Infectious Diseases — MCQs

A young patient presented with fever (100 extdegree F), nausea, and vomiting. The patient also complained of vague abdominal discomfort. On general examination, icterus and hepatic tenderness were present. A family member had similar symptoms and was diagnosed with hepatitis E. Which of the following is the most likely route of transmission for the hepatitis E virus in this patient?

Q268Medium

A 35-year-old male patient with a known case of HIV on Antiretroviral Therapy complains of fever, dyspnea, dry cough, and weight loss for the past 3 months. The chest X-ray of the patient is as below. What is your diagnosis?

Q269Easy

All the following are used in the treatment of Pneumocystis jirovecii pneumonia except?

Q270Medium

A 22-year-old male military recruit complains of a headache and stiff neck. He is examined, blood is drawn, and a lumbar puncture is performed. The glucose in the CSF is 100 mg/dL and the serum glucose is 120 mg/dL. The CSF shows 3 lymphocytes and 0 neutrophils/microliter. Which of the following conclusions concerning the interpretation of these findings is most accurate?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 261: What is the most common pulmonary manifestation in AIDS?

A. Tuberculosis
B. Pneumonia (Correct Answer)
C. Bronchiectasis
D. Mycobacterium avium complex

Explanation: **Explanation:** The correct answer is **Pneumonia**. In patients with HIV/AIDS, the lung is the most common site of opportunistic infections. Among all pulmonary complications, **Bacterial Pneumonia** (specifically caused by *Streptococcus pneumoniae*) is the most frequent manifestation overall [3]. While *Pneumocystis jirovecii* pneumonia (PCP) is a classic AIDS-defining illness [2], pyogenic bacterial pneumonia occurs at a higher frequency across all CD4 counts [1]. **Analysis of Options:** * **A. Tuberculosis (TB):** TB is the most common **opportunistic infection** and the leading cause of death in HIV patients in developing countries like India [1]. However, in terms of general pulmonary "manifestations" or occurrences, bacterial pneumonia remains more frequent. * **C. Bronchiectasis:** This is a chronic structural complication resulting from recurrent infections (like TB or bacterial pneumonia) but is not the most common primary manifestation [3]. * **D. Mycobacterium avium complex (MAC):** This typically presents as a late-stage disseminated disease when CD4 counts drop below 50 cells/µL [4]. It is less common than both TB and bacterial pneumonia. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of community-acquired pneumonia in HIV:** *Streptococcus pneumoniae* [3]. * **Most common opportunistic infection (OI) in India:** Tuberculosis [1]. * **Most common AIDS-defining illness (globally):** *Pneumocystis jirovecii* pneumonia (PCP) [2]. * **Radiology Tip:** Bacterial pneumonia usually presents with focal lobar consolidation, whereas PCP typically shows bilateral perihilar ground-glass opacities [1]. * **CD4 Thresholds:** TB can occur at any CD4 level; PCP usually occurs at <200 cells/µL; MAC occurs at <50 cells/µL [4].

Question 262: Which of the following laboratory markers characterizes the recumbent stage of Hepatitis B?

A. Anti HBc (Correct Answer)
B. Anti HBs Ag
C. Anti HBe Ag
D. Anti HBV

Explanation: ### Explanation The "recumbent stage" (also known as the **Window Period**) of Hepatitis B is a critical diagnostic phase where HBsAg has disappeared from the blood, but Anti-HBs antibodies have not yet reached detectable levels [1]. **1. Why Anti-HBc is Correct:** During the window period, the only reliable serological marker of a recent HBV infection is **Anti-HBc IgM** (Antibody to Hepatitis B core antigen) [1]. Since HBsAg is negative and Anti-HBs is not yet present, testing for Anti-HBc is the only way to diagnose an acute infection during this gap [1]. **2. Why the Other Options are Incorrect:** * **Anti-HBs Ag:** This antibody appears during the **recovery/convalescence phase** and signifies immunity (either via natural infection or vaccination) [1]. In the recumbent stage, it is still below detectable limits. * **Anti-HBe Ag:** This indicates a decrease in viral replication and infectivity. While it may appear early, it is not the definitive marker used to define the window period. * **Anti-HBV:** This is a non-specific term. Diagnostic protocols specifically look for antibodies against specific components (Surface, Core, or e-antigen) rather than a generic "Anti-HBV." **3. NEET-PG High-Yield Pearls:** * **Window Period Markers:** HBsAg (-), Anti-HBs (-), **Anti-HBc IgM (+)** [1]. * **HBsAg:** The first marker to appear in blood (as early as 1–2 weeks post-exposure) [1]. * **Anti-HBs:** The only marker present in a **vaccinated** individual (Anti-HBc will be negative in vaccinated persons) [1]. * **Chronic Infection:** Defined by the persistence of HBsAg for >6 months [1]. * **HBeAg:** Indicates high viral replication and maximum infectivity.

