Infectious Diseases Practice Questions

Q: Acute viral hepatitis is diagnosed by?

Variable increase in transaminase level. **Explanation:** In acute viral hepatitis, the hallmark of diagnosis is the biochemical evidence of hepatocellular necrosis [1]. **Why Option B is correct:** The characteristic feature of acute viral hepatitis is a **variable but significant increase in serum transaminases** (ALT and AST) [1]. These enzymes are released into the bloodstream following hepatocyte injury. In acute cases, these levels typically rise above 500 U/L and often exceed 1000 U/L [3]. The increase is "variable" because the peak level depends on the timing of the blood draw relative to the onset of symptoms and the severity of the viral insult. **Analysis of Incorrect Options:** * **Option A:** While hepatic injury is related to transaminase levels, the term "variable increase" more accurately describes the clinical presentation where levels fluctuate during the prodromal and icteric phases. * **Option C:** **IgG** anti-HAV indicates past infection or immunity (vaccination). For the diagnosis of *acute* Hepatitis A, **IgM** anti-HAV is the specific marker required. * **Option D:** This is factually incorrect. Transaminases are the most sensitive indicators of acute liver cell injury; a "no rise" scenario would rule out acute hepatitis. **High-Yield Clinical Pearls for NEET-PG:** * **ALT vs. AST:** In viral hepatitis, **ALT is typically higher than AST** (ALT > AST). This is the opposite of Alcoholic Hepatitis, where AST:ALT is > 2:1. * **Decline of Enzymes:** A rapid fall in transaminases accompanied by a rising Prothrombin Time (PT/INR) and increasing bilirubin is a grave sign indicating **fulminant hepatic failure** (massive hepatocyte loss) [2]. * **Gold Standard for Acute Diagnosis:** Serology (e.g., HBsAg, IgM anti-HBc for Hep B; IgM anti-HAV for Hep A) is used to identify the specific viral etiology [4].

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: Stage III of Lyme's disease is characterized by what?

Arthritis. **Explanation:** Lyme disease, caused by the spirochete *Borrelia burgdorferi* (transmitted by the *Ixodes* tick), progresses through three distinct clinical stages [1]. Understanding the chronicity of symptoms is key to distinguishing these stages. **1. Why Arthritis is Correct:** **Stage III (Late Disseminated Infection)** occurs months to years after the initial tick bite. Its hallmark manifestation is **chronic large-joint arthritis**, most commonly affecting the **knee** [1]. Other Stage III features include acrodermatitis chronica atrophicans (skin atrophy) and subtle encephalopathy. The arthritis is typically episodic or persistent and results from an immune-mediated response to the persistent spirochetes [1]. **2. Why Other Options are Incorrect:** * **Meningoencephalitis & Myocarditis:** These are classic features of **Stage II (Early Disseminated Infection)**, which occurs weeks to months after the bite. Stage II is characterized by the "triad" of cranial nerve palsies (especially bilateral Bell’s palsy), meningitis/radiculoneuropathy, and AV nodal blocks (myocarditis). * **Nephritis:** This is not a standard clinical feature of Lyme disease in humans (though "Lyme nephritis" is a recognized entity in veterinary medicine, specifically dogs). **3. NEET-PG High-Yield Pearls:** * **Stage I (Early Localized):** Characterized by **Erythema Chronicum Migrans** (target/bull’s eye rash) and flu-like symptoms [1]. * **Drug of Choice:** **Doxycycline** is the first-line treatment for early stages [1]. * **Neurological/Cardiac involvement:** Treated with IV **Ceftriaxone** [1]. * **Vector:** *Ixodes scapularis* (Deer tick); the same tick transmits Babesiosis and Anaplasmosis (co-infections) [1]. * **Prophylaxis:** A single dose of Doxycycline (200mg) if the tick was attached for >36 hours.

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: What is the recommended post-exposure prophylaxis for HIV?

