Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 411: Which of the following characterizes amebic liver disease?

A. Most common in the right lobe of the liver (Correct Answer)
B. Diarrhea is the most common presentation
C. Resistant to metronidazole
D. The liver is the most common primary site of infection

Explanation: **Explanation:** Amebic liver abscess (ALA) is the most common extra-intestinal manifestation of infection by *Entamoeba histolytica*. **Why Option A is Correct:** The **right lobe of the liver** is involved in approximately 70–80% of cases. This predilection occurs because the right lobe receives the bulk of the venous drainage from the superior mesenteric vein (which drains the cecum and ascending colon, the primary sites of intestinal amebiasis) via a "streaming" effect in the portal circulation. **Why the Other Options are Incorrect:** * **Option B:** While ALA is a complication of intestinal amebiasis, **fever and right upper quadrant pain** are the most common presentations. Diarrhea is present in less than one-third of patients at the time of diagnosis [1]. * **Option C:** ALA is highly sensitive to nitroimidazoles. **Metronidazole** (or Tinidazole) remains the drug of choice [2], followed by a luminal amebicide (like Paromomycin) to eradicate the intestinal cyst stage. * **Option D:** The **colon** (large intestine) is the primary site of infection [1]. The liver is the most common *extra-intestinal* site, reached via the portal venous system. **NEET-PG High-Yield Pearls:** * **Demographics:** Most common in adult males (10:1 ratio), often associated with chronic alcohol consumption. * **Aspirate:** Classically described as **"Anchovy sauce"** appearance (odorless, reddish-brown, consisting of necrotic hepatocytes) [1]. * **Imaging:** Usually presents as a solitary abscess. * **Diagnosis:** Serology (ELISA) is highly sensitive; ultrasound is the initial imaging of choice. * **Treatment:** Medical management is successful in >90% of cases; needle aspiration is only indicated if the abscess is large (>10cm), at risk of rupture (left lobe), or fails to respond to antibiotics [2].

Question 412: Which of the following statements regarding amebic dysentery is true?

A. The incubation period is typically 7-10 days.
B. It is characterized by profuse, watery diarrhea.
C. The diagnostic mucosal lesion is most commonly found in the rectum.
D. Diagnostic mucosal findings are typically observed on sigmoidoscopy. (Correct Answer)

Explanation: **Explanation:** Amebic dysentery, caused by the protozoan *Entamoeba histolytica*, primarily involves the large intestine. [1] **Why Option D is correct:** Sigmoidoscopy is a vital diagnostic tool because it allows direct visualization of the colonic mucosa. In amebic dysentery, the characteristic **"flask-shaped ulcers"** (narrow neck and broad base) are often visible. Scrapings from the base of these ulcers can be examined microscopically for motile trophozoites containing ingested RBCs, which is pathognomonic. **Analysis of Incorrect Options:** * **Option A:** The incubation period is highly variable, typically ranging from **2 to 4 weeks**, though it can extend from a few days to several months. [1] 7-10 days is too short for a typical presentation. * **Option B:** Amebic dysentery is characterized by **bloody mucoid stools** (small volume) rather than profuse watery diarrhea. [1] Profuse watery diarrhea is more characteristic of secretory processes like Cholera or ETEC. * **Option C:** While the rectum can be involved, the **cecum and ascending colon** are the most common sites for amebic lesions due to fecal stasis, which allows the parasite more time to invade the mucosa. **NEET-PG High-Yield Pearls:** * **Pathognomonic finding:** Trophozoites with **ingested RBCs** (Erythrophagocytosis). * **Morphology:** Flask-shaped ulcers that do not typically penetrate the muscularis layer (unless perforation occurs). * **Complication:** The most common extra-intestinal manifestation is an **Amebic Liver Abscess** (usually in the right lobe; "anchovy sauce" pus). [1] * **Treatment:** Oral Nitroimidazoles (Metronidazole/Tinidazole) followed by a luminal amebicide (Paromomycin or Diloxanide furoate) to eradicate cysts.

