Infectious Diseases — MCQs

Question 1: A 28-year-old woman presented with high-grade fever, cough, diarrhea, and mental confusion for 4 days. Chest X-ray revealed bilateral pneumonitis. What etiology is most likely?

• A. Streptococcus pneumoniae
• B. Staphylococcus aureus
• C. Legionella pneumophila (Correct Answer)
• D. Pseudomonas aeruginosa

Explanation: ### Explanation The clinical presentation of **Legionella pneumophila** (Legionnaires' disease) is classically characterized by a "pneumonia plus" syndrome—respiratory symptoms accompanied by prominent multisystem involvement. **Why Legionella is correct:** 1. **Multisystem Involvement:** Unlike typical bacterial pneumonias, Legionella frequently presents with **extrapulmonary symptoms**. The combination of **high-grade fever**, **diarrhea** (gastrointestinal), and **mental confusion** (neurological) in a patient with pneumonitis is a classic "textbook" description of Legionellosis [1]. 2. **Radiology:** It often presents with bilateral patchy infiltrates or consolidation that may appear worse than the clinical exam suggests. 3. **Laboratory Clue (High-Yield):** Though not mentioned in the stem, **hyponatremia** is a highly specific laboratory finding associated with this pathogen. **Why other options are incorrect:** * **Streptococcus pneumoniae:** The most common cause of community-acquired pneumonia (CAP) [1]. It typically presents with sudden onset chills, productive cough (rusty sputum), and lobar consolidation, but lacks the prominent GI and CNS symptoms seen here. * **Staphylococcus aureus:** Usually follows a viral prodrome (like Influenza) and often leads to necrotizing pneumonia with cavitations or pneumatoceles, rather than multisystem involvement [1]. * **Pseudomonas aeruginosa:** Primarily seen in immunocompromised patients, those with structural lung disease (Cystic Fibrosis, Bronchiectasis), or hospital-acquired settings. It does not typically cause diarrhea or confusion. **NEET-PG Clinical Pearls:** * **Diagnosis:** The most rapid test is the **Urinary Antigen Test** (detects Serogroup 1). The gold standard is culture on **Buffered Charcoal Yeast Extract (BCYE) agar**. * **Treatment:** Macrolides (Azithromycin) or Fluoroquinolones (Levofloxacin). It is inherently resistant to Beta-lactams because it is an intracellular pathogen. * **Transmission:** Associated with contaminated water systems, cooling towers, and air conditioners (no person-to-person spread) [1].

Question 2: A rash appeared 9 hours after a scuba dive. What is the diagnosis?

• A. Decompression sickness (Correct Answer)
• B. Jellyfish envenomation
• C. Mycobacterium marinum infection
• D. Phylum Porifera contact dermatitis

Question 3: Which of the following statements regarding Pneumocystis jirovecii pneumonia (PCP) is/are true? 1. Bronchoscopy with bronchoalveolar lavage (BAL) is the mainstay of diagnosis for PCP. 2. Pneumatoceles are seen in all cases of PCP. 3. A CD4 count < 350 cells/µL is an indication for prophylaxis against PCP. 4. Trimethoprim-sulfamethoxazole is the drug of choice for prophylaxis.

• A. 1 - True, 2 - False, 3 - False, 4 - True (Correct Answer)
• B. 1 - False, 2 - True, 3 - True, 4 - False
• C. 1 - True, 2 - True, 3 - False, 4 - True
• D. 1 - False, 2 - False, 3 - True, 4 - False

