Infectious Diseases Practice Questions

Q: What is the most common malignancy in AIDS patients?

Kaposi sarcoma. **Explanation:** **Kaposi Sarcoma (KS)** is the most common malignancy associated with HIV/AIDS [1]. It is caused by **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi Sarcoma-associated Herpesvirus (KSHV). In the context of AIDS, it typically presents as painless, violaceous (purple) macules, plaques, or nodules on the skin, mucous membranes, or visceral organs [1]. It is considered an **AIDS-defining illness** [1]. While the incidence has significantly decreased with the advent of Highly Active Antiretroviral Therapy (HAART), it remains the most frequent neoplasm in this population. **Analysis of Incorrect Options:** * **B. Hodgkin Lymphoma:** While HIV patients have a significantly higher risk of Hodgkin Lymphoma compared to the general population, it is less common than Kaposi Sarcoma. Note that **Non-Hodgkin Lymphoma (NHL)**, specifically Burkitt and Diffuse Large B-cell Lymphoma, is the *second* most common malignancy in AIDS. * **C. Leukemia:** There is no strong epidemiological link between HIV and an increased incidence of primary leukemias compared to the general population. * **D. Multiple Myeloma:** Although plasma cell dyscrasias can occur in HIV patients due to chronic B-cell stimulation, it is not a defining or common malignancy in this group. **High-Yield Clinical Pearls for NEET-PG:** 1. **Top 3 AIDS-Defining Malignancies:** 1. Kaposi Sarcoma, 2. Non-Hodgkin Lymphoma, 3. Invasive Cervical Carcinoma. 2. **Histology of KS:** Characterized by **spindle-shaped cells**, slit-like vascular spaces, and extravasated RBCs. 3. **Most common site:** The skin is most common, but the **gastrointestinal tract** and lungs are common visceral sites [1]. 4. **Primary Effusion Lymphoma:** Another HHV-8 associated malignancy seen specifically in AIDS patients.

Q: Epstein-Barr Virus (EBV) is associated with which of the following malignancies?

Nasopharyngeal carcinoma. **Epstein-Barr Virus (EBV)**, also known as Human Herpesvirus 4 (HHV-4), is a potent oncogenic virus with a strong tropism for B-lymphocytes and epithelial cells. **Why Nasopharyngeal Carcinoma (NPC) is correct:** EBV is etiologically linked to the undifferentiated type of **Nasopharyngeal Carcinoma** (WHO Type III) [1]. The virus establishes a latent infection in the nasopharyngeal epithelial cells. The expression of viral oncogenes, specifically **LMP-1** (Latent Membrane Protein-1), mimics CD40 signaling, leading to constitutive activation of cell survival pathways (like NF-κB) and malignant transformation. This association is particularly prevalent in Southern China and parts of Africa [1]. **Analysis of Incorrect Options:** * **A & B (Larynx and Bladder Carcinoma):** These malignancies are primarily associated with risk factors like tobacco smoking, alcohol (larynx), and chemical exposures/Schistosomiasis (bladder). There is no established causal link between EBV and these cancers. * **D (Chronic Lymphocytic Leukemia):** CLL is a mature B-cell neoplasm not associated with EBV. However, EBV is strongly linked to other B-cell malignancies like **Burkitt Lymphoma**, **Hodgkin Lymphoma**, and **Post-transplant lymphoproliferative disorder (PTLD)** [1]. **High-Yield Clinical Pearls for NEET-PG:** * **EBV-Associated Malignancies:** Remember the mnemonic **"B-H-N"**: **B**urkitt Lymphoma (starry-sky appearance, t(8;14)), **H**odgkin Lymphoma (Mixed cellularity subtype), and **N**asopharyngeal Carcinoma [1]. * **Other Associations:** Infectious Mononucleosis (Heterophile positive), Oral Hairy Leukoplakia (in HIV), and Gastric Carcinoma (subset). * **Diagnostic Marker:** Elevated titers of antibodies against **EBNA** (EBV Nuclear Antigen) and **VCA** (Viral Capsid Antigen) are used clinically. For NPC specifically, **IgA antibodies to VCA** are a useful screening marker.

