Infectious Diseases — MCQs

A 29-year-old man presents with fever, myalgia, headache, nausea, and a rash on his wrists, ankles, and body after a hiking trip where he experienced numerous insect bites. Examination reveals a blood pressure of 90/60 mmHg, pulse of 100/min, and respirations of 20/min. He has multiple macules, some with hemorrhagic centers consistent with petechiae. A clinical diagnosis of Rocky Mountain Spotted Fever (RMSF) is made. What is the most common central nervous system (CNS) presentation in this condition?

Q526Medium

A young female presents with myalgia, fever, headache, diarrhea, and an erythematous rash which first appeared in the groin. What is the most likely diagnosis?

Q527Medium

Migratory necrolytic erythema is seen in which of the following conditions?

Q528Medium

Which of the following is NOT seen in Mycoplasma pneumoniae infections?

Q529Medium

A patient is found to be HIV positive on routine check-up. They have no symptoms and a CD4 count of 800 cells/mm³. What is the recommended management for this patient?

Q530Easy

All of the following features are seen in dengue hemorrhagic fever except?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 521: Which of the following is NOT typically seen in Dengue fever?

A. Hemorrhagic tendencies
B. High grade fever
C. Circulatory problems
D. Hepato-splenomegaly (Correct Answer)

Explanation: ### Explanation In Dengue fever, the hallmark clinical features are related to capillary leak and bone marrow suppression. While **Hepatomegaly** (enlargement of the liver) is a common finding and a recognized "warning sign" in Dengue Hemorrhagic Fever (DHF), **Splenomegaly is rare**. The presence of significant hepato-splenomegaly should prompt a clinician to consider alternative diagnoses such as Malaria, Enteric fever, or Kala-azar. **Analysis of Options:** * **A. Hemorrhagic tendencies:** These are common due to thrombocytopenia and vascular dysfunction. Manifestations include petechiae, ecchymosis, and mucosal bleeding (e.g., epistaxis) [1]. * **B. High grade fever:** Dengue typically presents with a sudden-onset, high-grade fever (often "saddleback" or biphasic) accompanied by retro-orbital pain and severe myalgia ("break-bone fever") [1]. * **C. Circulatory problems:** Plasma leakage due to increased capillary permeability can lead to hemoconcentration, pleural effusion, ascites, and in severe cases, Dengue Shock Syndrome (DSS) [1]. * **D. Hepato-splenomegaly:** As noted, while the liver is often tender and enlarged, the spleen is typically not involved. **Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Day biter; breeds in clean stagnant water). * **Warning Signs:** Abdominal pain, persistent vomiting, mucosal bleed, lethargy, and **Hepatomegaly >2 cm**. * **Lab Findings:** Leukopenia (early sign), Thrombocytopenia, and rising Hematocrit (indicates plasma leak). * **Tourniquet Test:** Positive if >10–20 petechiae per square inch; used as a screening tool for capillary fragility [1]. * **NS1 Antigen:** Best for early diagnosis (Days 1–5). IgM/IgG ELISA is used after Day 5.

Question 522: Which vaccine is contraindicated in patients with AIDS?

A. DPT
B. BCG (Correct Answer)
C. Rabies
D. Measles

Explanation: **Explanation:** The core medical principle here is the distinction between **Live Attenuated Vaccines (LAVs)** and **Inactivated/Toxoid vaccines** in the context of immunocompromised states [1]. **Why BCG is the correct answer:** BCG (Bacillus Calmette-Guérin) is a live attenuated vaccine derived from *Mycobacterium bovis*. In patients with AIDS (CD4 count <200 cells/mm³ or symptomatic HIV), the immune system cannot contain even the weakened vaccine strain. This can lead to **disseminated BCG infection** (BCG-osis), which is often fatal. According to WHO and National AIDS Control Organisation (NACO) guidelines, BCG is strictly contraindicated in symptomatic HIV/AIDS patients. **Analysis of Incorrect Options:** * **A. DPT:** This is a combination of toxoids (Diphtheria, Tetanus) and killed/subunit components (Pertussis). Since it contains no live organisms, it cannot cause disease and is safe for HIV patients. * **C. Rabies:** This is a killed (inactivated) vaccine. It is safe and mandatory for post-exposure prophylaxis in HIV patients, although the antibody response may be lower than in healthy individuals. * **D. Measles:** While Measles is a live vaccine, it is a **notable exception**. In HIV-infected children who are *not* severely immunocompromised, the risk of lethal natural measles outweighs the risk of the vaccine. However, in the context of full-blown **AIDS**, BCG is considered more dangerous and is the primary contraindication among the choices. **High-Yield Clinical Pearls for NEET-PG:** * **General Rule:** Live vaccines (BCG, Yellow Fever, MMR, Varicella, Oral Polio, Ty21a) are generally contraindicated in severely immunocompromised states [1]. * **The CD4 Threshold:** Most live vaccines are avoided if the CD4 count is **<200 cells/mm³**. * **Exception:** MMR and Varicella vaccines can be considered in HIV-infected children if the CD4 percentage is **>15%**. * **Yellow Fever:** This is the most strictly contraindicated live vaccine for HIV patients traveling to endemic zones if their CD4 count is low.