Question 263: Fever, clubbing, and Osler's nodes are characteristic findings in which of the following conditions?

A. Typhoid fever
B. Rheumatic fever
C. Infective endocarditis (Correct Answer)
D. Leptospirosis

Explanation: **Explanation:** The correct answer is **Infective Endocarditis (IE)**. This condition involves an infection of the endocardial surface of the heart, typically the valves [1]. The clinical presentation is a triad of systemic infection, valvular destruction, and immunological/embolic phenomena [1]. * **Why it is correct:** **Fever** is the most common presenting symptom [2]. **Clubbing** is a classic sign of subacute IE (though less common in the antibiotic era) [1]. **Osler’s nodes** are painful, pea-sized, erythematous nodules found on the pads of fingers and toes; they are an **immunological phenomenon** caused by immune complex deposition in the skin [1]. **Analysis of Incorrect Options:** * **A. Typhoid Fever:** Characterized by "step-ladder" fever, bradycardia (Faget’s sign), and Rose spots. It does not cause clubbing or Osler’s nodes. * **B. Rheumatic Fever:** Presents with migratory polyarthritis, carditis, and subcutaneous nodules (painless, over bony prominences). While it involves the heart, Osler’s nodes are specific to IE [3]. * **C. Leptospirosis:** Typically presents with fever, conjunctival suffusion (redness without discharge), and calf tenderness. In severe cases (Weil’s disease), it involves jaundice and renal failure. **High-Yield Clinical Pearls for NEET-PG:** * **Duke’s Criteria:** Used for diagnosis. Major criteria include positive blood cultures and echocardiographic evidence of vegetation [4]. * **Peripheral Stigmata of IE:** * **Janeway Lesions:** Painless, hemorrhagic macules on palms/soles (Embolic). * **Roth Spots:** Retinal hemorrhages with pale centers (Immunological). * **Splinter Hemorrhages:** Linear streaks under the nails. * **Most common valve involved:** Mitral valve (except in IV drug users, where the **Tricuspid valve** is most common) [5]. * **Most common organism:** *Staphylococcus aureus* (Acute/IVDU) and *Viridans streptococci* (Subacute) [5].

Question 264: Which of the following diseases does not typically present as shock?

A. Meningococcemia
B. Erythema infectiosum (Correct Answer)
C. Toxic Shock Syndrome (TSS)
D. Staphylococcal Scalded Skin Syndrome (SSSS)

Explanation: ### Explanation The key to answering this question lies in distinguishing between systemic inflammatory conditions that lead to hemodynamic instability (shock) and benign, self-limiting viral exanthems. **Why Erythema Infectiosum is the correct answer:** Erythema infectiosum, also known as **Fifth Disease**, is caused by **Parvovirus B19**. It typically presents in children as a mild febrile illness followed by a characteristic "slapped-cheek" rash and a reticular (lace-like) pattern on the trunk and extremities. It is a benign condition and **does not cause shock**. Its primary complications are hematological (aplastic crisis in patients with chronic hemolytic anemias) rather than hemodynamic. **Analysis of incorrect options:** * **Meningococcemia:** Caused by *Neisseria meningitidis*, this can lead to **Waterhouse-Friderichsen syndrome** (adrenal hemorrhage) and profound septic shock due to severe endotoxemia and DIC. * **Toxic Shock Syndrome (TSS):** Defined by the clinical triad of fever, rash, and **hypotension (shock)**. It is mediated by superantigens (TSST-1 from *S. aureus* or pyrogenic exotoxins from *S. pyogenes*) that cause massive cytokine release. * **Staphylococcal Scalded Skin Syndrome (SSSS):** While primarily a toxin-mediated blistering disease (exfoliative toxins A and B), severe cases in neonates or infants can lead to massive fluid loss through denuded skin, resulting in **hypovolemic shock** and secondary sepsis. **NEET-PG High-Yield Pearls:** * **Parvovirus B19** targets **erythroid progenitor cells** (P-antigen). * In pregnancy, Parvovirus B19 can cause **Hydrops Fetalis** due to severe fetal anemia. * **TSS vs. SSSS:** TSS involves multi-organ failure and shock; SSSS involves superficial desquamation (Nikolsky sign positive) but can lead to shock via fluid loss. * **Meningococcemia** is the most common cause of rapidly progressive fatal septic shock in previously healthy young adults.