Question 413: Flu-like symptoms followed by radiographic evidence of lung consolidation in a non-smoker is most commonly due to:

A. Klebsiella pneumoniae
B. Staphylococcus aureus (Correct Answer)
C. Streptococcus pneumoniae
D. Pseudomonas aeruginosa

Explanation: The clinical presentation of "flu-like symptoms" followed by rapid development of lung consolidation (lobar or necrotizing pneumonia) is a classic description of **Post-Viral Secondary Bacterial Pneumonia** [1]. **Why Staphylococcus aureus is correct:** While *Streptococcus pneumoniae* is the most common cause of community-acquired pneumonia (CAP) overall, **Staphylococcus aureus** (including MRSA) is the most characteristic and feared pathogen following an Influenza infection [1]. The virus damages the respiratory epithelium and impairs ciliary clearance, allowing *S. aureus* to invade. It typically presents as a severe, necrotizing pneumonia with a high tendency for cavitation and abscess formation, even in previously healthy non-smokers. **Analysis of Incorrect Options:** * **Streptococcus pneumoniae (C):** Although it remains a common cause of post-viral pneumonia, the NEET-PG pattern specifically highlights *S. aureus* when the question emphasizes the transition from "flu-like symptoms" to severe consolidation/complications [1]. * **Klebsiella pneumoniae (A):** Classically associated with chronic alcoholics and diabetics [1]. It presents with "currant jelly sputum" and bulging fissures on X-ray, rather than a post-viral prodrome. * **Pseudomonas aeruginosa (D):** Primarily seen in patients with structural lung disease (Cystic Fibrosis, Bronchiectasis) or those who are immunocompromised/ventilated. **High-Yield Clinical Pearls for NEET-PG:** * **Post-Influenza Pneumonia:** Think *S. aureus* if the patient deteriorates rapidly after initial improvement of flu symptoms [1]. * **Radiology:** *S. aureus* often shows bilateral patchy infiltrates, pneumatoceles (especially in children), and empyema. * **CA-MRSA:** Community-acquired MRSA strains often produce the **Panton-Valentine Leukocidin (PVL) toxin**, which causes tissue necrosis and severe hemorrhagic pneumonia.

Question 414: In an HIV-positive patient with Pneumocystis jiroveci infection, which of the following medications is used for its prevention?

A. Azithromycin
B. Acyclovir
C. Levofloxacin
D. Sulfamethoxazole + trimethoprim (Correct Answer)

Explanation: **Explanation:** **Pneumocystis jirovecii pneumonia (PCP)** is a major opportunistic infection in HIV-positive individuals, typically occurring when the **CD4 count falls below 200 cells/mm** [1]. **Why Option D is Correct:** **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, also known as Co-trimoxazole, is the **gold standard** for both the treatment and prophylaxis of PCP [1]. It works by inhibiting sequential steps in the folate synthesis pathway of the fungus. Prophylaxis is indicated in HIV patients with a CD4 count <200 cells/mm or a history of oropharyngeal candidiasis. **Why Other Options are Incorrect:** * **A. Azithromycin:** This is the drug of choice for the prophylaxis of *Mycobacterium avium complex* (MAC), usually initiated when the CD4 count drops below 50 cells/mm. * **B. Acyclovir:** This is an antiviral used for treating Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV) infections; it has no activity against fungal pathogens like *P. jirovecii*. * **C. Levofloxacin:** This is a fluoroquinolone antibiotic used for bacterial infections (like community-acquired pneumonia). While it has broad-spectrum antibacterial activity, it is ineffective against *P. jirovecii*. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** TMP-SMX is the DOC for both prophylaxis and treatment [1]. * **Alternative for Prophylaxis:** If a patient is allergic to sulfa drugs, **Dapsone** or **Atovaquone** can be used [1]. * **Alternative for Treatment:** For moderate-to-severe PCP, **Primaquine + Clindamycin** or **Pentamidine** are alternatives. * **Steroid Indication:** Adjuvant corticosteroids (Prednisone) are added to treatment if **PaO₂ < 70 mmHg** or **A-a gradient > 35 mmHg** to prevent inflammation-induced respiratory failure [1]. * **Chest X-ray Finding:** Classically shows bilateral perihilar "ground-glass" opacities or interstitial infiltrates [1].

