Infectious Diseases — MCQs

A 46-year-old male, an IV drug abuser, presents to the OPD with complaints of fatigue, malaise, and rigors. His temperature was 38.5°C, pulse 84/min, BP 130/80 mm Hg. On cardiovascular examination, a pansystolic murmur was heard, loudest at the left sternal border. Three sets of blood cultures were taken consecutively. Transthoracic echocardiography (TTE) revealed vegetation on the tricuspid valve with tricuspid regurgitation. From the given history, which organism is most likely to be positive in blood cultures?

Q597Easy

Rose spots are seen in which of the following conditions?

Q598Easy

The clinical spectrum of Hansen's disease is best characterized by what?

Q599Easy

Which of the following antiviral drugs is NOT used in the management of chickenpox?

Q600Medium

A 22-year-old man with AIDS complains of persistent cough, night sweats, low-grade fever, and general malaise. A chest X-ray reveals an area of consolidation in the periphery of the left upper lobe, as well as hilar lymphadenopathy. Sputum cultures show acid-fast bacilli. Which of the following is the most likely diagnosis?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 591: Which of the following statements is NOT true in leptospirosis?

A. It is a zoonosis.
B. It can present with fever, petechiae, jaundice, and renal failure.
C. Doxycycline, penicillin, and macrolides are used in treatment.
D. It is diagnosed by phase contrast microscopy. (Correct Answer)

Explanation: **Leptospirosis** is a spirochetal infection caused by *Leptospira interrogans*. Understanding its diagnostic modalities and clinical presentation is high-yield for NEET-PG. **Why Option D is the Correct Answer (The False Statement):** While *Leptospira* are spirochetes, they are extremely thin (0.1 μm) and are **not** visible under standard light or phase-contrast microscopy. The gold standard for direct visualization is **Dark-field microscopy**. However, even dark-field has low sensitivity and specificity. In clinical practice, diagnosis is primarily confirmed via the **Microscopic Agglutination Test (MAT)**, ELISA (IgM), or PCR [1]. **Analysis of Other Options:** * **Option A (True):** It is a classic zoonosis [1]. Humans are accidental hosts, usually infected through contact with water or soil contaminated by the urine of infected animals (primarily rats) [1]. * **Option B (True):** This describes **Weil’s Disease**, the severe form of leptospirosis characterized by the triad of jaundice, renal failure, and hemorrhage (petechiae/purpura) [1]. * **Option C (True):** Antibiotics are effective. **Doxycycline** is the drug of choice for mild cases and for prophylaxis. **Penicillin G**, ceftriaxone, or macrolides (azithromycin) are used for severe or hospitalized cases. **High-Yield Clinical Pearls for NEET-PG:** * **Conjunctival Suffusion:** A pathognomonic sign (redness of eyes without inflammatory exudate). * **Biphasic Nature:** It typically presents in two phases: the septicemic phase followed by the immune phase (where meningitis may occur) [1]. * **CPK Levels:** Often elevated in leptospirosis, helping differentiate it from other tropical fevers like malaria or enteric fever. * **Prophylaxis:** Doxycycline (200 mg once weekly) is recommended for high-risk individuals (e.g., during floods).

Question 592: Which of the following is NOT a feature of primary tuberculosis?

A. Pleural effusion
B. Consolidation
C. Pulmonary fibrosis
D. None of the above (Correct Answer)

Explanation: **Explanation** Primary Tuberculosis (TB) occurs in an individual who has not been previously exposed to *Mycobacterium tuberculosis*. While often asymptomatic, it can present with several distinct radiological and clinical features [1]. **Why "None of the above" is correct:** All the listed options—Pleural effusion, Consolidation, and Pulmonary fibrosis—can indeed be features of primary TB. Therefore, none of them are "not" a feature. * **Consolidation (Option B):** This is the most common radiological finding in primary TB. Unlike post-primary TB (which favors the apices), primary TB consolidation typically involves the **middle and lower lobes**. * **Pleural Effusion (Option A):** This occurs in up to 25% of primary TB cases. It results from a hypersensitivity reaction to the mycobacterial antigens entering the pleural space rather than direct infection. * **Pulmonary Fibrosis (Option C):** While more characteristic of chronic or post-primary TB, primary TB heals by fibrosis and calcification [1]. The classic **Ghon complex** (parenchymal lesion + nodal involvement) eventually undergoes fibrosis and calcification to become a **Ranke complex** [1]. **High-Yield Clinical Pearls for NEET-PG:** 1. **Ghon Focus:** A subpleural area of granulomatous inflammation in the mid/lower lobes [1]. 2. **Ranke Complex:** A healed Ghon complex that has undergone calcification (visible on X-ray) [1]. 3. **Lymphadenopathy:** Hilar or paratracheal lymphadenopathy is a hallmark of primary TB in children, often causing extrinsic airway compression [2]. 4. **Epituberculosis:** A term used when a large area of collapse/consolidation occurs due to a lymph node compressing a bronchus in primary TB.

