Infectious Diseases Practice Questions

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

Sulfamethoxazole + trimethoprim. **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 35 mmHg** to prevent inflammation-induced respiratory failure [1]. * **Chest X-ray Finding:** Classically shows bilateral perihilar "ground-glass" opacities or interstitial infiltrates [1].

Q: 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?

Aspergilloma. 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.

Q: Pleural effusion without evident lung infiltration is most often due to which of the following conditions?

Tuberculosis. ### Explanation **Correct Answer: D. Tuberculosis** **Medical Concept:** In the context of a pleural effusion occurring without visible lung parenchymal infiltration (a "clear" lung field on X-ray), **Tuberculous Pleurisy** is the most common cause, especially in endemic regions like India. This typically occurs as a primary manifestation of TB due to the rupture of a subpleural caseous focus into the pleural space [1]. This triggers a **delayed-type hypersensitivity reaction** rather than a widespread pulmonary infection, which explains why the underlying lung often appears normal on imaging. **Analysis of Incorrect Options:** * **A. Viral Pleurisy:** While it can cause pleuritic chest pain and small effusions, it is rarely the "most common" cause of a significant isolated effusion compared to TB in the NEET-PG context. * **B. Lymphoma:** This can cause isolated effusions (often chylous or due to lymphatic obstruction), but it is statistically less common than TB or metastatic carcinoma. * **C. Carcinoma:** While malignancy is a leading cause of exudative effusion, it is frequently associated with a visible primary lung mass, hilar lymphadenopathy, or multiple nodules [1]. TB remains the classic answer for "isolated" effusion in young to middle-aged patients. **High-Yield Clinical Pearls for NEET-PG:** * **Biochemical Profile:** TB effusion is typically an **exudate** with high protein (>3g/dL) and **lymphocytic predominance** [1]. * **ADA Levels:** Adenosine Deaminase (ADA) > 40 U/L is highly suggestive of TB. * **Gold Standard Diagnosis:** Pleural biopsy (showing granulomas) has a higher yield than pleural fluid culture or cytology, as the fluid is often paucibacillary [1]. * **Light’s Criteria:** Always remember these to differentiate exudate from transudate (Fluid/Serum Protein >0.5, Fluid/Serum LDH >0.6) [1].

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

Amastigote. **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.

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

Renal Tuberculosis. **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.

Q: 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?

Candida infection. **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.

Q: What is the highest relative risk of developing active tuberculosis in patients already infected with Mycobacterium tuberculosis?

Post organ transplantation. **Explanation:** The risk of progression from latent tuberculosis infection (LTBI) to active disease depends on the degree of host immune suppression. **1. Why Post-Organ Transplantation is Correct:** Patients undergoing solid organ transplantation (SOT) represent the highest risk group [2]. This is due to the use of potent **T-cell suppressive induction and maintenance therapy** (e.g., calcineurin inhibitors, corticosteroids, and anti-thymocyte globulin). Since the control of *M. tuberculosis* is primarily mediated by **Th1-cell-mediated immunity**, profound iatrogenic suppression increases the relative risk (RR) of reactivation to approximately **20–74 times** that of the general population. **2. Analysis of Incorrect Options:** * **Diabetes Mellitus (A):** While DM impairs neutrophil function and cytokine production, the RR is relatively low (approx. **2–4**) [2]. * **Recent Infection (B):** The risk is highest in the first 2 years after primary infection (approx. 5% risk in the first 2 years) [2], but this does not exceed the risk posed by severe pharmacological immunosuppression. * **Malnutrition (D):** Protein-energy malnutrition impairs cell-mediated immunity, but the RR (approx. **2–3**) is significantly lower than that of transplant recipients [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Highest Overall Risk:** HIV infection (especially with low CD4 counts) and Organ Transplantation are the top two risk factors for progression [1]. * **TNF-α Inhibitors:** Patients on Infliximab or Etanercept also have a very high RR (approx. 1.8–12) and must be screened for LTBI before starting therapy. * **Silicosis:** This is a classic occupational risk factor with a high RR (approx. 30) due to impaired macrophage function [2]. * **The "Rule of 10":** In an immunocompetent individual, the lifetime risk of reactivation is 10%; in an HIV-positive individual, the risk is 10% **per year** [1].

Question 1

Which of the following statements regarding amebic dysentery is true?

Accepted Answer

Diagnostic mucosal findings are typically observed on sigmoidoscopy.

Answer

The incubation period is typically 7-10 days.

Answer

It is characterized by profuse, watery diarrhea.

Answer

The diagnostic mucosal lesion is most commonly found in the rectum.

Question 2

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

Accepted Answer

Sulfamethoxazole + trimethoprim

Answer

Azithromycin

Answer

Acyclovir

Answer

Levofloxacin

Question 3

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?

Accepted Answer

Aspergilloma

Answer

Pulmonary amyloidosis

Answer

Bronchiolitis

Answer

Relapse of tuberculosis

Question 4

Pleural effusion without evident lung infiltration is most often due to which of the following conditions?

Accepted Answer

Tuberculosis

Answer

Viral pleurisy

Answer

Lymphoma

Answer

Carcinoma

Question 5

Which morphological form of Leishmania donovani is seen in humans?

Accepted Answer

Amastigote

Answer

Promastigote

Answer

Trypomastigote

Answer

Epimastigote

Question 6

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

Accepted Answer

Renal Tuberculosis

Answer

Chronic Hydronephrosis

Answer

Wilm's Tumor

Answer

Neuroblastoma

Question 7

A resident doctor, not immunized against Hepatitis B, sustains an accidental needle-stick injury from a patient positive for HBsAg. What is the recommended next step?

Accepted Answer

Administer hepatitis B immunoglobulin and complete the course of hepatitis B vaccine

Answer

Administer hepatitis B immunoglobulin

Answer

Complete the course of hepatitis B vaccine

Answer

Observation

Question 8

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?

Accepted Answer

Candida infection

Answer

Midesophageal cancer

Answer

Distal esophageal cancer

Answer

Peptic stricture

Question 9

What is the highest relative risk of developing active tuberculosis in patients already infected with Mycobacterium tuberculosis?

Accepted Answer

Post organ transplantation

Answer

Diabetes mellitus

Answer

Recent infection

Answer

Malnutrition

Question 10

A 30-year-old male presents with a cough and fever of six weeks' duration. Sputum smears are negative, and chest X-ray shows no significant findings. Given a high clinical suspicion for tuberculosis, what is the next appropriate management step?

Accepted Answer

Perform CBNAAT

Answer

Repeat chest X-ray

Answer

Start anti-tuberculosis treatment (ATT)

Answer

Repeat sputum examination

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?