Question 415: What is the most common opportunistic infection in AIDS?

A. Tuberculosis (Correct Answer)
B. Cryptococcosis
C. Pneumocystis jirovecii pneumonia
D. Histoplasmosis

Explanation: **Explanation:** The correct answer is **Tuberculosis (TB)**. In the context of the global HIV epidemic, particularly in developing countries like India, *Mycobacterium tuberculosis* is the most common opportunistic infection (OI) and the leading cause of mortality among AIDS patients [1]. Unlike many other OIs, TB can occur at any CD4 count, although its clinical presentation becomes more atypical (extrapulmonary or disseminated) as the CD4 count declines [1]. **Analysis of Options:** * **Tuberculosis (A):** Globally and in India, TB is the most prevalent OI. It is often the first sign of HIV infection and significantly accelerates the progression of HIV to AIDS. * **Pneumocystis jirovecii pneumonia (C):** Historically, PCP was the most common opportunistic infection in the Western world before the widespread use of prophylactic Co-trimoxazole and ART [1]. It typically occurs when CD4 counts drop below 200 cells/µL [1]. * **Cryptococcosis (B) & Histoplasmosis (D):** These are fungal OIs that generally occur in advanced stages of immunosuppression (CD4 <100 cells/µL). While significant, their prevalence is much lower than that of TB. **NEET-PG High-Yield Pearls:** * **Most common OI in India/Worldwide:** Tuberculosis. * **Most common opportunistic "Malignancy" in AIDS:** Kaposi Sarcoma (caused by HHV-8). * **Most common "Fungal" OI:** Candidiasis (Oral Thrush). * **Most common "Life-threatening" Fungal OI:** *Pneumocystis jirovecii*. * **CD4 Thresholds:** * <200: *Pneumocystis jirovecii* (Start Co-trimoxazole prophylaxis). * <100: Toxoplasmosis, Cryptococcosis. * <50: Mycobacterium avium complex (MAC), CMV Retinitis.

Question 416: A 60-year-old patient with a past history of treated pulmonary tuberculosis presents with massive hemoptysis. What is the most likely cause of hemoptysis?

A. Pulmonary amyloidosis
B. Aspergilloma (Correct Answer)
C. Bronchiolitis
D. Relapse of tuberculosis

Explanation: The most likely cause of massive hemoptysis in a patient with a history of treated pulmonary tuberculosis is an **Aspergilloma** (Fungal Ball) [1], [2]. **1. Why Aspergilloma is correct:** Tuberculosis often leaves behind residual **cavitary lesions** in the upper lobes. *Aspergillus fumigatus* can colonize these pre-existing cavities, forming a "fungal ball" composed of hyphae, mucus, and cellular debris [1]. Massive hemoptysis occurs because the fungus produces proteolytic enzymes and toxins (like gliotoxin) that erode the bronchial arteries or the highly vascularized granulation tissue lining the cavity wall [2]. **2. Why other options are incorrect:** * **Pulmonary Amyloidosis:** While chronic inflammation (like TB) can lead to secondary (AA) amyloidosis, it typically involves the kidneys or liver. Isolated pulmonary amyloidosis is rare and seldom presents with massive hemoptysis. * **Bronchiolitis:** This is an inflammatory condition of the small airways, usually viral or irritant-induced, presenting with wheezing and dyspnea rather than massive hemorrhage. * **Relapse of Tuberculosis:** While a relapse can cause hemoptysis, it is usually associated with constitutional symptoms (fever, night sweats, weight loss). In a stable patient with a history of "treated" TB presenting with sudden, massive bleeding, Aspergilloma is statistically more common [2]. **Clinical Pearls for NEET-PG:** * **Monod Sign:** A radiolucent crescent of air surrounding a solid mass within a cavity on Chest X-ray/CT, pathognomonic for Aspergilloma [1]. * **Treatment of Choice:** Surgical resection is the definitive treatment for symptomatic Aspergilloma. If the patient is unfit for surgery, **Bronchial Artery Embolization (BAE)** is the preferred emergency procedure to control massive hemoptysis. * **Definition:** Massive hemoptysis is generally defined as >200–600 mL of blood in 24 hours.