Question 593: Botulism is characterized by which of the following symptoms?

A. Seizure
B. Fever
C. Ascending paralysis
D. Descending symmetrical paralysis (Correct Answer)

Explanation: Botulism is caused by the neurotoxin produced by *Clostridium botulinum*. The toxin acts by irreversibly inhibiting the release of **acetylcholine** at the neuromuscular junction, leading to flaccid paralysis. [1] **1. Why Option D is Correct:** The hallmark of botulism is a **symmetric, descending flaccid paralysis**. It typically begins with cranial nerve involvement (the "4 Ds": Diplopia, Dysarthria, Dysphonia, and Dysphagia) and progresses downward to involve the upper extremities, trunk, and lower extremities. [1] Respiratory failure due to diaphragmatic paralysis is the most serious complication. [1] **2. Why Other Options are Incorrect:** * **A. Seizure:** Botulism toxin does not cross the blood-brain barrier; therefore, the central nervous system is spared. Patients remain mentally alert and do not experience seizures. [1] * **B. Fever:** Botulism is a toxin-mediated disease, not a systemic infection. Fever is typically absent unless a secondary complication (like aspiration pneumonia) occurs. * **C. Ascending paralysis:** This is characteristic of **Guillain-Barré Syndrome (GBS)**. In GBS, paralysis starts in the lower limbs and moves upward, whereas botulism moves downward. **High-Yield Clinical Pearls for NEET-PG:** * **Infant Botulism:** Associated with honey ingestion ("Floppy Baby Syndrome"). * **Foodborne Botulism:** Associated with home-canned foods or fermented fish. * **Diagnosis:** Primarily clinical; confirmed by identifying the toxin in serum, stool, or suspected food. [1] * **Treatment:** Immediate administration of **Equine Antitoxin** (for adults) or **Human Botulism Immune Globulin** (for infants). Do not wait for lab confirmation to start treatment. * **Autonomic signs:** Fixed, dilated pupils and dry mouth are common. [1]

Question 594: An asymptomatic adult with a CD4 count of 230/µL falls under which category of CDC classification?

A. A1
B. A2 (Correct Answer)
C. B2
D. C1

Explanation: The CDC classification for HIV/AIDS (1993) is a high-yield topic for NEET-PG. It uses a matrix based on **Clinical Categories (A, B, C)** and **CD4+ T-lymphocyte counts (1, 2, 3)**. ### 1. Why A2 is Correct * **Clinical Category A:** Includes asymptomatic HIV infection, persistent generalized lymphadenopathy (PGL), or acute (primary) HIV infection [1]. Since the patient is **asymptomatic**, they fall into Category A [1]. * **CD4 Category 2:** Defined as a CD4 count between **200–499/µL** [1]. * Combining these, an asymptomatic patient with a CD4 count of 230/µL is classified as **A2**. ### 2. Why Other Options are Incorrect * **A1:** Incorrect because Category 1 requires a CD4 count of **≥500/µL** [1]. * **B2:** Incorrect because Category B involves "Symptomatic, not A or C" conditions (e.g., Oral Candidiasis, Herpes Zoster, Bacillary Angiomatosis) [1]. This patient is asymptomatic. * **C1:** Incorrect because Category C is reserved for **AIDS-defining illnesses** (e.g., PCP pneumonia, Esophageal Candidiasis, Kaposi Sarcoma) regardless of CD4 count. Also, Category 1 implies a CD4 count ≥500/µL. ### 3. High-Yield Clinical Pearls * **The "AIDS" Threshold:** Any patient in Categories **A3, B3, or C1-C3** (i.e., CD4 <200/µL OR the presence of an AIDS-defining illness) is clinically diagnosed with AIDS. * **WHO vs. CDC:** While the CDC uses CD4 counts, the **WHO Staging System** (used more commonly in India/NACO guidelines) is primarily clinical (Stages 1–4) [1]. * **Prophylaxis Tip:** For any patient with CD4 <200/µL (Category 3), start **Cotrimoxazole** prophylaxis for *Pneumocystis jirovecii*.