Explanation: **Explanation:** **1. Bronchoscopy with BAL is the mainstay of diagnosis (True):** *Pneumocystis jirovecii* cannot be cultured. Diagnosis relies on microscopic visualization of cysts or trophic forms in respiratory specimens [1]. While induced sputum is the initial non-invasive step, **Bronchoalveolar Lavage (BAL)** is the gold standard diagnostic procedure due to its high sensitivity (>90-95%) [1]. **2. Pneumatoceles are seen in all cases (False):** The classic radiological finding in PCP is **bilateral diffuse ground-glass opacities** (perihilar distribution). While pneumatoceles (thin-walled air-filled cysts) can occur and increase the risk of spontaneous pneumothorax, they are seen in only about 10-20% of cases, not all [1]. **3. CD4 count < 350 cells/µL is the indication for prophylaxis (False):** In HIV-infected patients, primary prophylaxis for PCP is indicated when the **CD4 count falls below 200 cells/µL** (or if there is a history of oropharyngeal candidiasis) [1]. A threshold of 350 cells/µL is too high for initiating PCP-specific prophylaxis. **4. Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice (True):** TMP-SMX is the first-line agent for both the **treatment and prophylaxis** of PCP [1]. It is highly effective and also provides cross-protection against Toxoplasmosis. **High-Yield Clinical Pearls for NEET-PG:** * **Stains:** Use **Gomori Methenamine Silver (GMS)** to see crushed-ping-pong-ball shaped cysts or **Giemsa** for trophic forms [1]. * **Biomarker:** Elevated **Serum Beta-D-Glucan** has high sensitivity (negative predictive value) for PCP [2]. * **Steroids:** Indicated in treatment if **PaO2 < 70 mmHg** or Alveolar-arterial (A-a) gradient > 35 mmHg to prevent inflammatory worsening [1]. * **Alternative for Prophylaxis:** Dapsone or Atovaquone (if sulfa-allergic) [1].

Question 4: What is the most likely diagnosis for this 19-month-old girl who presented with a 1-week history of an ascending erythematous eruption?

• A. Cellulitis
• B. Hand, foot, and mouth disease
• C. Herpes zoster (Correct Answer)
• D. Lymphadenitis

Explanation: **Explanation:** The correct diagnosis is **Herpes Zoster (Shingles)**. While commonly associated with the elderly, Herpes Zoster can occur in children, especially those who were infected with Varicella Zoster Virus (VZV) in utero or during the first year of life. The "ascending erythematous eruption" in this clinical scenario refers to a **dermatomal distribution**. Herpes Zoster is caused by the reactivation of latent VZV from the dorsal root ganglia. In pediatric patients, the presentation is often milder than in adults, frequently lacking the classic prodromal pain or post-herpetic neuralgia, which can make the diagnosis challenging if the clinician only expects "adult-type" symptoms. **Why the other options are incorrect:** * **Cellulitis:** This typically presents as a spreading, poorly demarcated area of skin erythema, warmth, and edema. It does not follow a dermatomal pattern and is usually associated with systemic signs like high fever. * **Hand, Foot, and Mouth Disease (HFMD):** Caused by Coxsackievirus A16, this presents with vesicular lesions on the palms, soles, and oral mucosa. It is not dermatomal or "ascending" in a linear nerve distribution. * **Lymphadenitis:** This refers to the inflammation/infection of lymph nodes. While it may cause localized swelling and redness, it does not present as a vesicular or erythematous eruption following a nerve path. **NEET-PG High-Yield Pearls:** * **Risk Factor:** The single greatest risk factor for pediatric Herpes Zoster is **primary varicella infection before age 1**. * **Distribution:** The most common sites in children are the **thoracic** and **lumbar** dermatomes. * **Diagnosis:** Usually clinical; however, the **Tzanck smear** (showing multinucleated giant cells) or PCR are definitive. * **Management:** In healthy children, the condition is often self-limiting; acyclovir is reserved for immunocompromised patients or severe cases.

Question 5: Fever increases water losses by ______ ml/day per degree Celsius?

