Infectious Diseases Practice Questions

Q: Skin testing with tuberculin-PPD is most widely used in screening for:

Latent M. tuberculosis infection. ### Explanation **1. Why the Correct Answer is Right:** The Tuberculin Skin Test (TST) or Mantoux test is based on a **Type IV (Delayed-type) Hypersensitivity reaction**. When PPD (Purified Protein Derivative) is injected intradermally, it triggers sensitized T-cells in individuals previously exposed to *M. tuberculosis*. The primary clinical utility of the TST is to identify individuals with **Latent Tuberculosis Infection (LTBI)**—those who are infected but do not have active disease. In these patients, the immune system has successfully "contained" the bacilli, but memory T-cells remain, leading to a positive skin reaction. **2. Why the Incorrect Options are Wrong:** * **Active TB (Option A):** While a TST can be positive in active TB, it is **not** a diagnostic tool for it. Diagnosis of active TB requires clinical, radiological, and microbiological (Sputum AFB/CBNAAT) evidence. Furthermore, up to 25% of patients with active TB may show a false-negative TST due to "anergy." * **Miliary and Overwhelming TB (Options C & D):** In severe, disseminated forms of tuberculosis, the body’s cell-mediated immunity is often profoundly suppressed or overwhelmed. This leads to a state of **anergy**, where the TST frequently yields a **false-negative** result despite a high bacterial load. **3. High-Yield Clinical Pearls for NEET-PG:** * **Reading the test:** Results are read after **48–72 hours**. Only the **induration** (palpable hardness) is measured, not the erythema. * **False Positive:** Most commonly caused by prior **BCG vaccination** or infection with Nontuberculous Mycobacteria (NTM). * **False Negative (Anergy):** Seen in malnutrition, HIV/AIDS, sarcoidosis, miliary TB, and recent viral infections (e.g., Measles). * **Alternative:** The **IGRA (Interferon-Gamma Release Assay)** is more specific than TST as it does not cross-react with the BCG vaccine.

Q: Tuberculosis in HIV infection causes pulmonary disease resembling post-primary disease in normal individuals when it occurs during which stage of HIV infection?

Stage of viraemia. The clinical presentation of Tuberculosis (TB) in HIV-infected patients is directly dependent on the patient's degree of immunosuppression (CD4 count). [1] **1. Why "Stage of Viraemia" is correct:** The "Stage of Viraemia" refers to the early phase of HIV infection (Acute HIV Syndrome) where the CD4 count is still relatively high (usually >500 cells/mm³). At this stage, the body’s cell-mediated immunity is sufficiently intact to mount a typical granulomatous response. Consequently, TB presents as **Post-Primary (Reactivation) disease**, characterized by: * Upper lobe infiltrates. [1] * Cavitary lesions. [1] * Positive sputum smears (high bacterial load). **2. Why the incorrect options are wrong:** * **Full-blown AIDS:** In late-stage HIV (CD4 <200 cells/mm³), the immune system cannot form organized granulomas or cavities. TB here resembles **Primary Disease**, presenting with lower lobe infiltrates, mediastinal lymphadenopathy, miliary spread, and frequent extrapulmonary involvement. [1] Sputum smears are often negative despite high severity. * **Window Period (Middle/Last Third):** The window period refers to the time between infection and the appearance of detectable antibodies. While viraemia occurs here, the term "Stage of Viraemia" specifically denotes the clinical phase where the immune system is still robust enough to mimic immunocompetent TB patterns. **Clinical Pearls for NEET-PG:** * **CD4 >500:** Post-primary pattern (Cavitation, Upper lobe). [1] * **CD4 <200:** Primary pattern (Lymphadenopathy, Miliary, Extrapulmonary). [1] * **Most common extrapulmonary site in HIV:** Lymph nodes (Scrofula). [2] * **IRIS (Immune Reconstitution Inflammatory Syndrome):** Paradoxical worsening of TB symptoms after starting ART due to a recovering immune system. Always start TB treatment *before* ART to reduce this risk.