Question 595: What is the most common extra-intestinal manifestation of amebiasis?

A. Amoebic liver abscess (Correct Answer)
B. Pleural effusion
C. Atelectasis
D. Cardiac tamponade

Explanation: **Amoebic Liver Abscess (ALA)** is the most common extra-intestinal manifestation of infection by *Entamoeba histolytica*. The parasite enters the portal circulation from the colon and travels to the liver, where it causes enzymatic necrosis of hepatocytes [1]. It is significantly more common in adult males (10:1 ratio) and typically presents as a solitary abscess in the **right lobe** of the liver. **Analysis of Options:** * **Amoebic Liver Abscess (Correct):** It occurs in approximately 1–10% of patients with invasive amebiasis. The classic "anchovy sauce" pus (reddish-brown, odorless) is a hallmark finding [1]. * **Pleural Effusion & Atelectasis (Incorrect):** These are secondary pulmonary complications. They usually occur due to sympathetic irritation of the diaphragm or direct rupture of a right-lobe liver abscess through the diaphragm into the pleural space. * **Cardiac Tamponade (Incorrect):** This is a rare but life-threatening complication caused by the rupture of an abscess located in the **left lobe** of the liver into the pericardial sac. **NEET-PG High-Yield Pearls:** 1. **Investigation of Choice:** Ultrasound is the initial screening tool, but **Contrast-Enhanced CT (CECT)** is more sensitive. 2. **Serology:** Enzyme-linked immunosorbent assay (ELISA) for antibodies is positive in >90% of cases. 3. **Treatment:** **Metronidazole** (or Tinidazole) is the drug of choice, followed by a luminal amebicide (e.g., Diloxanide furoate or Paromomycin) to eradicate the intestinal cyst carrier state. 4. **Aspiration Indications:** Only required if the abscess is large (>10cm), involves the left lobe (risk of rupture into pericardium), or fails to respond to medical therapy.

Question 596: A 46-year-old male, an IV drug abuser, presents to the OPD with complaints of fatigue, malaise, and rigors. His temperature was 38.5°C, pulse 84/min, BP 130/80 mm Hg. On cardiovascular examination, a pansystolic murmur was heard, loudest at the left sternal border. Three sets of blood cultures were taken consecutively. Transthoracic echocardiography (TTE) revealed vegetation on the tricuspid valve with tricuspid regurgitation. From the given history, which organism is most likely to be positive in blood cultures?

A. Streptococcus sanguis
B. Enterococcus faecium
C. Coxiella burnetii
D. Staphylococcus aureus (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Staphylococcus aureus** The patient presents with the classic triad of **IV drug abuse (IVDA)**, fever, and a pansystolic murmur at the left lower sternal border (indicative of **Tricuspid Regurgitation**). This clinical picture is diagnostic of **Right-sided Infective Endocarditis (IE)** [4]. In IV drug users, the skin is the primary source of entry for pathogens. **Staphylococcus aureus** is the most common causative organism (responsible for >60% of cases) in this population [3]. It typically presents acutely with high-grade fever and rapid valvular destruction. The tricuspid valve is involved in over 70% of IVDA-associated IE cases. **Analysis of Incorrect Options:** * **A. Streptococcus sanguis:** A member of the Viridans group streptococci, it is the most common cause of subacute IE following dental procedures, typically affecting previously damaged native valves (left-sided) [3]. * **B. Enterococcus faecium:** Often associated with IE following genitourinary or gastrointestinal manipulations, particularly in elderly patients or those with chronic prosthetic valve issues [3]. * **C. Coxiella burnetii:** The causative agent of Q fever [1]. It is a common cause of **culture-negative endocarditis** and usually presents as a chronic infection rather than an acute febrile illness. **Clinical Pearls for NEET-PG:** * **Most common valve in IVDA:** Tricuspid valve (Right-sided). * **Most common organism in IVDA:** *Staphylococcus aureus* [3]. * **Most common organism overall (Native Valve):** *Staphylococcus aureus* (previously Viridans Streptococci) [3]. * **Most common organism in Subacute IE:** *Streptococcus viridans*. * **Most common organism in Early Prosthetic Valve IE (<1 year):** *Staphylococcus epidermidis*. * **Diagnostic Gold Standard:** Duke’s Criteria (Major: Positive blood cultures and Echo evidence of vegetation) [2].

