Infectious Diseases Practice Questions

Q: Which of the following is not an AIDS-defining lesion?

Kaposi sarcoma. ### Explanation The classification of AIDS-defining illnesses is a high-yield topic for NEET-PG. These are specific opportunistic infections and malignancies that indicate a profound collapse of cell-mediated immunity (usually CD4 count <200 cells/µL) in an HIV-positive individual [1]. **Why the Correct Answer is D (Hodgkin’s Lymphoma):** *Note: There appears to be a clerical error in the provided prompt’s key. **Hodgkin’s Lymphoma is NOT an AIDS-defining lesion.** While its incidence is increased in HIV patients, it is not used to define the transition from HIV to AIDS. Conversely, Kaposi Sarcoma is one of the most classic AIDS-defining conditions. **Analysis of Options:** * **Kaposi Sarcoma (Option A):** A vascular tumor caused by HHV-8. It is a hallmark AIDS-defining illness, typically presenting as violaceous cutaneous nodules [1]. * **Histoplasmosis (Option B):** Disseminated or extrapulmonary histoplasmosis is classified as an AIDS-defining opportunistic fungal infection [1]. * **Burkitt Lymphoma (Option C):** High-grade B-cell lymphomas, including Burkitt’s, immunoblastic lymphoma, and primary CNS lymphoma, are all AIDS-defining malignancies [1]. * **Hodgkin’s Lymphoma (Option D):** Although HIV patients have a 5–10 fold higher risk of developing Hodgkin’s Lymphoma compared to the general population, it remains **non-AIDS-defining** according to CDC and WHO criteria [1]. **High-Yield Clinical Pearls for NEET-PG:** 1. **Most common AIDS-defining neoplasm:** Kaposi Sarcoma [1]. 2. **Most common AIDS-defining infection:** *Pneumocystis jirovecii* pneumonia (PCP). 3. **Cervical Cancer:** Only **Invasive** Cervical Cancer is AIDS-defining (Cervical Intraepithelial Neoplasia is not) [1]. 4. **Tuberculosis:** Both pulmonary and extrapulmonary TB are now considered AIDS-defining in HIV-positive individuals [1]. 5. **Wasting Syndrome:** Defined as >10% involuntary weight loss plus chronic diarrhea or weakness [1].

Q: Clindamycin is the drug of choice in which of the following?

Bacteroides fragilis. **Explanation:** **Clindamycin** is a lincosamide antibiotic that inhibits protein synthesis by binding to the 50S ribosomal subunit. It is classically known for its excellent activity against **Gram-positive cocci** and **anaerobes**. [1] 1. **Why Bacteroides fragilis is correct:** Clindamycin is historically the drug of choice for anaerobic infections occurring **above the diaphragm** (e.g., lung abscess, aspiration pneumonia). While resistance is increasing, it remains a primary agent for treating *Bacteroides fragilis* and other anaerobes in skin, soft tissue, and oral cavity infections. 2. **Why other options are incorrect:** * **MRSA:** While Clindamycin can be used for community-acquired MRSA (CA-MRSA) skin infections, it is not the "drug of choice." [1] Vancomycin remains the gold standard for systemic MRSA. [2] * **Mycoplasma pneumoniae:** This is an atypical bacterium lacking a cell wall. The drugs of choice are Macrolides (Azithromycin) or Tetracyclines (Doxycycline). * **Pseudomonas:** This is a Gram-negative aerobe. Clindamycin has **zero activity** against aerobic Gram-negative bacilli like *Pseudomonas*. Antipseudomonal penicillins (Piperacillin) or Cephalosporins (Ceftazidime) are required. [3] **High-Yield NEET-PG Pearls:** * **The "Diaphragm Rule":** Use **Clindamycin** for anaerobes *above* the diaphragm (aspiration pneumonia) and **Metronidazole** for anaerobes *below* the diaphragm (intra-abdominal infections). * **D-Test:** Used to detect inducible clindamycin resistance in Staphylococci. A positive test (D-shaped zone) indicates the presence of the *erm* gene; Clindamycin should not be used. * **Side Effect:** Clindamycin is the antibiotic most classically associated with **Pseudomembranous colitis** caused by *Clostridioides difficile*.

Q: Which of the following types of Kaposi sarcoma is associated with HIV?