• A. 100
• B. 200 (Correct Answer)
• C. 400
• D. 800

Explanation: **Explanation:** The correct answer is **200 ml/day per degree Celsius**. **1. Underlying Medical Concept:** In healthy adults, insensible water loss (via skin and lungs) typically accounts for approximately 600–900 ml/day [2]. When a patient develops a fever, the metabolic rate increases (roughly 10–13% for every 1°C rise) [1], leading to increased respiratory rate (tachypnea) and cutaneous vasodilation/diaphoresis. This physiological response significantly accelerates insensible fluid loss. Standard clinical teaching and medical textbooks (such as Harrison’s Principles of Internal Medicine) state that for every degree Celsius rise in body temperature above normal, daily fluid requirements increase by approximately **200 ml/day**. **2. Analysis of Incorrect Options:** * **Option A (100 ml):** This underestimates the physiological demand. While 100 ml might be lost in very mild febrile states, it does not represent the standard clinical calculation used for fluid resuscitation in high-grade fever. * **Option C (400 ml) & D (800 ml):** These values are too high for a single degree Celsius increase. Such volumes are more characteristic of total losses in patients with severe tachypnea, extensive burns, or prolonged high-grade fevers (e.g., 39–40°C) rather than the incremental loss per degree. **3. High-Yield Clinical Pearls for NEET-PG:** * **Metabolic Rate:** For every 1°C rise in temperature, the Basal Metabolic Rate (BMR) increases by approximately **13%** [1]. * **Pediatric Variation:** In children, the rule is often simplified to an additional **10–12%** of maintenance fluids for each degree above 38°C. * **Insensible Loss Components:** Remember that roughly 70% of insensible loss occurs through the skin and 30% through the respiratory tract [2]. Both are exacerbated by fever. * **Clinical Application:** When calculating "Maintenance Fluid" in a febrile patient, always add the incremental loss (200 ml/°C) to the baseline requirement to prevent dehydration.

Question 6: The tourniquet test is used for monitoring patients with which of the following conditions?

• A. Infectious mononucleosis
• B. Zika Virus infection
• C. Dengue fever (Correct Answer)
• D. Chikungunya

Explanation: **Explanation:** The **Tourniquet Test** (Hess test) is a clinical diagnostic tool used to assess **capillary fragility** and is a key component of the WHO criteria for diagnosing **Dengue Fever**. [1] **Why Dengue Fever is correct:** In Dengue, the virus causes increased vascular permeability and thrombocytopenia. The test is performed by inflating a blood pressure cuff to a point midway between the systolic and diastolic pressure for 5 minutes. [1] A positive test is defined as the presence of **≥10 to 20 petechiae per square inch**. It serves as a marker for potential hemorrhagic manifestations and is often positive before the platelet count drops significantly. [1] **Why other options are incorrect:** * **Infectious Mononucleosis:** Caused by EBV; characterized by the triad of fever, pharyngitis, and lymphadenopathy. Diagnosis relies on the Monospot test or atypical lymphocytes on a peripheral smear. * **Zika Virus:** Primarily presents with a maculopapular rash, conjunctivitis, and arthralgia. While it is a Flavivirus like Dengue, capillary fragility is not a hallmark feature. * **Chikungunya:** An Alphavirus characterized by severe, often debilitating polyarthralgia. While it shares the vector (*Aedes*) with Dengue, it does not typically cause the capillary leak syndrome associated with a positive tourniquet test. **Clinical Pearls for NEET-PG:** * **Sensitivity:** The tourniquet test has high specificity but variable sensitivity; a negative test does **not** rule out Dengue. * **Dengue Triad:** High-grade fever, retro-orbital pain, and severe backache ("Break-bone fever"). * **Critical Phase:** Watch for "Warning Signs" (abdominal pain, persistent vomiting, mucosal bleed) which usually occur during the transition from the febrile to the afebrile phase (defervescence). [1]

Question 7: What is the recommended dose of tetanus toxoid to prevent maternal and neonatal tetanus for a pregnant woman whose previous immunization status is not known?