Question 597: Rose spots are seen in which of the following conditions?

A. Typhus fever
B. Typhoid fever
C. Enteric fever (Correct Answer)
D. Rheumatic fever

Explanation: **Explanation:** **Enteric Fever (Correct Answer):** Rose spots are a classic, pathognomonic cutaneous manifestation of **Enteric fever** (caused by *Salmonella Typhi* and *Paratyphi*). These are small (2–4 mm), blanching, erythematous maculopapules typically found on the upper abdomen and lower chest. They appear during the **second week** of illness and occur in approximately 30% of cases. The spots represent bacterial emboli in the dermis; notably, *Salmonella* can be cultured from these lesions. **Why other options are incorrect:** * **Typhoid fever:** While Typhoid fever is a subset of Enteric fever, "Enteric fever" is the more comprehensive and clinically accurate term in this context as it encompasses both *S. Typhi* and *S. Paratyphi* (both of which cause rose spots) [2]. * **Typhus fever:** Caused by *Rickettsia*, it presents with a maculopapular rash that starts in the axillae and spreads to the trunk, but these are not referred to as "rose spots" [1]. * **Rheumatic fever:** This condition is associated with **Erythema Marginatum**, which are pink, evanescent, non-pruritic rings with central clearing, primarily on the trunk and limbs. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** Rose spots appear in the 2nd week (the "Week of Complications") [2]. * **Step-ladder pyrexia:** The characteristic fever pattern of Enteric fever. * **Faget’s Sign:** Relative bradycardia (pulse does not rise proportionally with temperature), a key diagnostic clue. * **Diagnosis:** Use the **BASU** mnemonic for culture positivity: **B**lood (1st week), **A**ntibody/Widal (2nd week), **S**tool (3rd week), **U**rine (4th week). Bone marrow culture is the most sensitive overall.

Question 598: The clinical spectrum of Hansen's disease is best characterized by what?

A. Immunologic anergy
B. Chronic pneumonitis
C. Peripheral neuritis (Correct Answer)
D. Bacilli in lesions that digest tissues

Explanation: **Explanation:** Hansen’s disease (Leprosy), caused by *Mycobacterium leprae*, is primarily a disease of the **peripheral nerves** and skin [1]. The hallmark of its clinical spectrum is **peripheral neuritis**. *M. leprae* has a unique tropism for Schwann cells; the resulting nerve damage is caused by both direct bacterial invasion and the host’s cell-mediated immune response. This leads to characteristic sensory loss, motor weakness, and autonomic dysfunction, which are the primary causes of the deformities and disabilities associated with the disease [2]. **Analysis of Options:** * **A. Immunologic anergy:** While this occurs in the **Lepromatous (LL)** pole of the spectrum (specific anergy to *M. leprae* antigens), it does not characterize the *entire* spectrum. Tuberculoid (TT) patients exhibit a strong delayed-type hypersensitivity response [1]. * **B. Chronic pneumonitis:** Unlike *M. tuberculosis*, *M. leprae* is obligately intracellular and prefers cooler temperatures (30-33°C). It does not typically involve the lungs. * **D. Bacilli in lesions that digest tissues:** *M. leprae* does not produce exotoxins or lytic enzymes that "digest" tissue. Tissue destruction is secondary to trauma (due to anesthesia) or immune-mediated inflammation [2]. **High-Yield NEET-PG Pearls:** * **Cardinal Signs:** Hypopigmented patches with loss of sensation, thickened peripheral nerves, and positive skin smears [1]. * **Nerve Involvement:** The **Ulnar nerve** is the most commonly involved nerve in Leprosy. * **Ridley-Jopling Classification:** A five-group spectrum (TT, BT, BB, BL, LL) based on the host's immunological status [1]. * **First Sign:** The earliest clinical sign of Leprosy is often a **loss of temperature sensation** (cold before hot).

Question 599: Which of the following antiviral drugs is NOT used in the management of chickenpox?