Q: A 22-year-old female presented to the emergency department with a 4-day history of nausea, vomiting, and watery diarrhea, accompanied by a low-grade fever. She was hospitalized, treated symptomatically, and improved. Blood cultures were obtained during her admission. Upon follow-up, the blood culture results revealed the presence of Clostridium perfringens. As her physician, what is your next instruction to the patient?

Return for intravenous penicillin therapy.. ### Explanation **1. Why Option C is Correct:** The presence of *Clostridium perfringens* in a blood culture is never considered a contaminant; it represents a medical emergency. Even if the patient appears clinically improved, **Clostridial bacteremia** carries a high risk of rapid deterioration due to potential complications like gas gangrene (myonecrosis) or massive hemolysis. The standard of care is immediate hospitalization for **intravenous Penicillin G** (often combined with Clindamycin to inhibit toxin production). The patient must be recalled urgently to ensure the infection is eradicated and to monitor for occult deep-seated foci. **2. Why Other Options are Wrong:** * **Option A:** While *Clostridium septicum* bacteremia is strongly associated with colon cancer (requiring a colonoscopy), *C. perfringens* is more commonly associated with hepatobiliary disease, skin/soft tissue infections, or contaminated food. Colonoscopy is not the immediate priority here. * **Option B:** Waiting for a repeat blood culture is dangerous. Clostridial infections can progress to fatal sepsis within hours. Treatment must be initiated based on the initial positive culture. * **Option D:** Echocardiography is indicated for *Streptococcus bovis* or *Enterococcus* bacteremia to rule out endocarditis. It is not a routine requirement for *C. perfringens* bacteremia. **3. NEET-PG High-Yield Pearls:** * **C. perfringens:** Most common cause of gas gangrene (myonecrosis) and food poisoning (Type A strains). * **Double Zone of Hemolysis:** A classic laboratory finding on blood agar for *C. perfringens*. * **Nagler’s Reaction:** Used to identify the **Alpha-toxin** (lecithinase) produced by *C. perfringens*. * **Association Rule:** * *C. septicum* + Bacteremia = Look for **Colon Cancer**. * *S. bovis* + Bacteremia = Look for **Colon Cancer**. * *C. perfringens* + Bacteremia = Immediate **IV Penicillin**.

Q: Which of the following is NOT a diagnostic criterion for infective endocarditis?

Erythrocyte Sedimentation Rate (ESR). The diagnosis of Infective Endocarditis (IE) is primarily based on the **Modified Duke Criteria**, which categorizes findings into Major and Minor criteria [1]. **Why ESR is the correct answer:** While the Erythrocyte Sedimentation Rate (ESR) is frequently elevated in patients with IE due to chronic inflammation [3], it is **not** included in the Modified Duke Criteria. It is a highly non-specific marker and lacks the diagnostic weight required to confirm or suggest endocarditis in a clinical setting. **Analysis of other options:** * **Rheumatoid Factor (RF):** This is a recognized **Minor Criterion** under the "Immunologic phenomena" category. Other immunologic markers include glomerulonephritis, Osler’s nodes, and Roth’s spots. * **Positive Blood Culture:** This is a **Major Criterion** [1]. To meet this, one must demonstrate typical microorganisms (e.g., *S. viridans*, *S. aureus*, HACEK) from two separate blood cultures [1]. * **Positive Echocardiogram (ECG/ECHO):** Note that in medical exams, "ECG" is occasionally used as a typo for "ECHO" or refers to the **Major Criterion** of "Evidence of endocardial involvement" (e.g., vegetation, abscess, or new valvular regurgitation) visualized via Echocardiography [1]. **NEET-PG High-Yield Pearls:** * **Modified Duke Criteria:** Diagnosis requires 2 Major OR 1 Major + 3 Minor OR 5 Minor criteria [1]. * **Most Common Cause:** *Staphylococcus aureus* is now the most common cause globally (acute IE), while *Streptococcus viridans* remains common in subacute cases. * **Culture-Negative IE:** Most commonly caused by prior antibiotic use or fastidious organisms like *Coxiella burnetii* (Q fever) [2]. * **Janeway Lesions vs. Osler Nodes:** Janeway lesions are painless/embolic (Minor criteria: Vascular phenomena); Osler nodes are painful/immunologic (Minor criteria: Immunologic phenomena).