Q: All of the following are known complications of tuberculous meningitis except?

Parkinsonism. **Explanation:** Tuberculous Meningitis (TBM) is characterized by a thick, gelatinous **exudate** that accumulates primarily at the **base of the brain** (basal cisterns). This unique pathology explains most of its clinical complications. **Why Parkinsonism is the correct answer:** While TBM can affect the basal ganglia via infarcts, **Parkinsonism** is not a recognized or classic complication of the disease. Movement disorders in TBM are rare; when they occur, they more commonly manifest as chorea or tremors in pediatric populations rather than true Parkinsonism. **Analysis of other options:** * **Cranial Nerve Palsy:** The dense basal exudates entrap and compress cranial nerves as they exit the brainstem. The **6th cranial nerve** (Abducens) is most commonly affected due to its long intracranial course, followed by the 3rd and 4th nerves. * **Ptosis:** This is a direct clinical manifestation of **3rd cranial nerve (Oculomotor) palsy**, which is a frequent result of the basal inflammatory process. * **Cerebral Infarction:** TBM causes **vasculitis** of the small and medium-sized arteries (especially the Circle of Willis and Middle Cerebral Artery). This leads to luminal narrowing and thrombosis, resulting in "tubercular zone" infarcts, typically in the basal ganglia and internal capsule. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hydrocephalus** is the most common complication of TBM (usually communicating type) [1]. 2. **Hyponatremia** in TBM is frequently caused by SIADH or Cerebral Salt Wasting Syndrome. 3. **Stage of TBM:** Medical management is most effective in Stage I (conscious, no focal deficits); prognosis worsens significantly by Stage III (coma/dense paraplegia). 4. **Diagnosis:** CSF typically shows high protein, low glucose, and **lymphocytic pleocytosis**.

Q: A 35-year-old pet shop worker developed progressively spreading nodular lesions. He was afebrile. What is the most likely causative organism?

Mycobacterium marinum. The clinical presentation of **progressively spreading nodular lesions** in a patient with occupational exposure to aquatic environments (pet shop worker/aquarium handler) is classic for **"Fish Tank Granuloma,"** caused by **Mycobacterium marinum**. **Why Mycobacterium marinum is correct:** * **Pathogenesis:** It is a non-tuberculous mycobacterium (NTM) found in fresh and salt water. It enters through minor skin abrasions. * **Clinical Presentation:** It typically presents as a localized granuloma or a series of nodules that follow a **sporotrichoid distribution** (spreading proximally along lymphatic drainage). * **Key Feature:** Patients are usually **afebrile**, and the lesions are chronic and slow-growing, matching the "progressive" nature described. **Why other options are incorrect:** * **Acinetobacter baumannii:** Typically causes opportunistic nosocomial infections (ventilator-associated pneumonia or UTIs), not chronic nodular skin lesions. * **Erysipelothrix rhusiopathiae:** Causes **Erysipeloid**, usually seen in fishermen or butchers. However, it presents as a well-demarcated, painful, purplish-red **erythematous plaque** (not nodules) and is often more acute. * **Pasteurella multocida:** Associated with **cat or dog bites**. It causes rapid-onset cellulitis (within 24 hours) with intense pain and swelling, rather than slow-spreading nodules. **NEET-PG High-Yield Pearls:** * **Sporotrichoid Spread:** Differential diagnosis includes *Sporothrix schenckii* (Rose gardener’s disease), *Mycobacterium marinum*, *Nocardia*, and *Leishmania*. * **Culture:** *M. marinum* grows best at a cooler temperature (**30-32°C**), explaining its predilection for the skin (extremities) rather than internal organs. * **Treatment:** Clarithromycin, ethambutol, or rifampin for several months.

Q: A patient presents with fever. Lumbar puncture is performed as part of the workup. Cerebrospinal fluid (CSF) analysis reveals high protein levels, normal glucose, and a marked increase in lymphocytes. What is the most likely diagnosis?