None of the above. **Explanation:** The correct answer is **None of the above** because the type of Kaposi Sarcoma (KS) associated with HIV is specifically classified as **Epidemic Kaposi Sarcoma** (also known as AIDS-associated KS) [1]. Kaposi Sarcoma is a multicentric angioproliferative tumor caused by **Human Herpesvirus 8 (HHV-8)** [1]. While all forms of KS are linked to HHV-8, they are categorized into four distinct clinical-epidemiological types: * **Epidemic (AIDS-associated) KS:** This is the most common and aggressive form. It occurs in HIV-infected individuals, typically when CD4 counts are low [1]. It often involves the skin, mucous membranes (especially the hard palate), and viscera [1]. * **Classic KS (Option B & C):** This type typically affects elderly men of Mediterranean, Eastern European, or Jewish descent. It is usually indolent, presenting as slow-growing lesions on the lower extremities. "European KS" is simply a geographic descriptor for the Classic type. * **Endemic (African) KS (Option A):** This occurs in HIV-negative individuals in equatorial Africa [1]. It presents in two forms: an indolent cutaneous form in adults and a highly aggressive lymphadenopathic form in children. * **Iatrogenic (Transplant-associated) KS:** Occurs in patients on chronic immunosuppressive therapy, particularly following solid organ transplantation. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site of involvement:** Skin (lower extremities in Classic; face/trunk in Epidemic). * **Most common oral site:** Hard palate [1]. * **Histopathology:** Characterized by **spindle-shaped cells**, slit-like vascular spaces, and extravasated RBCs. * **Treatment:** Highly Active Antiretroviral Therapy (HAART) is the mainstay for Epidemic KS; systemic chemotherapy (e.g., Liposomal Doxorubicin) is used for advanced disease.

Q: All of the following are seen in severe Falciparum malaria infection EXCEPT?

Hyperglycemia. Severe Falciparum malaria is a medical emergency characterized by vital organ dysfunction and high parasite counts. [1] **1. Why Hyperglycemia is the Correct Answer (The Exception):** In severe malaria, **Hypoglycemia** (not hyperglycemia) is a common and dangerous complication. It occurs due to two primary mechanisms: * **Host factors:** Failure of hepatic gluconeogenesis and increased consumption of glucose by both the host and the parasites. * **Drug-induced:** Quinine and quinidine (traditionally used for treatment) [1] are potent stimulators of pancreatic insulin secretion, leading to hyperinsulinemic hypoglycemia. **2. Analysis of Incorrect Options (Features of Severe Malaria):** * **Severe Anemia (Option A):** Defined as a hemoglobin <5 g/dL or hematocrit <15%. It results from the direct destruction of parasitized RBCs, splenic clearance of non-parasitized RBCs, and bone marrow suppression. [1] * **Renal Failure (Option B):** Acute Kidney Injury (AKI) is common in adults, often presenting as "Blackwater Fever" (hemoglobinuria) due to massive intravascular hemolysis or acute tubular necrosis. * **Acidosis (Option D):** Metabolic acidosis (pH 3 mg/dL), and Hyperparasitemia (>10% or 500,000/μL). [1] * **Drug of Choice:** Intravenous **Artesunate** is the gold standard for severe malaria. [1] * **Sequestration:** The hallmark of *P. falciparum* is "cytoadherence," where infected RBCs stick to vascular endothelium, causing organ ischemia. [1]

Q: Zidovudine toxicity is increased by all except?

Azithromycin. **Explanation:** Zidovudine (AZT), a Nucleoside Reverse Transcriptase Inhibitor (NRTI), is primarily metabolized in the liver via **glucuronidation** (by UDP-glucuronosyltransferase) and excreted by the kidneys. Toxicity, characterized by bone marrow suppression (anemia and neutropenia), increases when its metabolism or excretion is inhibited. **Why Azithromycin is the correct answer:** Azithromycin is a macrolide antibiotic that, unlike Erythromycin or Clarithromycin, **does not inhibit the Cytochrome P450 system** or interfere with the glucuronidation pathway. Therefore, it does not significantly increase the plasma levels or toxicity of Zidovudine. **Analysis of incorrect options:** * **Probenecid:** It inhibits both the hepatic glucuronidation and the renal tubular secretion of Zidovudine, leading to significantly increased plasma levels and risk of toxicity. * **Cisplatin:** This chemotherapeutic agent is nephrotoxic. By impairing renal function, it reduces the clearance of Zidovudine. Furthermore, both drugs cause additive bone marrow suppression. * **Paracetamol (Acetaminophen):** It is also metabolized via glucuronidation. Competitive inhibition for the same enzyme pathway can decrease Zidovudine metabolism, potentially increasing its toxicity (though clinical significance varies). **High-Yield Clinical Pearls for NEET-PG:** * **Most common side effect of Zidovudine:** Macrocytic anemia and bone marrow suppression. * **Drug of choice for preventing vertical transmission** of HIV (mother-to-child) during labor is Zidovudine. * **L-type interaction:** Drugs like Ganciclovir and Amphotericin B also increase Zidovudine toxicity due to additive hematotoxicity and nephrotoxicity respectively. * **Nail hyperpigmentation** is a characteristic physical finding associated with chronic Zidovudine use.

