Infectious Diseases Practice Questions

Q: What is the most common causative organism causing lobar pneumonia?

Streptococcus pneumonia. **Explanation:** **Streptococcus pneumoniae** (Pneumococcus) remains the most common cause of community-acquired pneumonia (CAP) [1] and the classic cause of **lobar pneumonia**. The underlying medical concept involves its virulence factor, the polysaccharide capsule, which allows it to evade phagocytosis and spread rapidly through the Pores of Kohn, leading to uniform consolidation of an entire lobe. **Analysis of Options:** * **Streptococcus pneumoniae (Correct):** It is responsible for nearly 60-80% of bacterial lobar pneumonia cases. It typically presents with sudden onset chills, fever, and "rusty" sputum [1]. * **Staphylococcus aureus:** More commonly associated with **bronchopneumonia** (patchy distribution) rather than lobar. It often occurs post-influenza and is notorious for causing complications like lung abscesses and pneumatoceles [1]. * **Streptococcus pyogenes:** A rare cause of pneumonia; it more frequently causes pharyngitis, skin infections, or necrotizing fasciitis. When it does cause pneumonia, it is often severe with rapid pleural effusion. * **Hemophilus influenzae:** A common cause of CAP, especially in patients with underlying **COPD** [1] or cystic fibrosis, but it typically presents as bronchopneumonia rather than classic lobar consolidation. **High-Yield Clinical Pearls for NEET-PG:** 1. **Stages of Lobar Pneumonia:** Congestion → Red Hepatization (RBCs/fibrin) → Gray Hepatization (WBCs/fibrin) → Resolution. 2. **Sputum Color:** *S. pneumoniae* (Rusty) [1], *Klebsiella* (Currant jelly), *S. aureus* (Purulent/Golden). 3. **Radiology:** A "silhouette sign" on X-ray helps localize the affected lobe (e.g., loss of right heart border in right middle lobe pneumonia). 4. **Vaccination:** The PCV13 and PPSV23 vaccines are crucial for preventing invasive pneumococcal disease in elderly and immunocompromised patients.

Q: A 57-year-old male is admitted to the hospital for a suspected kidney infection (likely pyelonephritis). The patient is placed on intravenous antibiotic therapy but continues to have a temperature of 103°F after 3 days of therapy. The urine culture grows lactose-fermenting Gram-negative bacilli which are pan drug-sensitive. On examination, he appears ill and has marked left flank tenderness. Ultrasound depicts a specific finding. What is the most likely diagnosis?

Perinephric abscess. ***Perinephric abscess*** - **Persistent high fever** despite 3 days of appropriate antibiotic therapy in pyelonephritis strongly suggests **abscess formation**, as antibiotics cannot penetrate well into enclosed collections. - Ultrasound would show a **hypoechoic fluid collection** in the **perinephric space** surrounding the kidney, which is the key diagnostic finding. *Hydronephrosis* - Would present with **obstructive symptoms** and **dilated renal pelvis** on ultrasound, not persistent fever after antibiotic treatment. - Usually associated with **decreased urine output** and **relief of pain** with positioning, unlike this case. *Nephrolithiasis* - Typically presents with **colicky pain** that radiates to the groin, not constant flank tenderness. - Ultrasound would show **echogenic stones** with **acoustic shadowing**, and fever would resolve with antibiotics if infection was present. *Emphysematous pyelonephritis* - Occurs primarily in **diabetic patients** and involves **gas-forming bacteria** creating emphysema in renal parenchyma. - Ultrasound would show **hyperechoic foci** with **dirty shadowing** from gas, and the organism is typically **Klebsiella** or **E. coli**, not just any lactose-fermenter.

Q: Which one of the following is not a feature of leptospirosis?

Hepatorenal syndrome. **Explanation:** Leptospirosis, caused by the spirochete *Leptospira interrogans*, is a zoonotic infection characterized by a wide spectrum of clinical manifestations. The severe form, known as **Weil’s Disease**, is defined by the triad of jaundice, acute kidney injury (AKI), and hemorrhage. **Why Hepatorenal Syndrome (C) is the Correct Answer:** In leptospirosis, renal failure is primarily caused by **acute tubular necrosis (ATN)** or **interstitial nephritis** due to direct bacterial invasion and toxin-mediated damage. **Hepatorenal Syndrome (HRS)**, however, is a specific functional renal failure occurring in the setting of advanced cirrhosis or portal hypertension due to splanchnic vasodilation [1]. While leptospirosis involves both the liver and kidneys, the pathophysiology is direct organ damage, not the hemodynamic shifts characteristic of HRS. **Analysis of Incorrect Options:** * **A. Aminotransferase elevation (<5 times):** Characteristically, leptospirosis causes significant jaundice (high bilirubin) but only mild-to-moderate elevations in ALT/AST (usually <500 U/L). This "bilirubin-enzyme dissociation" helps distinguish it from viral hepatitis. * **B. Elevated Creatinine Phosphokinase (CPK):** Muscle tenderness and elevated CPK are hallmark features of the septicemic phase, reflecting myositis. This is a high-yield diagnostic clue. * **D. Thrombocytopenia:** Common in severe cases, it contributes to the hemorrhagic manifestations (petechiae, epistaxis, or pulmonary hemorrhage) seen in Weil’s disease. **NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** Microscopic Agglutination Test (MAT). * **Renal Feature:** Unlike most causes of AKI, leptospirosis often presents with **hypokalemia** (due to proximal tubular dysfunction). * **Drug of Choice:** Doxycycline (mild); Penicillin G (severe). * **Classic Sign:** Conjunctival suffusion (redness without inflammatory exudate).