Q: Pancytopenia is most common after which condition?

Hepatitis. Explanation: The correct answer is **Hepatitis**. This refers to the clinical entity known as **Aplastic Anemia-Hepatitis Syndrome**. **1. Why Hepatitis is Correct:** Pancytopenia (a reduction in RBCs, WBCs, and platelets) is a well-recognized, severe complication of acute viral hepatitis [1]. It typically manifests as **Aplastic Anemia** occurring 2–3 months after an episode of acute hepatitis. While it can be associated with Hepatitis B and C, it is most frequently linked to **non-A, non-B, non-C, non-E (seronegative) hepatitis** [1]. The underlying mechanism is thought to be an immune-mediated destruction of hematopoietic stem cells by activated T-lymphocytes, triggered by the preceding viral infection. **2. Why Other Options are Incorrect:** * **Infective Endocarditis:** Typically presents with anemia of chronic disease and occasionally leukocytosis or thrombocytopenia (due to splenomegaly), but generalized bone marrow failure (pancytopenia) is not a standard feature. * **Pyelonephritis:** This is a localized bacterial infection of the kidney. It causes neutrophilic leukocytosis. It does not affect the bone marrow to cause pancytopenia. * **Meningitis:** Acute bacterial or viral meningitis causes pleocytosis in the CSF and systemic leukocytosis, but it does not lead to the suppression of all three cell lines. **High-Yield Clinical Pearls for NEET-PG:** * **Aplastic Anemia-Hepatitis Syndrome** is most common in young males. * The hepatitis is usually resolving or has resolved by the time pancytopenia develops. * **Other infections causing pancytopenia:** HIV, Parvovirus B19 (pure red cell aplasia or aplastic crisis in sickle cell), Tuberculosis (miliary), and Leishmaniasis (Kala-azar). * **Drug-induced pancytopenia:** Chloramphenicol is the classic board-exam culprit.

Q: What is the antibiotic of choice for the prophylaxis of endocarditis in adults undergoing dental procedures, considering penicillin allergy and inability to take oral medication?

Clindamycin 600 mg 30 minutes before dental procedures. **Explanation:** The primary objective of Infective Endocarditis (IE) prophylaxis is to prevent bacteremia (specifically *Viridans group streptococci*) during invasive dental procedures in high-risk patients. [1] **Why Option D is Correct:** According to the AHA/IDSA guidelines, for patients who are **allergic to Penicillin** and **unable to take oral medications**, the parenteral drug of choice is **Clindamycin (600 mg IV/IM)** administered 30–60 minutes before the procedure. Clindamycin provides excellent coverage against Gram-positive cocci and achieves high tissue concentrations. [2] (Note: While some recent guidelines have moved away from Clindamycin due to *C. difficile* concerns, it remains a classic standard in NEET-PG curriculum). **Analysis of Incorrect Options:** * **Option A (Clarithromycin):** This is an oral macrolide. While used for penicillin-allergic patients, it is incorrect here because the patient is specified as "unable to take oral medication." * **Options B & C (Cephalexin/Cefadroxil):** These are first-generation cephalosporins. They are contraindicated in patients with a history of **anaphylaxis, angioedema, or urticaria** related to penicillin due to the risk of cross-reactivity. [3] Furthermore, these are oral formulations. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Prophylaxis:** Amoxicillin 2g PO (1 hour before). * **Unable to take Oral (No Allergy):** Ampicillin 2g IV/IM or Cefazolin/Ceftriaxone 1g IV/IM. * **Penicillin Allergy (Oral):** Cephalexin, Clindamycin, or Azithromycin/Clarithromycin. * **High-Risk Conditions requiring prophylaxis:** Prosthetic heart valves, prior IE, Cyanotic Congenital Heart Disease (unrepaired), and Cardiac transplant recipients with valve regurgitation. [1] * **Procedures:** Only those involving manipulation of gingival tissue, periapical region of teeth, or perforation of oral mucosa.