Question 417: Which morphological form of Leishmania donovani is seen in humans?

A. Promastigote
B. Trypomastigote
C. Amastigote (Correct Answer)
D. Epimastigote

Explanation: **Explanation:** *Leishmania donovani*, the causative agent of Visceral Leishmaniasis (Kala-azar), exists in two distinct morphological stages during its life cycle: the **Amastigote** and the **Promastigote**. [1] **1. Why Amastigote is correct:** The **Amastigote** (LD body) is the form found in **humans** and other mammalian hosts. [1] It is an intracellular, non-flagellated, oval or round structure (2–4 µm). After the sandfly injects the parasite, it is engulfed by macrophages of the Reticuloendothelial system (spleen, liver, bone marrow). Inside the phagolysosome, it transforms into the amastigote form to multiply by binary fission. **2. Why the other options are incorrect:** * **Promastigote:** This is the flagellated, motile form found in the **Sandfly** (vector) and in artificial culture media (e.g., NNN medium). [1] It is the infective stage for humans. [1] * **Trypomastigote:** This stage is characteristic of the genus *Trypanosoma* (e.g., *T. brucei* and *T. cruzi*). It is found in the blood of humans in African Trypanosomiasis. * **Epimastigote:** This is a developmental stage found in the insect vector for *Trypanosoma* species, not *Leishmania*. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Female Sandfly (*Phlebotomus argentipes*). * **Infective Form:** Promastigote; **Diagnostic Form:** Amastigote. [1] * **Gold Standard Diagnosis:** Splenic aspirate (highest yield) or Bone marrow biopsy to visualize LD bodies. [1] * **Culture:** NNN (Novy-MacNeal-Nicolle) medium shows Promastigotes. [1] * **Drug of Choice:** Liposomal Amphotericin B.

Question 418: Sterile pyuria is characteristically seen in which of the following conditions?

A. Renal Tuberculosis (Correct Answer)
B. Chronic Hydronephrosis
C. Wilm's Tumor
D. Neuroblastoma

Explanation: **Explanation:** **Sterile pyuria** is defined as the presence of white blood cells (pus cells) in the urine (>5 WBCs/hpf) in the absence of growth on standard aerobic culture media. **Renal Tuberculosis (Correct Answer):** Renal TB is the most common cause of sterile pyuria. *Mycobacterium tuberculosis* does not grow on standard culture media (like MacConkey or Blood Agar) used for routine UTIs. The infection causes chronic granulomatous inflammation and ulceration of the urothelium, leading to the constant shedding of WBCs into the urine [1]. Diagnosis requires specialized media (Lowenstein-Jensen) or liquid cultures (MGIT). **Incorrect Options:** * **Chronic Hydronephrosis:** This is a structural dilatation of the renal pelvis and calyces [2]. While it predisposes to infection, it does not characteristically cause pyuria unless a secondary bacterial infection (which would grow on standard culture) is present. * **Wilm’s Tumor & Neuroblastoma:** These are pediatric malignancies. While they may present with hematuria (blood in urine) or an abdominal mass, they do not typically present with pyuria. **High-Yield Clinical Pearls for NEET-PG:** * **Other causes of Sterile Pyuria:** Partially treated bacterial UTI (most common overall), Chlamydia/Ureaplasma, Renal stones, Kawasaki disease, and Analgesic nephropathy. * **Early sign of Renal TB:** Microscopic hematuria and sterile pyuria [1]. * **Late sign of Renal TB:** "Putty kidney" (autonephrectomy) due to caseous necrosis and calcification. * **Gold Standard Diagnosis:** Urine culture for Acid-Fast Bacilli (AFB) – requires 3 to 5 consecutive early morning midstream urine samples.