Q: A 32-year-old male who recently visited a sea coast presented with an ulcer over the left leg. What is the probable causative organism?

Vibrio vulnificus. **Explanation:** The clinical presentation of a skin ulcer following exposure to seawater or coastal environments is a classic "high-yield" scenario pointing toward **Vibrio vulnificus**. **Why Vibrio vulnificus is correct:** *Vibrio vulnificus* is a gram-negative, halophilic (salt-loving) bacterium found in warm coastal waters. Infection typically occurs via two routes: ingestion of contaminated seafood (leading to septicemia) or **wound exposure to seawater**. It can cause aggressive soft tissue infections ranging from cellulitis and ulcers to life-threatening necrotizing fasciitis. Patients with underlying liver disease or iron overload are at particularly high risk for severe systemic dissemination. **Why other options are incorrect:** * **Pasteurella multocida:** Associated with animal bites or scratches, most commonly from **cats or dogs**, not seawater. * **Micrococcus halophillus:** While halophilic, this organism is generally considered non-pathogenic to humans and is not a recognized cause of marine-acquired leg ulcers. * **Neisseria gonorrhea:** Causes sexually transmitted infections. While it can cause disseminated gonococcal infection (DGI) with skin lesions (typically hemorrhagic papules or pustules), it is not associated with coastal exposure. **Clinical Pearls for NEET-PG:** * **Key Association:** Seawater exposure + Rapidly progressing skin lesion = *Vibrio vulnificus*. * **Risk Factor:** Chronic liver disease (Cirrhosis) or Hemochromatosis increases mortality risk significantly due to the organism's requirement for iron. * **Treatment:** The drug of choice is typically a combination of **Doxycycline and a third-generation Cephalosporin** (e.g., Ceftriaxone). * **Differential Diagnosis:** *Mycobacterium marinum* also causes "fish tank granuloma" after water exposure, but it presents as a chronic, indolent "sporotrichoid" nodules rather than an acute ulcer.

Q: What does I.R.L.S. stand for?

Immune reconstitution inflammatory syndrome. **Explanation:** **Immune Reconstitution Inflammatory Syndrome (IRIS)** [1] is a clinical condition observed in HIV-infected patients where the immune system begins to recover after starting **Antiretroviral Therapy (ART)**, but then responds to a previously acquired opportunistic infection with an overwhelming inflammatory response. **1. Why Option C is Correct:** The term accurately reflects the pathophysiology: * **Immune Reconstitution:** The recovery of CD4+ T-cell counts and immune function following ART [1]. * **Inflammatory:** The clinical symptoms are caused by an exaggerated, "paradoxical" inflammatory response [1]. * **Syndrome:** A collection of signs/symptoms resulting from this immune flare. **2. Why Other Options are Incorrect:** * **Option A & B:** While "Idiopathic" or "Immunological" might sound plausible, they are not the standard medical nomenclature. The hallmark of the condition is the **inflammatory** damage to tissues. * **Option D:** This is a distractor that rearranges the words. The sequence must follow the physiological process: first the immune system reconstitutes, then the inflammation occurs. **Clinical Pearls for NEET-PG:** * **Pathogens:** Most commonly associated with *Mycobacterium tuberculosis*, *Cryptococcus neoformans*, and CMV. * **Two Types:** 1. **Paradoxical IRIS:** Worsening of a known infection already under treatment [1]. 2. **Unmasking IRIS:** Appearance of a previously undiagnosed (occult) infection [1]. * **Risk Factors:** Low baseline CD4 count (<50 cells/µL) and a rapid drop in viral load after starting ART [1]. * **Management:** Usually, ART is continued. Mild cases are treated with NSAIDs; severe cases (especially CNS involvement) require corticosteroids.

Q: What is the drug of choice for the condition shown in the endoscopic view?

Fluconazole. ***Fluconazole*** - **Systemic antifungal** with excellent **oral bioavailability** and **tissue penetration**, making it ideal for esophageal candidiasis treatment. - **First-line therapy** for esophageal candidiasis due to its efficacy against **Candida albicans** and good tolerability profile. *Ketoconazole* - Associated with significant **hepatotoxicity** and **drug interactions** due to CYP450 inhibition, making it less preferred. - **Poor oral absorption** requires acidic environment and has **variable bioavailability** compared to fluconazole. *Clotrimazole* - **Topical antifungal** with limited systemic absorption, inadequate for treating **deep esophageal infection**. - Primarily used for **superficial mucocutaneous** candidiasis, not effective for esophageal involvement. *Nystatin* - **Not absorbed** from the gastrointestinal tract, providing only **local action** insufficient for esophageal candidiasis. - Reserved for **oral thrush** and superficial candidal infections, lacks systemic penetration needed for esophageal disease.