• A. 1 dose
• B. 2 doses (Correct Answer)
• C. 3 doses
• D. 4 doses

Explanation: **Explanation:** The primary goal of tetanus immunization during pregnancy is to prevent maternal tetanus and provide passive immunity to the fetus to prevent neonatal tetanus. **Why Option B is Correct:** According to the National Immunization Schedule (NIS) and WHO guidelines, if a pregnant woman’s immunization status is unknown or she has never been vaccinated, she should receive **two doses** of the tetanus vaccine (currently administered as Tetanus and adult Diphtheria, or **Td** vaccine). * **First Dose:** Administered as early as possible during pregnancy. * **Second Dose:** Administered at least **4 weeks** after the first dose and preferably at least 2 weeks before delivery to ensure adequate antibody transfer. **Why Other Options are Incorrect:** * **Option A (1 dose):** A single dose is insufficient to produce a protective level of antibodies in a previously unimmunized individual. A single "booster" dose is only appropriate if the woman has received at least 2 doses in a pregnancy within the last 3 years. * **Options C & D (3 or 4 doses):** While the full WHO "Life-course" schedule for tetanus involves 5–6 doses for long-term protection, the standard protocol *during a single pregnancy* to ensure immediate protection of the neonate is 2 doses. **High-Yield Clinical Pearls for NEET-PG:** * **The "Booster" Rule:** If a woman becomes pregnant again within **3 years** of receiving two doses, only **one booster dose** (Td) is required. * **Vaccine Type:** The Td vaccine has replaced TT (Tetanus Toxoid) to provide additional protection against adult diphtheria. * **Site/Route:** 0.5 ml, Intramuscular (IM), usually in the upper arm (deltoid). * **Neonatal Tetanus:** Also known as "8th-day disease," it typically presents with trismus (lockjaw) and spasms due to umbilical cord contamination.

Question 8: Which of the following antibiotics is NOT used in the treatment of infectious mononucleosis?

• A. Ampicillin
• B. Gentamycin (Correct Answer)
• C. Erythromycin
• D. Ciprofloxacin

Explanation: Infectious Mononucleosis (IM) is a viral syndrome caused primarily by the **Epstein-Barr Virus (EBV)**. Because it is a viral infection, antibiotics are not used for primary treatment. However, the question focuses on the clinical contraindications and secondary management associated with IM. **Why Gentamycin is the correct answer:** Gentamycin is an aminoglycoside [1]. Unlike the other options, it has no specific clinical relevance or "classic" association with IM. It is neither contraindicated due to specific side effects in IM nor commonly used for the secondary bacterial complications (like streptococcal pharyngitis) that often mimic or coexist with IM. **Analysis of Incorrect Options:** * **Ampicillin (and Amoxicillin):** These are the most high-yield drugs associated with IM. If administered to a patient with IM, they characteristically cause a **maculopapular, pruritic rash** (occurring in ~70-90% of cases). This is an immune-mediated reaction, not a true drug allergy. * **Erythromycin:** This is a macrolide often used as an alternative treatment for secondary streptococcal pharyngitis in IM patients [1], especially if they have a penicillin allergy or to avoid the ampicillin-induced rash. * **Ciprofloxacin:** While not a first-line drug, fluoroquinolones can be used for secondary bacterial infections [1] and do not carry the specific "rash risk" associated with beta-lactams in the context of EBV. **High-Yield Clinical Pearls for NEET-PG:** * **The "Ampicillin Rash":** A classic board favorite. It occurs because EBV causes polyclonal B-cell activation, leading to an altered immune response to certain antibiotics. * **Diagnosis:** Look for the triad of **fever, pharyngitis, and lymphadenopathy** (posterior cervical). * **Laboratory:** Atypical lymphocytes (Downey cells) on peripheral smear and a positive Monospot test (Heterophile antibodies). * **Complication:** Splenic rupture; patients must avoid contact sports for 3–4 weeks.

Question 9: Steroids are indicated in all of the following forms of tuberculosis except?