Q: A 33-year-old man has never been vaccinated for hepatitis B. Serologic tests reveal negative hepatitis B surface antigen (HBsAg) and positive antibody to surface antigen. Which of the following conditions does this serologic pattern best fit with?

Previous hepatitis B infection. ### Explanation The patient’s serologic profile shows **HBsAg negative** and **Anti-HBs positive**. This pattern indicates immunity to Hepatitis B. In the context of the options provided, this is most consistent with a **resolved previous infection** [1]. **1. Why Option A is Correct:** When a person recovers from a natural Hepatitis B infection, the surface antigen (HBsAg) disappears from the blood, and the body produces protective antibodies against it (Anti-HBs) [1]. Crucially, in a **previous infection**, the patient would also typically be positive for **Anti-HBc (IgG)** [1]. While the question doesn't mention Anti-HBc, the presence of Anti-HBs in a non-vaccinated individual is the hallmark of recovery and subsequent immunity. **2. Why the Other Options are Incorrect:** * **B. Chronic Active Hepatitis:** This would require **HBsAg** to be present for more than 6 months [1]. Anti-HBs is generally absent in chronic states as the virus has not been cleared. * **C. Acute Hepatitis B Infection:** The first marker to appear in acute infection is **HBsAg** [1]. Anti-HBs only appears during the convalescence phase after HBsAg has cleared. * **D. Poor Prognosis:** The presence of Anti-HBs signifies a **good prognosis**, as it indicates viral clearance and long-term immunity. **3. NEET-PG High-Yield Pearls:** * **Vaccination vs. Infection:** Both show positive Anti-HBs. However, **Vaccinated** patients are **Anti-HBc negative**, while those with **Previous Infection** are **Anti-HBc positive** [1]. * **Window Period:** This is the interval where HBsAg has disappeared but Anti-HBs has not yet appeared. The only marker present is **Anti-HBc IgM** [1]. * **HBeAg:** Indicates high viral replication and high infectivity. * **Anti-HBs:** The only serologic marker that confers immunity [1].

Q: A 40-year-old diabetic patient presents with proptosis of one eye and a black eschar over the palate. What is the likely causative organism?

Mucor. ### Explanation The clinical presentation of **proptosis** and a **black necrotic eschar** on the palate in a **diabetic patient** (especially one in ketoacidosis) is the classic triad for **Rhinocerebral Mucormycosis** [1]. **Why Mucor is the correct answer:** Mucormycosis is caused by fungi of the order Mucorales (e.g., *Rhizopus*, *Mucor*). These fungi are **angioinvasive**, meaning they invade blood vessel walls, leading to thrombosis, tissue ischemia, and necrosis [1]. This necrosis manifests clinically as a characteristic **black eschar** on the nasal mucosa or palate. The infection spreads rapidly from the sinuses to the orbit (causing proptosis and ophthalmoplegia) and eventually to the brain. **Why the other options are incorrect:** * **Pseudomonas:** While it can cause "Malignant Otitis Externa" in diabetics (involving the ear canal and skull base), it does not typically present with a palatal eschar or acute rhino-orbital syndrome. * **Candida:** Usually causes superficial infections like oral thrush (white plaques) or systemic candidiasis. It is not angioinvasive enough to cause rapid tissue necrosis and eschar formation [2]. * **E. coli:** A common cause of urinary tract infections and sepsis in diabetics, but it does not have a predilection for the paranasal sinuses or cause necrotic facial lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factors:** Uncontrolled Diabetes Mellitus (Ketoacidosis), Neutropenia, and Iron overload (Deferoxamine use) [1]. * **Diagnosis:** KOH mount or biopsy showing **broad, ribbon-like, non-septate hyphae** with **right-angle (90°) branching**. * **Management:** Immediate surgical debridement + Intravenous **Liposomal Amphotericin B** [1]. (Note: Azoles like Fluconazole are ineffective; Posaconazole/Isavuconazole are alternatives).