Question 265: Genital herpes is caused by which virus?

A. Herpes Simplex Virus type 1 (HSV-1)
B. Herpes Simplex Virus type 2 (HSV-2) (Correct Answer)
C. Varicella-Zoster Virus (VZV)
D. None of the above

Explanation: **Explanation:** Genital herpes is a common sexually transmitted infection (STI) characterized by painful, vesicular lesions in the genital and anal regions [1]. **1. Why Option B is Correct:** Historically and epidemiologically, **Herpes Simplex Virus type 2 (HSV-2)** is the primary cause of genital herpes [1]. It is almost exclusively transmitted via sexual contact. After the initial infection, the virus remains latent in the **sacral ganglia** (S2-S4) and can periodically reactivate, causing recurrent outbreaks [2]. **2. Why Other Options are Incorrect:** * **Option A (HSV-1):** While HSV-1 is the classic cause of orolabial herpes (cold sores) and resides in the **trigeminal ganglion**, it is increasingly becoming a common cause of *primary* genital herpes due to changing sexual practices (oral-genital contact) [1]. However, HSV-2 remains the "textbook" and most frequent cause of recurrent genital disease. * **Option C (VZV):** Varicella-Zoster Virus causes Chickenpox (primary infection) and Herpes Zoster/Shingles (reactivation). It does not cause genital herpes. **Clinical Pearls for NEET-PG:** * **Diagnosis:** The gold standard is Viral PCR (more sensitive than culture) [3]. * **Cytology:** **Tzanck Smear** shows characteristic **multinucleated giant cells** with Cowdry type A inclusion bodies (seen in HSV-1, HSV-2, and VZV). * **Treatment:** Acyclovir, Valacyclovir, or Famciclovir [4]. These drugs inhibit viral DNA polymerase but do not cure the latent infection. * **Neonatal Herpes:** Usually acquired during delivery through an infected birth canal; it is a serious condition often requiring Cesarean section if active lesions are present.

Question 266: Which of the following statements is NOT true about Legionnaire's pneumonia?

A. It is seen mainly in immunocompromised individuals.
B. Erythromycin is the drug of choice. (Correct Answer)
C. It is common in patients with hairy cell leukemia.
D. Smoking and alcohol are risk factors.

Explanation: The correct answer is **B**, as Erythromycin is no longer considered the drug of choice for Legionnaire’s disease. While macrolides were historically used, current clinical guidelines (IDSA/ATS) prioritize **Fluoroquinolones (e.g., Levofloxacin)** or newer macrolides like **Azithromycin** due to superior tissue penetration, better efficacy, and fewer gastrointestinal side effects. **Analysis of Options:** * **Option A:** Legionella is an opportunistic pathogen. While it can affect healthy individuals, it is significantly more prevalent and severe in **immunocompromised** patients, particularly those with impaired cell-mediated immunity. * **Option C:** There is a well-documented high-yield association between **Hairy Cell Leukemia** and *Legionella* infection. These patients are uniquely predisposed to this pathogen. * **Option D:** **Smoking, chronic lung disease (COPD), and alcohol consumption** are classic, major risk factors for acquiring Legionnaire's pneumonia [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Inhalation of aerosols from contaminated water sources (AC cooling towers, showers, nebulizers) [1]. No person-to-person spread. * **Clinical Clues:** Look for "Pneumonia + GI symptoms (Diarrhea)" or "Pneumonia + Neurological symptoms (Confusion)." * **Laboratory Hallmark:** **Hyponatremia** (low sodium) is a classic finding in Legionella cases. * **Diagnosis:** The **Urinary Antigen Test** is the most common rapid diagnostic method (detects Serogroup 1). Culture on **BCYE (Buffered Charcoal Yeast Extract) agar** is the gold standard. * **Microbiology:** It is a Gram-negative rod but stains poorly; **Silver stain (Dieterle)** is preferred.