• A. Meningitis
• B. Pericarditis
• C. Ileocecal tuberculosis (Correct Answer)
• D. Adrenal involvement

Explanation: In the management of Tuberculosis (TB), corticosteroids are used as an adjuvant to Anti-Tubercular Therapy (ATT) to reduce inflammation, prevent fibrosis, and decrease complications in specific closed-space infections. **Why Ileocecal TB is the correct answer:** Steroids are generally **avoided** in intestinal tuberculosis, including ileocecal involvement. The primary concern is that steroids can mask symptoms of perforation or worsen existing ulcerations, potentially leading to secondary bacterial peritonitis. Furthermore, there is no proven benefit of steroids in preventing the most common complication of ileocecal TB, which is intestinal obstruction due to strictures. **Analysis of Incorrect Options:** * **TB Meningitis:** This is the most common indication for steroids. They reduce cerebral edema, decrease intracranial pressure, and prevent basal arachnoiditis, significantly improving survival and neurological outcomes [1]. * **TB Pericarditis:** Steroids are indicated to prevent the progression to constrictive pericarditis and to reduce the need for pericardiectomy by decreasing pericardial fluid accumulation and fibrin deposition [1]. * **Adrenal Involvement (Addison’s Disease):** In TB of the adrenal glands, the tissue is destroyed leading to primary adrenal insufficiency. Steroids (Hydrocortisone/Fludrocortisone) are mandatory as **replacement therapy** to manage the resulting hormonal deficiency [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Steroid Choice:** Dexamethasone or Prednisolone are typically used. * **Other Indications:** Steroids are also used in **Miliary TB** (if there is respiratory distress), **Genitourinary TB** (to prevent ureteric strictures), and **Endobronchial TB** (to prevent bronchostenosis). * **Paradoxical Reactions:** Steroids are the treatment of choice for "IRIS" (Immune Reconstitution Inflammatory Syndrome) in TB-HIV co-infected patients.

Question 10: In Human Immunodeficiency Virus (HIV) infection, diffuse lymphadenopathy in a person who is clinically well is usually a sign of which of the following?

• A. Lymphoma
• B. Kaposi's sarcoma
• C. Tuberculosis
• D. Persistent generalized lymphadenopathy (Correct Answer)

Explanation: The correct answer is **Persistent Generalized Lymphadenopathy (PGL)**. **1. Why PGL is correct:** PGL is defined as enlarged lymph nodes (>1 cm) involving at least two extra-inguinal sites for more than 3 to 6 months, without an obvious underlying cause other than HIV. It is a hallmark of the **early clinical stage (WHO Stage 1)** of HIV infection [1]. Pathologically, it represents follicular hyperplasia in response to the virus. Crucially, patients with PGL are typically **asymptomatic ("clinically well")** except for the lymphadenopathy [1]. **2. Why the other options are incorrect:** * **Lymphoma (A):** While HIV increases the risk of Non-Hodgkin Lymphoma, patients usually present with systemic "B symptoms" (fever, weight loss, night sweats) and rapid nodal growth [2]. It signifies an advanced stage, not a "clinically well" state. * **Kaposi’s Sarcoma (B):** This is an AIDS-defining illness (WHO Stage 4). While it can involve lymph nodes, it primarily presents with characteristic violaceous skin or mucosal lesions. * **Tuberculosis (C):** TB is the most common opportunistic infection in HIV patients in India. However, TB lymphadenitis (Scrofula) usually presents with constitutional symptoms (fever, weight loss), and the nodes are often matted or suppurative, unlike the discrete, non-tender nodes of PGL [2]. **Clinical Pearls for NEET-PG:** * **PGL Node Characteristics:** Typically non-tender, symmetrical, firm, and mobile. Common sites include cervical, axillary, and posterior occipital nodes. * **Biopsy Indication:** Biopsy in PGL is **not** routinely required unless the patient has systemic symptoms, asymmetric nodal enlargement, or nodes that rapidly increase in size [2]. * **WHO Staging:** PGL is classified under **WHO Clinical Stage 1** [1].