malaria, often complicated by **cerebral malaria**, **acute renal failure**, and **blackwater fever** [1]. - Renal complications typically present as **acute tubular necrosis** rather than nephrotic syndrome. *P. ovale* - *P. ovale* causes **mild tertian malaria** similar to *P. vivax* and is also known for **relapses** due to hypnozoites [1]. - It is the least common form of malaria and is not typically associated with **nephrotic syndrome**.

Question 1247: HIV post exposure prophylaxis should be started within?

A. 1-2 hrs
B. 14 hrs
C. 18 hrs
D. 72 hrs (Correct Answer)

Explanation: ***72 hrs*** - **Post-exposure prophylaxis (PEP)** aims to prevent HIV infection after potential exposure and should ideally be initiated as soon as possible, but no later than **72 hours** after exposure [1]. - Starting PEP within this window significantly increases its effectiveness in preventing HIV seroconversion. *1-2 hrs* - While initiating PEP as soon as possible is crucial, stating it must be within **1-2 hours** can be misleading as the window of effectiveness extends beyond this. - This timeframe might be an ideal, but not the absolute crucial limit for efficacy. *14 hrs* - This timeframe is **too restrictive** for the recommended window for PEP initiation. - Missing the opportunity within **14 hours** does not negate the effectiveness of PEP if started within the broader 72-hour window. *18 hrs* - Similar to **14 hours**, **18 hours** is an unnecessarily strict limit for PEP initiation. - Guidelines universally support starting PEP up to **72 hours** post-exposure for optimal benefit [1].

Question 1248: What is the most significant risk factor for transitional cell carcinoma of the bladder?

A. Schistosomiasis (Correct Answer)
B. Ascariasis
C. Malaria
D. None of the options

Explanation: ***Schistosomiasis*** - Schistosomiasis, especially caused by *Schistosoma haematobium*, is strongly associated with the development of **transitional cell carcinoma** of the bladder. - The inflammation and chronic irritation of the bladder epithelium by the parasite lead to increased risk of **malignant transformation**. *None* - This option implies that there are **no known causes**, which is incorrect, as there are well-established associations, particularly with schistosomiasis. - Transitional cell carcinoma of the bladder has **known risk factors** and associations, contrary to this option's suggestion. *Ascariasis* - Ascariasis is primarily an **intestinal infection** caused by *Ascaris lumbricoides* and is not linked to bladder cancer. - It is more associated with **pulmonary symptoms** or intestinal obstruction rather than urothelial malignancies. *Malaria* - Malaria is caused by *Plasmodium* species and typically results in **fever** and **splenomegaly**, not bladder cancer. - There is no significant association between malaria infections and the development of **transitional cell carcinoma**.

Question 1249: All of the following provide protection against malaria except which of the following?

A. PNH (Correct Answer)
B. Sickle cell anemia
C. Hereditary spherocytosis
D. Duffy blood group

Explanation: ***PNH*** - Paroxysmal Nocturnal Hemoglobinuria (PNH) does not provide any **protection against malaria**; it is an acquired bone marrow disorder. - While it leads to increased hemolysis and thrombosis, it does not affect **malaria susceptibility** directly. *Duffy blood group* - The Duffy blood group has specific antigens that are a **receptor for Plasmodium vivax**, making individuals with a Duffy-negative phenotype resistant to this type of malaria. - Therefore, Duffy blood group status can indeed serve as a protective factor against certain malaria strains. *Hereditary spherocytosis* - This condition results in **spherical red blood cells** [1], causing hemolytic anemia, but it does not confer protection against malaria. - People with hereditary spherocytosis do not have a lower prevalence of malaria and may still be susceptible to infection. *Sickle cell anemia* - Individuals with sickle cell anemia often exhibit **increased resistance to malaria**, especially against Plasmodium falciparum [2]. - The sickling of red blood cells under low oxygen conditions creates an unfavorable environment for the malarial parasites to thrive [2, 3].

Question 1250: Procalcitonin is considered a marker for:

A. Sepsis (Correct Answer)
B. Medullary thyroid carcinoma
C. Parathyroid adenoma
D. Vitamin D resistant rickets

Explanation: **Sepsis** - **Procalcitonin** (PCT) levels significantly rise in response to bacterial infections and **sepsis**, making it a useful diagnostic and prognostic marker. - Its levels correlate with the severity of bacterial infection and can help differentiate bacterial from viral etiologies. *Medullary thyroid carcinoma* - **Medullary thyroid carcinoma** (MTC) is characterized by the production of **calcitonin**, a different hormone from procalcitonin, by the parafollicular C cells of the thyroid. - While calcitonin is a tumor marker for MTC, **procalcitonin** is not. *Vitamin D resistant rickets* - **Vitamin D resistant rickets** (also known as X-linked hypophosphatemia) is a genetic disorder characterized by impaired phosphate reabsorption in the kidneys [1]. - It is associated with low phosphate levels and bone deformities, but not with elevated procalcitonin [1]. *Parathyroid adenoma* - A **parathyroid adenoma** leads to primary hyperparathyroidism, characterized by excessive production of **parathyroid hormone (PTH)** [1]. - This results in hypercalcemia and hypophosphatemia, with no direct link to procalcitonin levels [1].

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

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HIV/AIDS and Related Infections

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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Healthcare-Associated Infections

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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