Question 267: A young patient presented with fever (100 extdegree F), nausea, and vomiting. The patient also complained of vague abdominal discomfort. On general examination, icterus and hepatic tenderness were present. A family member had similar symptoms and was diagnosed with hepatitis E. Which of the following is the most likely route of transmission for the hepatitis E virus in this patient?

A. Skin contact
B. Fecal-oral route (Correct Answer)
C. Blood transfusion
D. Sexual contact

Explanation: ### Explanation **Correct Answer: B. Fecal-oral route** The clinical presentation of fever, icterus (jaundice), nausea, and hepatic tenderness in a young patient, combined with a family history of similar symptoms, strongly suggests **Hepatitis E Virus (HEV)** infection [2]. HEV is a non-enveloped RNA virus primarily transmitted via the **fecal-oral route**, most commonly through the consumption of contaminated drinking water. In developing countries, HEV is a major cause of epidemic and sporadic acute viral hepatitis. **Analysis of Options:** * **A. Skin contact:** HEV is not transmitted through casual skin-to-skin contact. * **C. Blood transfusion:** While rare instances of transfusion-associated HEV have been reported, it is not the primary or "most likely" route, especially in an outbreak or familial setting. * **D. Sexual contact:** Unlike Hepatitis B or C, sexual transmission of HEV is clinically insignificant and not a recognized primary mode of spread. **High-Yield Clinical Pearls for NEET-PG:** * **Epidemiology:** HEV is the most common cause of acute viral hepatitis worldwide. * **Pregnancy Warning:** HEV infection in pregnant women (especially during the 3rd trimester) is associated with a high risk of **Fulminant Hepatic Failure**, with mortality rates reaching up to **20-25%**. * **Zoonosis:** HEV genotypes 3 and 4 are zoonotic, often transmitted via undercooked pork or deer meat. * **Chronicity:** HEV usually causes acute self-limiting hepatitis, but it can cause **chronic hepatitis in immunocompromised patients** (e.g., organ transplant recipients). * **Serology:** Diagnosis is confirmed by detecting **IgM anti-HEV** antibodies [1].

Question 268: A 35-year-old male patient with a known case of HIV on Antiretroviral Therapy complains of fever, dyspnea, dry cough, and weight loss for the past 3 months. The chest X-ray of the patient is as below. What is your diagnosis?

A. Staphylococcal pneumonia
B. Pneumocystis pneumonia (Correct Answer)
C. Viral pneumonia
D. None of the above

Explanation: ***Pneumocystis pneumonia*** - **Bilateral perihilar ground-glass opacities** on chest X-ray along with **subacute presentation** of fever, dry cough, and dyspnea in an **HIV patient** is classic for **Pneumocystis jirovecii pneumonia (PCP)**. - Typically occurs when **CD4 count falls below 200 cells/μL** and presents with **gradual onset** over weeks to months with **weight loss** and **exertional dyspnea**. *Staphylococcal pneumonia* - Usually presents with **acute onset** and **productive cough** with **purulent sputum**, unlike the dry cough described. - Chest X-ray typically shows **lobar consolidation** or **cavitating lesions**, not bilateral ground-glass opacities. *Viral pneumonia* - Generally has a **more acute presentation** with **upper respiratory symptoms** like rhinorrhea and sore throat. - Chest X-ray shows **diffuse bilateral infiltrates** but lacks the characteristic **perihilar distribution** seen in PCP. *None of the above* - The clinical presentation and **bilateral perihilar ground-glass pattern** in an **immunocompromised HIV patient** is pathognomonic for PCP. - The **subacute timeline** of 3 months with **weight loss** further supports this diagnosis over other pneumonias.

Question 269: All the following are used in the treatment of Pneumocystis jirovecii pneumonia except?