Tubercular meningitis. **Explanation:** The CSF profile described—**high protein, normal glucose, and lymphocytic pleocytosis**—is characteristic of a subacute or chronic inflammatory process, most classically **Tubercular Meningitis (TBM)** or Viral Meningitis. In TBM, the protein is typically very high (often >100 mg/dL) due to the exudative nature of the infection at the base of the brain [2], and while glucose *can* be low, it may remain within the normal range in early stages or less severe presentations [3]. **Analysis of Options:** * **A. Tubercular Meningitis (Correct):** Characterized by a lymphocytic predominant pleocytosis and significantly elevated protein. It is the most common cause of chronic meningitis in India [1]. * **B. Bacterial Meningitis:** Typically shows a **neutrophilic** (polymorphonuclear) leukocytosis, markedly **low glucose** (hypoglycorrhachia), and very high protein [3]. * **C. Partially Treated Pyogenic Infection:** This can mimic TBM as the cell type may shift from neutrophils to lymphocytes, but the glucose is usually low, and the clinical history would involve prior antibiotic use. * **D. Neurocysticercosis:** Usually presents with seizures rather than a febrile meningitic syndrome. CSF may show mild eosinophilia or be entirely normal unless there is an active racemose subarachnoid involvement. **NEET-PG High-Yield Pearls:** * **Cobweb Coagulum:** Formation in CSF on standing is highly suggestive of TBM (due to high fibrinogen). * **ADA (Adenosine Deaminase):** Levels >10 U/L in CSF are highly suggestive of TBM. * **Target Area:** TBM primarily affects the **basal cisterns**, leading to cranial nerve palsies (CN VI is most common) [2]. * **Gold Standard:** CSF Culture (MGIT) is the gold standard, though GeneXpert (CBNAAT) is the preferred initial rapid test.

Question 1

Skin testing with tuberculin-PPD is most widely used in screening for:

Accepted Answer

Latent M. tuberculosis infection

Answer

Active TB

Answer

Miliary TB

Answer

Overwhelming TB

Question 2

Resistant kala-azar is defined by the persistence of which of the following features despite adequate therapy?

Accepted Answer

L.D. bodies in more than 5% of cells in bone marrow

Answer

Fever

Answer

Non-regression of splenomegaly

Answer

Hyperglobulinaemia

Question 3

Tuberculosis in HIV infection causes pulmonary disease resembling post-primary disease in normal individuals when it occurs during which stage of HIV infection?

Accepted Answer

Stage of viraemia

Answer

Middle third of window period

Answer

Last third of window period

Answer

Full blown AIDS

Question 4

A 50-year-old diabetic and hypertensive male presented with diplopia for 1 day, along with facial swelling and difficulty in speaking. The patient was in distress. On examination, he was febrile, hypertensive, and tachycardic, with right-sided proptosis, facial edema, and facial palsy. Laboratory findings revealed leukocytosis, increased serum glucose, and deranged RFTs. Cytopathology was taken on site. All of the following can be used in the management of the above condition except?

Accepted Answer

Voriconazole

Answer

Insulin

Answer

Hemodialysis

Answer

Amphotericin B

Question 5

All of the following are known complications of tuberculous meningitis except?

Accepted Answer

Parkinsonism

Answer

Cranial nerve palsy

Answer

Cerebral infarction

Answer

Ptosis

Question 6

A 35-year-old pet shop worker developed progressively spreading nodular lesions. He was afebrile. What is the most likely causative organism?

Accepted Answer

Mycobacterium marinum

Answer

Acinetobacter baumannii

Answer

Erysipelothrix rhusiopathiae

Answer

Pasteurella multocida

Question 7

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 8

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 9

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 10

A patient presents with fever. Lumbar puncture is performed as part of the workup. Cerebrospinal fluid (CSF) analysis reveals high protein levels, normal glucose, and a marked increase in lymphocytes. What is the most likely diagnosis?

Accepted Answer

Tubercular meningitis

Answer

Bacterial meningitis

Answer

Partially treated pyogenic infection

Answer

Neurocysticercosis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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