Question 1

What is the most common malignancy in AIDS patients?

Accepted Answer

Kaposi sarcoma

Answer

Hodgkin lymphoma

Answer

Leukemia

Answer

Multiple myeloma

Question 2

Acute infectious purpura fulminans is caused by which of the following agents?

Accepted Answer

Neisseria meningitidis and varicella

Answer

Gonococci

Answer

E. coli

Answer

Proteus

Question 3

Epstein-Barr Virus (EBV) is associated with which of the following malignancies?

Accepted Answer

Nasopharyngeal carcinoma

Answer

Carcinoma of the larynx

Answer

Carcinoma of the bladder

Answer

Chronic lymphocytic leukemia

Question 4

What is the recommended treatment regimen for Brucella infection according to WHO guidelines?

Accepted Answer

Rifampicin with doxycycline

Answer

Streptomycin with doxycycline

Answer

Rifampicin with ciprofloxacin

Answer

Streptomycin with erythromycin

Question 5

A 22-year-old female presented to the emergency department with a 4-day history of nausea, vomiting, and watery diarrhea, accompanied by a low-grade fever. She was hospitalized, treated symptomatically, and improved. Blood cultures were obtained during her admission. Upon follow-up, the blood culture results revealed the presence of Clostridium perfringens. As her physician, what is your next instruction to the patient?

Accepted Answer

Return for intravenous penicillin therapy.

Answer

Intravenous penicillin therapy plus colonoscopy.

Answer

Return for blood culture.

Answer

Intravenous penicillin therapy plus echocardiography.

Question 6

Which of the following is NOT a diagnostic criterion for infective endocarditis?

Accepted Answer

Erythrocyte Sedimentation Rate (ESR)

Answer

Rheumatoid factor

Answer

Positive blood culture

Answer

Positive electrocardiogram (ECG)

Question 7

Pancytopenia is most common after which condition?

Accepted Answer

Hepatitis

Answer

Infective carditis

Answer

Pyelonephritis

Answer

Meningitis

Question 8

What is the antibiotic of choice for the prophylaxis of endocarditis in adults undergoing dental procedures, considering penicillin allergy and inability to take oral medication?

Accepted Answer

Clindamycin 600 mg 30 minutes before dental procedures

Answer

Clarithromycin 500 mg 1 hour before dental procedures

Answer

Cephalexin 2 g 1 hour before dental procedures

Answer

Cefadroxil 2 g 1 hour before dental procedures

Question 9

A 33-year-old man has never been vaccinated for hepatitis B. Serologic tests reveal negative hepatitis B surface antigen (HBsAg) and positive antibody to surface antigen. Which of the following conditions does this serologic pattern best fit with?

Accepted Answer

Previous hepatitis B infection

Answer

Chronic active hepatitis

Answer

Acute hepatitis B infection

Answer

Poor prognosis

Question 10

A 40-year-old diabetic patient presents with proptosis of one eye and a black eschar over the palate. What is the likely causative organism?

Accepted Answer

Mucor

Answer

Pseudomonas

Answer

Candida

Answer

E. coli

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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