Question 419: All are true regarding typhoid fever, except?

A. Peak incidence in 30-50 years (Correct Answer)
B. No non-human reservoir
C. Carriers can exist for years
D. Lifelong immunity cannot be acquired

Explanation: **Explanation:** Typhoid fever, caused by *Salmonella Typhi*, is a systemic infection primarily transmitted via the feco-oral route. **1. Why Option A is the Correct Answer (The False Statement):** The peak incidence of typhoid fever is **not** in the 30–50 age group. It is primarily a disease of **children and young adults**, with the highest incidence typically seen in the **5–19 years** age group. In endemic areas, children under 5 also carry a significant burden. By age 30, many individuals have developed partial immunity due to repeated subclinical exposures. **2. Analysis of Other Options:** * **Option B (No non-human reservoir):** This is **true**. *Salmonella Typhi* and *Paratyphi* are strictly human pathogens. There are no animal or environmental reservoirs; transmission occurs only from human cases or carriers. * **Option C (Carriers can exist for years):** This is **true**. Approximately 1–5% of patients become chronic carriers (defined as excreting bacilli in stools for >1 year). The **gallbladder** is the most common site of colonization, often associated with gallstones. * **Option D (Lifelong immunity cannot be acquired):** This is **true**. Natural infection does not confer permanent immunity. Re-infection can occur if the inoculum size is large, which is why vaccination and sanitation remain critical even in previously infected individuals. **NEET-PG High-Yield Pearls:** * **Investigation of Choice:** Blood culture is the gold standard in the 1st week; Stool culture in the 3rd week. * **Pathognomonic sign:** Rose spots (seen in the 2nd week). * **Drug of Choice:** Ceftriaxone (due to widespread multidrug resistance to Ciprofloxacin). * **Carrier State:** More common in females and those with biliary tract abnormalities. Treatment of choice for carriers is Ciprofloxacin for 6 weeks or Cholecystectomy.

Question 420: A 27-year-old man with HIV presents with odynophagia. He is not on antiretroviral therapy and is otherwise asymptomatic. Examination of the mouth and pharynx is normal. What is the most likely diagnosis?

A. Midesophageal cancer
B. Distal esophageal cancer
C. Peptic stricture
D. Candida infection (Correct Answer)

Explanation: **Explanation:** **Why Candida infection is correct:** In a patient with HIV presenting with **odynophagia** (painful swallowing), the most common cause is **Esophageal Candidiasis**. It is an AIDS-defining illness and typically occurs when the CD4 count falls below 200 cells/mm3. A crucial clinical point for NEET-PG is that while oral thrush often coexists, its absence (as seen in this patient's normal mouth exam) does **not** rule out esophageal involvement [1]. In HIV patients with odynophagia, the standard of care is an empirical trial of **Fluconazole**. If symptoms persist, endoscopy is performed to look for other causes like CMV (large solitary ulcers) or HSV (multiple small "punched-out" ulcers). **Why incorrect options are wrong:** * **Options A & B (Esophageal Cancer):** While HIV patients have a higher risk of various malignancies, esophageal cancer typically presents with progressive **dysphagia** (difficulty swallowing) and weight loss in older patients, rather than acute odynophagia in a 27-year-old. * **Option C (Peptic Stricture):** This is a complication of chronic GERD. It presents with gradual dysphagia to solids and would be unlikely to present as isolated odynophagia in a young HIV-positive patient without a long history of reflux. **Clinical Pearls for NEET-PG:** 1. **Most common cause of esophagitis in HIV:** *Candida albicans* [1]. 2. **Diagnostic triad:** HIV + Odynophagia + Oral Thrush (though thrush is absent in ~20% of cases). 3. **Endoscopy findings:** White, adherent plaques (pseudomembranes) on an erythematous base. 4. **Management:** Oral Fluconazole (14–21 days). If no response in 3–5 days, perform endoscopy with biopsy/cytology.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Antimicrobial Resistance

Practice Questions

Vaccination Principles

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free