Q: Secondary pulmonary tuberculosis usually involves which part of the lungs?

Apex of lungs. **Explanation:** The correct answer is **B. Apex of lungs**. **1. Why the Apex is the Primary Site:** Secondary (reactivation) tuberculosis occurs in individuals who have been previously sensitized to *Mycobacterium tuberculosis* [1]. The organism is an **obligate aerobe**, meaning it thrives in environments with high oxygen tension. In an upright human, the apex of the lung has the highest **ventilation-perfusion (V/Q) ratio** [2]. Due to lower hydrostatic pressure at the top of the lungs, blood flow is significantly reduced compared to ventilation, resulting in the highest alveolar oxygen concentration ($P_AO_2$) in the body. This oxygen-rich environment provides the ideal milieu for the mycobacteria to proliferate. **2. Analysis of Incorrect Options:** * **A, C, and D (Base, Middle, and Lower Lobes):** These areas have higher blood flow but lower V/Q ratios and lower oxygen tension compared to the apices. While **Primary TB** often involves the lower or middle lobes (Ghon complex) [1] due to higher ventilation volume, **Secondary TB** specifically targets the apices (Simon’s foci). **3. Clinical Pearls for NEET-PG:** * **Location:** Secondary TB typically involves the **apical and posterior segments** of the upper lobes or the superior segment of the lower lobes [3]. * **Pathology:** Unlike primary TB, secondary TB is characterized by **cavitation** [3] due to a brisk delayed-type hypersensitivity (Type IV) response, which leads to tissue necrosis. * **Radiology:** Look for "cavitary lesions" in the infraclavicular or apical regions on a chest X-ray. * **Mnemonic:** "Secondary = Superior" (Upper lobes/Apex).

Question 1

What is the most common causative organism causing lobar pneumonia?

Accepted Answer

Streptococcus pneumonia

Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Hemophilus influenza

Question 2

A 57-year-old male is admitted to the hospital for a suspected kidney infection (likely pyelonephritis). The patient is placed on intravenous antibiotic therapy but continues to have a temperature of 103°F after 3 days of therapy. The urine culture grows lactose-fermenting Gram-negative bacilli which are pan drug-sensitive. On examination, he appears ill and has marked left flank tenderness. Ultrasound depicts a specific finding. What is the most likely diagnosis?

Accepted Answer

Perinephric abscess

Answer

Hydronephrosis

Answer

Nephrolithiasis

Answer

Emphysematous pyelonephritis

Question 3

Which one of the following is not a feature of leptospirosis?

Accepted Answer

Hepatorenal syndrome

Answer

Aminotransferase elevation to less than five times

Answer

Elevated creatinine phosphokinase

Answer

Thrombocytopenia

Question 4

A 40-year-old HIV-positive lady presented with multiple, discrete, firm lymphadenopathy in the posterior cervical and supraclavicular regions of 6 months duration. She also complained of chronic cough during this period. A surgical biopsy of the lymph nodes was diagnosed as TB lymphadenitis. Which statement is true in this setting?

Accepted Answer

Higher bacteriological yield from microscopy and culture is expected.

Answer

Granulomas in the lymph node biopsy specimen will be more numerous in this patient.

Answer

An important differential diagnosis is Kikuchi's disease.

Answer

Systemic symptoms are uncommon in HIV-infected persons due to associated pulmonary disease.

Question 5

Which of the following statements regarding cysticercosis is FALSE?

Accepted Answer

Commonest sites are meninges and cerebral ventricles.

Answer

Calcification is common.

Answer

It causes focal neurological complications.

Answer

It is found in subcutaneous tissues.

Question 6

A 32-year-old male who recently visited a sea coast presented with an ulcer over the left leg. What is the probable causative organism?

Accepted Answer

Vibrio vulnificus

Answer

Pasteurella multocida

Answer

Micrococcus halophillus

Answer

Neisseria gonorrhea

Question 7

What is the most common disease caused by Cytomegalovirus (CMV) in post bone-marrow transplant patients?

Accepted Answer

Pneumonia

Answer

Pyelonephritis

Answer

Meningitis

Answer

Gastrointestinal ulceration

Question 8

What does I.R.L.S. stand for?

Accepted Answer

Immune reconstitution inflammatory syndrome

Answer

Immune reconstitution idiopathic syndrome

Answer

Immune reconstitution immunological syndrome

Answer

Inflammatory reconstitution immune syndrome

Question 9

What is the drug of choice for the condition shown in the endoscopic view?

Accepted Answer

Fluconazole

Answer

Ketoconazole

Answer

Clotrimazole

Answer

Nystatin

Question 10

Secondary pulmonary tuberculosis usually involves which part of the lungs?

Accepted Answer

Apex of lungs

Answer

Base of lungs

Answer

Middle lobes

Answer

Lower lobes

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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