Infectious Diseases Practice Questions

Q: A previously healthy 43-year-old man presents with symptoms of cough, fever, weight loss, and lymphadenopathy for the past 2 months. His physical examination reveals multiple axillary and cervical lymph nodes and oropharyngeal ulcerations. His CXR reveals fibronodular pulmonary infiltrates in the apex, his sputum is negative for TB, and the HIV test is negative. A bronchoalveolar lavage (BAL) confirms the diagnosis. For the above patient, select the most likely diagnosis?

histoplasmosis. **Explanation:** The clinical presentation of chronic cough, fever, weight loss, and apical fibronodular infiltrates closely mimics pulmonary tuberculosis [1]. However, the presence of **oropharyngeal ulcerations** and generalized **lymphadenopathy** in a TB-negative patient is a classic hallmark of **Histoplasmosis** (*Histoplasma capsulatum*). 1. **Why Histoplasmosis is correct:** While often associated with immunocompromised states (HIV), Histoplasmosis can occur in immunocompetent individuals. It is a dimorphic fungus that primarily affects the lungs but can disseminate to the reticuloendothelial system (lymph nodes, liver, spleen) and mucous membranes. Oropharyngeal ulcers are a high-yield diagnostic clue for disseminated or chronic histoplasmosis. 2. **Why other options are incorrect:** * **Brucellosis:** Typically presents with undulant fever, arthralgia, and hepatosplenomegaly, but does not usually cause apical pulmonary infiltrates or oropharyngeal ulcers. * **Coccidioidomycosis:** Known as "Valley Fever," it causes pulmonary symptoms and erythema nodosum, but oropharyngeal ulceration is not a characteristic feature. * **Leprosy:** While it involves skin and nerves, it does not present with apical pulmonary fibronodular infiltrates or acute systemic symptoms like weight loss and fever mimicking TB [2]. **NEET-PG High-Yield Pearls:** * **The "Great Mimicker":** Histoplasmosis is the fungal equivalent of Tuberculosis. * **Morphology:** On biopsy/BAL, look for **small intracellular yeast cells** within macrophages (Gomori Methenamine Silver stain). * **Habitat:** Associated with **bird or bat droppings** (caving, cleaning chicken coops). * **Treatment:** Mild cases may resolve spontaneously; moderate-to-severe cases require **Itraconazole**, while disseminated disease requires **Amphotericin B**.

Q: A 30-year-old patient has persistent antibodies to HCV for 6 months with normal AST/ALT levels and no symptoms or stigmata of liver disease. What is the most appropriate next step in management?

Determine HCV RNA levels. ### Explanation The presence of **HCV antibodies (Anti-HCV)** indicates that the patient has been exposed to the Hepatitis C virus at some point. However, it does not distinguish between an active (chronic) infection and a resolved past infection [1]. **1. Why Option D is Correct:** In Hepatitis C, approximately 15–25% of patients clear the virus spontaneously but remain antibody-positive for life [1]. Furthermore, chronic HCV infection is often "clinically silent," where patients may have **persistently normal ALT/AST levels** despite ongoing viral replication and progressive liver fibrosis [1]. Therefore, the presence of antibodies must always be followed by a **qualitative or quantitative HCV RNA test (PCR)** to confirm active viremia [1]. If HCV RNA is detected, the patient has chronic hepatitis C and requires treatment, regardless of enzyme levels. **2. Why Other Options are Incorrect:** * **Option A & B:** Reassurance or simply repeating antibody titers is inappropriate because the patient may have active, transmissible chronic infection that can lead to cirrhosis or HCC if left untreated. Antibody titers do not correlate with disease activity. * **Option C:** Normal liver enzymes are not a reliable indicator of viral clearance. Up to 30% of patients with chronic HCV have normal ALT levels. Relying on enzymes alone would miss a significant number of chronic cases. **Clinical Pearls for NEET-PG:** * **Screening Test:** Anti-HCV (ELISA). * **Confirmatory/Gold Standard for Active Infection:** HCV RNA by PCR [1]. * **Treatment Goal:** Sustained Virologic Response (SVR), defined as undetectable HCV RNA 12–24 weeks after completing antiviral therapy. * **High-Yield Fact:** Unlike Hepatitis B, Hepatitis C does not integrate into the host genome; therefore, it is potentially curable with Direct-Acting Antivirals (DAAs).

Q: Primary tuberculosis most commonly involves which organ?

