Infectious Diseases Practice Questions

Q: Which of the following statements regarding Pneumocystis jirovecii pneumonia (PCP) is/are true? 1. Bronchoscopy with bronchoalveolar lavage (BAL) is the mainstay of diagnosis for PCP. 2. Pneumatoceles are seen in all cases of PCP. 3. A CD4 count < 350 cells/µL is an indication for prophylaxis against PCP. 4. Trimethoprim-sulfamethoxazole is the drug of choice for prophylaxis.

1 - True, 2 - False, 3 - False, 4 - True. **Explanation:** **1. Bronchoscopy with BAL is the mainstay of diagnosis (True):** *Pneumocystis jirovecii* cannot be cultured. Diagnosis relies on microscopic visualization of cysts or trophic forms in respiratory specimens [1]. While induced sputum is the initial non-invasive step, **Bronchoalveolar Lavage (BAL)** is the gold standard diagnostic procedure due to its high sensitivity (>90-95%) [1]. **2. Pneumatoceles are seen in all cases (False):** The classic radiological finding in PCP is **bilateral diffuse ground-glass opacities** (perihilar distribution). While pneumatoceles (thin-walled air-filled cysts) can occur and increase the risk of spontaneous pneumothorax, they are seen in only about 10-20% of cases, not all [1]. **3. CD4 count < 350 cells/µL is the indication for prophylaxis (False):** In HIV-infected patients, primary prophylaxis for PCP is indicated when the **CD4 count falls below 200 cells/µL** (or if there is a history of oropharyngeal candidiasis) [1]. A threshold of 350 cells/µL is too high for initiating PCP-specific prophylaxis. **4. Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice (True):** TMP-SMX is the first-line agent for both the **treatment and prophylaxis** of PCP [1]. It is highly effective and also provides cross-protection against Toxoplasmosis. **High-Yield Clinical Pearls for NEET-PG:** * **Stains:** Use **Gomori Methenamine Silver (GMS)** to see crushed-ping-pong-ball shaped cysts or **Giemsa** for trophic forms [1]. * **Biomarker:** Elevated **Serum Beta-D-Glucan** has high sensitivity (negative predictive value) for PCP [2]. * **Steroids:** Indicated in treatment if **PaO2 35 mmHg to prevent inflammatory worsening [1]. * **Alternative for Prophylaxis:** Dapsone or Atovaquone (if sulfa-allergic) [1].

Q: What is the most likely diagnosis for this 19-month-old girl who presented with a 1-week history of an ascending erythematous eruption?

Herpes zoster. **Explanation:** The correct diagnosis is **Herpes Zoster (Shingles)**. While commonly associated with the elderly, Herpes Zoster can occur in children, especially those who were infected with Varicella Zoster Virus (VZV) in utero or during the first year of life. The "ascending erythematous eruption" in this clinical scenario refers to a **dermatomal distribution**. Herpes Zoster is caused by the reactivation of latent VZV from the dorsal root ganglia. In pediatric patients, the presentation is often milder than in adults, frequently lacking the classic prodromal pain or post-herpetic neuralgia, which can make the diagnosis challenging if the clinician only expects "adult-type" symptoms. **Why the other options are incorrect:** * **Cellulitis:** This typically presents as a spreading, poorly demarcated area of skin erythema, warmth, and edema. It does not follow a dermatomal pattern and is usually associated with systemic signs like high fever. * **Hand, Foot, and Mouth Disease (HFMD):** Caused by Coxsackievirus A16, this presents with vesicular lesions on the palms, soles, and oral mucosa. It is not dermatomal or "ascending" in a linear nerve distribution. * **Lymphadenitis:** This refers to the inflammation/infection of lymph nodes. While it may cause localized swelling and redness, it does not present as a vesicular or erythematous eruption following a nerve path. **NEET-PG High-Yield Pearls:** * **Risk Factor:** The single greatest risk factor for pediatric Herpes Zoster is **primary varicella infection before age 1**. * **Distribution:** The most common sites in children are the **thoracic** and **lumbar** dermatomes. * **Diagnosis:** Usually clinical; however, the **Tzanck smear** (showing multinucleated giant cells) or PCR are definitive. * **Management:** In healthy children, the condition is often self-limiting; acyclovir is reserved for immunocompromised patients or severe cases.

Question 1

A 28-year-old woman presented with high-grade fever, cough, diarrhea, and mental confusion for 4 days. Chest X-ray revealed bilateral pneumonitis. What etiology is most likely?

Accepted Answer

Legionella pneumophila

Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Question 2

A rash appeared 9 hours after a scuba dive. What is the diagnosis?

Accepted Answer

Decompression sickness

Answer

Jellyfish envenomation

Answer

Mycobacterium marinum infection

Answer

Phylum Porifera contact dermatitis

Question 3

Which of the following statements regarding Pneumocystis jirovecii pneumonia (PCP) is/are true? 1. Bronchoscopy with bronchoalveolar lavage (BAL) is the mainstay of diagnosis for PCP. 2. Pneumatoceles are seen in all cases of PCP. 3. A CD4 count < 350 cells/µL is an indication for prophylaxis against PCP. 4. Trimethoprim-sulfamethoxazole is the drug of choice for prophylaxis.

Accepted Answer

1 - True, 2 - False, 3 - False, 4 - True

Answer

1 - False, 2 - True, 3 - True, 4 - False

Answer

1 - True, 2 - True, 3 - False, 4 - True

Answer

1 - False, 2 - False, 3 - True, 4 - False

Question 4

What is the most likely diagnosis for this 19-month-old girl who presented with a 1-week history of an ascending erythematous eruption?

Accepted Answer

Herpes zoster

Answer

Cellulitis

Answer

Hand, foot, and mouth disease

Answer

Lymphadenitis

Question 5

Fever increases water losses by ______ ml/day per degree Celsius?

Accepted Answer

200

Answer

100

Answer

400

Answer

800

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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