Question 1

Which of the following is not an AIDS-defining lesion?

Accepted Answer

Kaposi sarcoma

Answer

Histoplasmosis

Answer

Burkitt lymphoma

Answer

Hodgkin's lymphoma

Question 2

An adult male with a history of pneumonia, who is unconscious and has a 10-year history of alcoholism, requires treatment. What is the drug of choice for treating pneumonia in this patient?

Accepted Answer

Inj Clindamycin 600mg

Answer

Tab Amoxicillin 500mg

Answer

Tab Azithromycin 500mg

Answer

Inj Levofloxacin 500mg

Question 3

A 25-year-old man presented with fever, cough, expectoration, and breathlessness of 2 months' duration. Contrast-enhanced computed tomography of the chest showed bilateral upper lobe fibrotic lesions and mediastinal enlarged necrotic nodes with peripheral rim enhancement. Which one of the following is the most probable diagnosis?

Accepted Answer

Tuberculosis

Answer

Sarcoidosis

Answer

Lymphoma

Answer

Silicosis

Question 4

A 46-year-old male with HIV and severe penicillin allergy, receiving zidovudine, indinavir, and stavudine, presents with fever, nonproductive cough, and severe hypoxia. Chest x-ray reveals diffuse increased interstitial markings and a possible lobar consolidation in the left lower lobe. After appropriate evaluation, the patient receives levofloxacin, trimethoprim-sulfamethoxazole, and acyclovir. Initial serum creatinine is 1.6 mg/dL. On day 4, it has risen to 3.8 mg/dL and a normal serum potassium has risen to 7.1 mg/dL. Urinalysis reveals no casts, 10 to 20 WBC/HPF, and rare RBCs. Which drug is the most likely cause of renal failure?

Accepted Answer

Trimethoprim-sulfamethoxazole

Answer

Levofloxacin

Answer

Acyclovir

Answer

Indinavir

Question 5

Clindamycin is the drug of choice in which of the following?

Accepted Answer

Bacteroides fragilis

Answer

Methicillin-resistant Staphylococcus aureus (MRSA)

Answer

Mycoplasma pneumoniae

Answer

Pseudomonas infection

Question 6

A 52-year-old male presented with purpura, arthralgia, neuropathy, and glomerulonephritis. Blood routine examination revealed low hemoglobin and high ESR, with mild alteration in LFT and mild transaminase elevation. He has a history of blood transfusion in 1987 following an accident. What is the underlying pathology in this clinical setting?

Accepted Answer

Essential mixed cryoglobulinemia

Answer

Henoch-Schonlein purpura

Answer

Amyloidosis

Answer

Chronic infection with malaria

Question 7

Toxic shock syndrome caused by Staphylococcus is due to which of the following?

Accepted Answer

Superantigens

Answer

Hemolytic antigen

Answer

Hyaluronidase

Answer

Coagulase

Question 8

Which of the following types of Kaposi sarcoma is associated with HIV?

Accepted Answer

None of the above

Answer

Endemic Kaposi sarcoma

Answer

Classic Kaposi sarcoma

Answer

European Kaposi sarcoma

Question 9

All of the following are seen in severe Falciparum malaria infection EXCEPT?

Accepted Answer

Hyperglycemia

Answer

Severe normocytic normochromic anemia

Answer

Renal failure

Answer

Acidemia/acidosis

Question 10

Zidovudine toxicity is increased by all except?

Accepted Answer

Azithromycin

Answer

Probenecid

Answer

Cisplatin

Answer

Paracetamol

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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