Tenofovir + Lamivudine for 4 weeks. **Explanation:** The current standard of care for HIV Post-Exposure Prophylaxis (PEP) has shifted towards simplified, highly effective regimens with better safety profiles. According to the latest **NACO (National AIDS Control Organization) and WHO guidelines**, the preferred regimen for PEP is a combination of two or three antiretroviral drugs for a duration of **28 days (4 weeks)**. **1. Why Option A is correct:** The combination of **Tenofovir (TDF) 300 mg + Lamivudine (3TC) 300 mg** (or Emtricitabine) is the backbone of PEP. In many updated protocols, a third drug—an Integrase Inhibitor like **Dolutegravir (DTG)**—is added (TDF + 3TC + DTG). However, in the context of standard MCQ options based on basic NACO dual-therapy recommendations, Tenofovir + Lamivudine for 4 weeks is the most appropriate choice. **2. Why the other options are incorrect:** * **Option B:** Ritonavir is a protease inhibitor used as a "booster" for other drugs (like Lopinavir); it is not used as a primary dual-therapy backbone with Lamivudine. * **Option C:** This was an older "expanded regimen" (Zidovudine + Lamivudine + Indinavir). Indinavir is rarely used now due to significant side effects like nephrolithiasis. * **Option D:** A single dose is insufficient to prevent viral replication and integration into the host genome. PEP must be continued for the full 28-day course. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** PEP should be initiated as soon as possible, ideally within **2 hours**, and no later than **72 hours** after exposure. * **Duration:** Always **28 days**. * **Baseline Testing:** Perform HIV testing at baseline, 6 weeks, 12 weeks, and 6 months post-exposure. * **Preferred Triple Regimen (Latest):** TDF (300mg) + 3TC (300mg) + DTG (50mg) once daily.

Question 1

Acute viral hepatitis is diagnosed by?

Accepted Answer

Variable increase in transaminase level

Answer

Hepatic injury related with transaminase level

Answer

IgG anti-HAV used for diagnosis

Answer

No rise of transaminase at all

Question 2

A 48-year-old HIV-positive male presents with 3 weeks of cough, fever, night sweats, weight loss, and diarrhea. He is not taking any treatment for HIV and has a CD4 count of <50. What is the most likely diagnosis?

Accepted Answer

Mycobacterium avium complex

Answer

Cytomegalovirus

Answer

Candidiasis

Answer

Pneumocystis jiroveci

Question 3

A patient presents with high fever, signs of raised intracranial pressure, and a history of chronic otitis media. What is the most likely diagnosis?

Accepted Answer

Brain abscess

Answer

Pyogenic meningitis

Answer

Acute subarachnoid hemorrhage

Answer

Acute osteomyelitis of skull bone

Question 4

In an HIV-positive patient with tuberculosis, all are true except?

Accepted Answer

Increased sputum positivity for AFB

Answer

Decreased cavitation in the lungs

Answer

Highly variable tuberculin tests

Answer

Decreased fibrosis

Question 5

What is the most common causative organism causing lobar pneumonia?

Accepted Answer

Streptococcus pneumonia

Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Hemophilus influenza

Question 6

Stage III of Lyme's disease is characterized by what?

Accepted Answer

Arthritis

Answer

Meningoencephalitis

Answer

Myocarditis

Answer

Nephritis

Question 7

Which of the following is the optimum treatment in a patient with chronic hepatitis B and elevated serum AST levels?

Accepted Answer

Lamivudine

Answer

Lamivudine and interferons

Answer

Immunoglobulins

Answer

Interferons

Question 8

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 9

What is the recommended post-exposure prophylaxis for HIV?

Accepted Answer

Tenofovir + Lamivudine for 4 weeks

Answer

Lamivudine + Ritonavir for 4 weeks

Answer

Zidovudine + Lamivudine + Indinavir for 4 weeks

Answer

Single dose Zidovudine + Lamivudine + Indinavir

Question 10

Which of the following is NOT a predisposing factor for Pneumococcal Pneumonia?

Accepted Answer

Thalassemia

Answer

Chronic renal failure (CRF)

Answer

Lymphoma

Answer

Old age

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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