Lung. **Explanation:** **Primary Tuberculosis (TB)** occurs in a person who has not been previously exposed to *Mycobacterium tuberculosis*. The most common route of transmission is the inhalation of infectious airborne droplets (droplet nuclei) [1]. 1. **Why Lung is Correct:** Since the primary mode of infection is inhalation, the **Lung** is the most common site of primary tuberculosis [1]. When the bacilli reach the subpleural area of the mid or lower lung zones, they form a **Ghon focus** [1]. When this is associated with involved hilar lymph nodes, it is termed the **Ghon complex** (or Primary Complex) [1]. In most cases, this lesion heals, leaving a calcified nodule known as a **Ranke complex** [1]. 2. **Why Other Options are Incorrect:** * **Brain:** CNS involvement (like TB meningitis) is a severe form of disseminated or miliary TB [2], but it is never the primary site of entry [4]. * **Lymph node:** While lymphadenopathy (especially hilar) is a component of the primary complex [1], the lung parenchyma is the initial site of deposition. Extrapulmonary lymph node TB (Scrofula) is common in secondary TB or reactivation [3]. * **Intestine:** This was historically common due to the ingestion of *M. bovis* via unpasteurized milk (Primary Intestinal TB), but with modern pasteurization, it is now rare compared to the pulmonary route. **High-Yield Clinical Pearls for NEET-PG:** * **Ghon Focus:** Subpleural lesion, usually in the lower part of the upper lobe or upper part of the lower lobe [1]. * **Ranke Complex:** Ghon complex + Calcification [1]. * **Simon’s Focus:** Secondary TB focus at the lung apex (due to high oxygen tension). * **Most common site of Extrapulmonary TB:** Lymph nodes (Tuberculous lymphadenitis) [3]. * **Most common site of Hematogenous spread:** Bone marrow.

Q: Basal exudates, infarcts, and hydrocephalus are findings observed in brain imaging studies. The most likely diagnosis is:

Tubercular Meningitis. ### Explanation The correct answer is **Tubercular Meningitis (TBM)**. This diagnosis is characterized by a classic triad of neuroimaging findings: 1. **Basal Exudates:** *Mycobacterium tuberculosis* has a predilection for the base of the brain. The inflammatory response leads to thick, gelatinous exudates in the basal cisterns, which can entrap cranial nerves [1]. 2. **Infarcts:** The intense inflammation causes **Vasculitis** (specifically affecting the Circle of Willis), leading to ischemic strokes, most commonly in the basal ganglia and internal capsule (Medial Striate artery territory). 3. **Hydrocephalus:** Exudates obstruct the flow of CSF at the level of the aqueduct or the basal cisterns, leading to **communicating or non-communicating hydrocephalus**. #### Why the other options are incorrect: * **Viral Meningitis:** Typically presents with normal imaging or mild meningeal enhancement. It does not cause thick exudates or infarcts. * **Herpes Encephalitis (HSV-1):** Characteristically involves the **temporal lobes** and limbic system. Imaging shows edema and hemorrhage in the temporal/frontal lobes, not basal exudates. * **Cerebral Malaria:** Imaging is often normal or shows diffuse cerebral edema. While micro-hemorrhages (Durck’s granulomas) can occur, the classic triad of TBM is absent. #### NEET-PG High-Yield Pearls: * **Gold Standard Diagnosis:** CSF Culture (MGIT) or GeneXpert (NAAT). * **CSF Findings in TBM:** High protein, low sugar, and **lymphocytic pleocytosis** [1]. * **Hydrocephalus Management:** Often requires a VP shunt; steroids (Dexamethasone) are added to ATT to reduce mortality and complications from exudates. * **Stage of TBM:** The presence of infarcts or altered sensorium usually indicates Stage II or III disease.

Q: Apex of the lung is commonly involved by which pathogen?

Klebsiella. **Explanation:** **Why Klebsiella is Correct:** *Klebsiella pneumoniae* is a Gram-negative encapsulated bacillus that typically causes severe, necrotizing lobar pneumonia. It has a strong predilection for the **upper lobes**, particularly the **apex of the lung**. This is attributed to the organism's tendency to cause infection in patients with impaired host defenses (e.g., chronic alcoholics, diabetics), where aspiration of oropharyngeal flora occurs [1]. The resulting inflammatory response is so intense that it leads to "bulging fissures" on X-ray due to heavy alveolar exudate. **Analysis of Incorrect Options:** * **Chlamydia:** *Chlamydia pneumoniae* typically causes "atypical pneumonia" characterized by diffuse, patchy interstitial infiltrates rather than localized apical consolidation [1]. * **Coxiella burnetii:** The causative agent of Q fever usually presents with non-specific radiological findings, most commonly multiple rounded opacities or segmental consolidation in the **lower lobes**. * **Actinomyces israelii:** While *Actinomyces* can cross anatomical boundaries and involve the pleura or chest wall, it most commonly involves the **lower lobes** via aspiration [1]. It is known for causing "sulfur granules" in abscesses rather than isolated apical pneumonia. **High-Yield Clinical Pearls for NEET-PG:** * **"Currant Jelly" Sputum:** A classic board-style descriptor for *Klebsiella* pneumonia due to blood and mucus. * **Friedländer’s Pneumonia:** An older eponym for *Klebsiella* pneumonia. * **Differential Diagnosis for Apical Lesions:** Remember the mnemonic **"SET"** for upper lobe involvement: **S**ilicosis, **E**xtrinsic allergic alveolitis, and **T**uberculosis (the most common cause of apical cavitary lesions). *Klebsiella* is the classic bacterial (non-TB) cause. * **Alcoholism Link:** Always suspect *Klebsiella* in an alcoholic patient presenting with sudden onset of productive cough and upper lobe consolidation [1].