A. Pentamidine
B. Dapsone
C. Cotrimoxazole
D. Fluoroquinolones (Correct Answer)

Explanation: Explanation: **Pneumocystis jirovecii pneumonia (PCP)** is a fungal infection primarily affecting immunocompromised patients, particularly those with HIV/AIDS (CD4 count <200 cells/µL) [1]. Despite being classified as a fungus, it does not respond to traditional antifungals like Ergosterol inhibitors. **Why Fluoroquinolones are the correct answer:** Fluoroquinolones (e.g., Levofloxacin, Ciprofloxacin) are DNA gyrase inhibitors used to treat bacterial infections. They have **no clinical activity** against *P. jirovecii*. Therefore, they are not used in the management of PCP. **Analysis of other options:** * **Cotrimoxazole (Trimethoprim-Sulfamethoxazole):** This is the **drug of choice** for both treatment and prophylaxis of PCP [1]. It acts by inhibiting the folic acid synthesis pathway of the organism. * **Pentamidine:** Used as an alternative for patients who are intolerant to or fail to respond to Cotrimoxazole. It is administered intravenously (for treatment) or via inhalation (for prophylaxis). * **Dapsone:** Often used in combination with Trimethoprim as a second-line treatment for mild-to-moderate PCP or as a prophylaxis agent in patients allergic to Sulfa drugs. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of Choice:** Cotrimoxazole (TMP-SMX) [1]. 2. **Steroid Indication:** Add Prednisone if $PaO_2 < 70$ mmHg or A-a gradient $> 35$ mmHg to prevent respiratory failure triggered by organism lysis [1]. 3. **Alternative regimens:** Clindamycin + Primaquine (highly effective for moderate disease) or Atovaquone. 4. **Diagnosis:** Silver stain (Gomori Methenamine Silver) showing "crushed ping-pong ball" appearance or Direct Fluorescent Antibody (DFA) testing. Induced sputum is the initial test; Bronchoalveolar lavage (BAL) is the gold standard [1].

Question 270: A 22-year-old male military recruit complains of a headache and stiff neck. He is examined, blood is drawn, and a lumbar puncture is performed. The glucose in the CSF is 100 mg/dL and the serum glucose is 120 mg/dL. The CSF shows 3 lymphocytes and 0 neutrophils/microliter. Which of the following conclusions concerning the interpretation of these findings is most accurate?

A. The CSF glucose level suggests bacterial meningitis
B. The CSF glucose level suggests viral meningitis
C. The lymphocytes suggest bacterial meningitis
D. There is no evidence for meningitis (Correct Answer)

Explanation: To arrive at the correct diagnosis, one must compare the patient’s Cerebrospinal Fluid (CSF) findings against the standard physiological ranges. [1] ### **Explanation of the Correct Answer** **Option D is correct** because the CSF parameters provided are within **normal limits**. 1. **CSF Glucose:** Normally, CSF glucose is approximately **60-70% of the serum glucose**. In this patient, the CSF glucose (100 mg/dL) is 83% of the serum glucose (120 mg/dL). This is normal; a low glucose (hypoglycorrhachia) would be required to suggest bacterial or fungal infection. [1] 2. **Cell Count:** Normal CSF contains **<5 WBCs/µL**, which are predominantly lymphocytes. This patient has only 3 lymphocytes and 0 neutrophils, which is a completely normal finding. [1] 3. **Conclusion:** Without pleocytosis (increased WBCs) or significant biochemical derangement, there is no evidence of meningitis, despite the clinical symptoms (which could be due to tension headache or viral prodrome). [2] ### **Why Other Options are Incorrect** * **Option A & B:** These are incorrect because the glucose level is **normal**. In bacterial meningitis, glucose is typically low (<40 mg/dL). In viral meningitis, glucose is usually normal, but the diagnosis still requires pleocytosis (increased WBCs), which is absent here. [1] * **Option C:** This is incorrect because 3 lymphocytes/µL is a **normal physiological finding** and does not indicate an inflammatory process. Bacterial meningitis is characterized by a marked **neutrophilic** pleocytosis. [1] ### **NEET-PG High-Yield Pearls** | Feature | Normal | Bacterial | Viral | TB/Fungal | | :--- | :--- | :--- | :--- | :--- | | **WBC Count** | < 5 | > 1000 (Neutrophils) | 10–500 (Lymphocytes) | 50–500 (Lymphocytes) | | **Glucose** | 60-70% of serum | **Low** (< 40) | Normal | **Low** | | **Protein** | < 45 mg/dL | **High** (> 250) | Mildly High | **Very High** | * **Clinical Pearl:** In military recruits, the most feared cause of meningitis is *Neisseria meningitidis*. However, always look at the **CSF/Serum Glucose ratio**; if it is >0.6, bacterial etiology is highly unlikely.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

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.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

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Sepsis and Septic Shock

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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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