A. Acyclovir
B. Famciclovir
C. Valacyclovir
D. Nevirapine (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Nevirapine** **1. Why Nevirapine is the Correct Answer:** Nevirapine is a **Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)** used exclusively in the treatment of **HIV-1 infection** [2]. It works by binding directly to the reverse transcriptase enzyme of the Human Immunodeficiency Virus. It has no inhibitory activity against DNA viruses like the Varicella-Zoster Virus (VZV), which causes chickenpox. **2. Why the Other Options are Incorrect:** * **A. Acyclovir:** This is the drug of choice for treating chickenpox, especially in adolescents, adults, and immunocompromised patients [1]. It is a nucleoside analog that inhibits viral DNA polymerase [2]. * **B. Famciclovir:** This is a prodrug of penciclovir [2]. It has a longer half-life than acyclovir and is effective against VZV [1]. It is frequently used for herpes zoster but is also an acceptable alternative for varicella. * **C. Valacyclovir:** This is the L-valyl ester prodrug of acyclovir [2]. It has superior oral bioavailability compared to acyclovir and is commonly used in the management of VZV infections to reduce the severity and duration of symptoms [1]. **3. Clinical Pearls for NEET-PG:** * **Drug of Choice:** Oral Acyclovir is the standard for healthy patients >12 years old; **IV Acyclovir** is mandatory for disseminated disease or varicella pneumonia [1]. * **Mechanism of Action:** Acyclovir requires initial phosphorylation by **viral thymidine kinase** to become active (Acyclovir monophosphate) [2]. * **Contraindication:** Aspirin should be avoided in children with chickenpox due to the risk of **Reye’s Syndrome**. * **Post-exposure Prophylaxis:** Varicella-Zoster Immunoglobulin (VZIG) is indicated for exposed susceptible individuals at high risk (e.g., pregnant women, neonates, immunocompromised).

Question 600: A 22-year-old man with AIDS complains of persistent cough, night sweats, low-grade fever, and general malaise. A chest X-ray reveals an area of consolidation in the periphery of the left upper lobe, as well as hilar lymphadenopathy. Sputum cultures show acid-fast bacilli. Which of the following is the most likely diagnosis?

A. Bronchopneumonia
B. Pulmonary abscess
C. Sarcoidosis
D. Tuberculosis (Correct Answer)

Explanation: **Explanation:** The clinical presentation of persistent cough, night sweats, low-grade fever, and malaise in a patient with AIDS is highly suggestive of an opportunistic infection, most notably **Tuberculosis (TB)** [1]. 1. **Why Tuberculosis is correct:** The presence of **Acid-Fast Bacilli (AFB)** in sputum cultures is the diagnostic hallmark of *Mycobacterium tuberculosis* [2]. In HIV-infected individuals with relatively preserved CD4 counts, TB often presents with classic upper lobe infiltrates. However, as immunosuppression progresses, atypical presentations like **hilar lymphadenopathy** and lower/middle lobe consolidation (resembling primary TB) become more common [1]. The combination of constitutional symptoms, radiological findings, and positive AFB staining confirms the diagnosis [2][4]. 2. **Why other options are incorrect:** * **Bronchopneumonia:** While it causes consolidation, it typically presents with acute high-grade fever and purulent sputum; it would not show acid-fast bacilli on culture. * **Pulmonary abscess:** Characterized by a thick-walled cavity with an air-fluid level on X-ray, usually caused by anaerobes or *S. aureus*, not AFB. * **Sarcoidosis:** Can cause hilar lymphadenopathy, but it is a non-infectious granulomatous disease. It would not present with AFB in sputum and is less likely in an immunocompromised patient presenting with classic infectious constitutional symptoms. **NEET-PG High-Yield Pearls:** * **HIV-TB Co-infection:** TB is the most common opportunistic infection in HIV patients in India [1]. * **Radiology:** In advanced AIDS (low CD4), TB often lacks cavitation and presents with mediastinal lymphadenopathy or miliary patterns [1][3]. * **Diagnosis:** Sputum smear microscopy (Ziehl-Neelsen stain) and **CBNAAT (GeneXpert)** are the initial investigations of choice. CBNAAT is preferred as it also detects Rifampicin resistance. [4] A primary TB complex, or Ranke complex, classically involves a periphery lung lesion (Ghon focus) and hilar lymph node involvement.

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Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

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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.)

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Healthcare-Associated Infections

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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