Q: Regarding Hepatitis E, which of the following statements is true?

Mortality is increased in pregnancy.. **Explanation:** **Hepatitis E Virus (HEV)** is a non-enveloped, **single-stranded RNA virus** primarily transmitted via the fecal-oral route. It is a major cause of acute viral hepatitis worldwide, particularly in developing countries with poor sanitation. **Why Option D is correct:** The most characteristic clinical feature of HEV is its high virulence in pregnant women, especially during the **third trimester**. While the overall mortality rate for HEV is low (0.5–4%), it escalates dramatically to **15–25% in pregnancy**. This is attributed to a combination of altered immune responses (Th2 shift), high viral loads, and a predisposition to **Fulminant Hepatic Failure (FHF)** and Disseminated Intravascular Coagulation (DIC). **Why other options are incorrect:** * **Option A:** Hepatitis **D** (Delta virus) is the one that requires Hepatitis B (HBsAg) for its replication and infection. HEV is independent. * **Option B:** HEV is an **RNA virus** (Hepeviridae family). Hepatitis B is the only major hepatitis virus that is a DNA virus. * **Option C:** While HEV can occur in HIV patients (potentially leading to chronic hepatitis in immunocompromised states), there is no specific mandatory co-infection or epidemiological link like that seen between HBV/HCV and HIV. **High-Yield Pearls for NEET-PG:** * **Transmission:** Fecal-oral (similar to Hep A). * **Genotypes:** Genotypes 1 and 2 are human-restricted (epidemic); Genotypes 3 and 4 are zoonotic (pigs/boars) and can cause **chronic hepatitis** in transplant recipients. * **Diagnosis:** IgM anti-HEV is the gold standard for acute infection. * **Extra-hepatic manifestations:** Guillain-Barré syndrome and Neuralgic amyotrophy.

Question 1

A previously healthy 43-year-old man presents with symptoms of cough, fever, weight loss, and lymphadenopathy for the past 2 months. His physical examination reveals multiple axillary and cervical lymph nodes and oropharyngeal ulcerations. His CXR reveals fibronodular pulmonary infiltrates in the apex, his sputum is negative for TB, and the HIV test is negative. A bronchoalveolar lavage (BAL) confirms the diagnosis. For the above patient, select the most likely diagnosis?

Accepted Answer

histoplasmosis

Answer

brucellosis

Answer

coccidioidomycosis

Answer

leprosy

Question 2

A 30-year-old patient has persistent antibodies to HCV for 6 months with normal AST/ALT levels and no symptoms or stigmata of liver disease. What is the most appropriate next step in management?

Accepted Answer

Determine HCV RNA levels

Answer

Reassure the patient

Answer

Repeat antibody titre every three years

Answer

Repeat liver enzymes every year

Question 3

Primary tuberculosis most commonly involves which organ?

Accepted Answer

Lung

Answer

Brain

Answer

Lymph node

Answer

Intestine

Question 4

A patient on a urinary catheter has a catheter tip culture that shows extended-spectrum beta-lactamase (ESBL)-positive Klebsiella. Which of the following drugs can be given?

Accepted Answer

A beta-lactamase inhibitor

Answer

Ceftriaxone

Answer

Aminoglycoside

Answer

Tetracycline

Question 5

Which of the following is NOT true about Pneumocystis jirovecii pneumonia?

Accepted Answer

Associated with an increased alveolar-arterial oxygen gradient (PAO2 - PaO2)

Answer

Characterized by respiratory alkalosis

Answer

Associated with decreased diffusion capacity

Answer

Leads to cyanosis

Question 6

Basal exudates, infarcts, and hydrocephalus are findings observed in brain imaging studies. The most likely diagnosis is:

Accepted Answer

Tubercular Meningitis

Answer

Viral Meningitis

Answer

Herpes encephalitis

Answer

Cerebral Malaria

Question 7

Which of the following is the best method to evaluate alpha interferon therapy for Hepatitis C Virus (HCV) infection?

Accepted Answer

Quantification of HCV RNA

Answer

ALT and AST levels

Answer

Serum bilirubin level

Answer

Serum IgM and IgG levels

Question 8

Apex of the lung is commonly involved by which pathogen?

Accepted Answer

Klebsiella

Answer

Chlamydia

Answer

Coxiella burnetti

Answer

Actinomyces israelii

Question 9

Regarding Hepatitis E, which of the following statements is true?

Accepted Answer

Mortality is increased in pregnancy.

Answer

It occurs with Hepatitis B.

Answer

It is a single-stranded DNA virus.

Answer

It occurs along with HIV.

Question 10

Which of the following statements regarding HIV-associated TB is FALSE?

Accepted Answer

Patients with both HIV infection and TB are more infectious than persons without HIV co-infection.

Answer

Extrapulmonary TB is common among HIV-infected patients.

Answer

The diagnosis of TB in HIV-infected patients may be difficult.

Answer

Immune reconstitution inflammatory syndrome (IRIS) is more common among patients with advanced immunosuppression and extrapulmonary TB.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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