Question 523: What constitutes a complicated urinary tract infection (UTI)?

A. A urinary tract infection in the absence of underlying renal or neurological disease.
B. A urinary tract infection that occurs in the presence of underlying structural, medical, or neurological disease. (Correct Answer)
C. More than three symptomatic urinary tract infections within 12 months, despite clinical therapy.
D. Recurrent urinary tract infections caused by a different pathogen at any time.

Explanation: ### Explanation **1. Understanding the Correct Answer (Option B)** A **Complicated UTI** is defined by the presence of factors that increase the risk of treatment failure, serious complications, or infection by resistant organisms. These factors include **structural abnormalities** (e.g., kidney stones, prostatic hypertrophy, vesicoureteral reflux), **medical comorbidities** (e.g., Diabetes Mellitus, pregnancy, immunosuppression), or **neurological diseases** (e.g., neurogenic bladder) [1]. Essentially, any condition that impairs the host's defense mechanisms or interferes with the free flow of urine classifies the UTI as complicated. **2. Analysis of Incorrect Options** * **Option A:** This describes an **Uncomplicated UTI**, typically seen in healthy, non-pregnant, premenopausal women with anatomically normal urinary tracts. * **Option C:** This is the definition of **Recurrent UTI** (specifically, $\geq 3$ episodes in 12 months or $\geq 2$ episodes in 6 months). While recurrent UTIs can be complicated, the frequency alone does not define "complicated" status [1]. * **Option D:** This describes **Reinfection**, which is a type of recurrent UTI caused by a different organism. If the same organism causes a repeat infection within 2 weeks of treatment, it is termed **Relapse**. **3. NEET-PG High-Yield Pearls** * **Gender Rule:** UTIs in **males** are almost always considered **complicated** due to the anatomical length of the urethra and potential prostatic involvement. * **Common Pathogens:** While *E. coli* is the most common cause of both types, complicated UTIs have a higher prevalence of *Proteus*, *Klebsiella*, *Pseudomonas*, and *Enterococcus*. * **Management:** Uncomplicated UTIs are treated with short courses (3–5 days), whereas complicated UTIs require longer therapy (7–14 days) and often necessitate imaging (USG/CT) to rule out abscesses or obstructions [1].

Question 524: A 20-year-old male presents with fever, fatigue, posterior cervical lymphadenopathy, palatal petechiae, and splenomegaly. Peripheral smear shows atypical lymphocytes and the heterophile antibody is positive. What is the likely diagnosis?

A. Acute leukemia
B. Lymphocytic leukemia
C. Infectious mononucleosis (Correct Answer)
D. Chronic myeloid leukemia

Explanation: ### Explanation **Correct Answer: C. Infectious Mononucleosis (IM)** **Reasoning:** The clinical triad of **fever, pharyngitis, and lymphadenopathy** (classically posterior cervical) is hallmark for Infectious Mononucleosis, caused by the **Epstein-Barr Virus (EBV)** [2]. * **Palatal petechiae** and **splenomegaly** are highly specific physical findings [3]. * The laboratory diagnosis is confirmed by the presence of **atypical lymphocytes** (Downey cells)—which are actually activated T-cells—and a **positive Heterophile antibody test** (Monospot test), which detects IgM antibodies that agglutinate sheep or horse red blood cells [1]. **Why Incorrect Options are Wrong:** * **A & B (Acute/Lymphocytic Leukemia):** While leukemia can present with lymphadenopathy and splenomegaly, the presence of a positive heterophile antibody is pathognomonic for IM. Furthermore, leukemia would typically show "blasts" on a smear rather than reactive atypical lymphocytes, along with cytopenias (anemia/thrombocytopenia). * **D (Chronic Myeloid Leukemia):** CML typically presents in older adults with massive splenomegaly and a "leukemoid" blood picture (predominance of neutrophils, myelocytes, and metamyelocytes) with a low LAP score [3], not fever and pharyngitis in a young adult. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Ampicillin Rash":** If a patient with IM is mistakenly treated with Ampicillin or Amoxicillin for suspected strep throat, they often develop a characteristic maculopapular rash. 2. **Splenic Rupture:** This is a rare but life-threatening complication; patients must avoid contact sports for 3–4 weeks. 3. **Diagnosis:** Monospot test may be false-negative in the first week of illness or in children <4 years old. 4. **Atypical Lymphocytes:** These are **CD8+ T-cells** reacting against EBV-infected B-cells [1].

Question 525: A 29-year-old man presents with fever, myalgia, headache, nausea, and a rash on his wrists, ankles, and body after a hiking trip where he experienced numerous insect bites. Examination reveals a blood pressure of 90/60 mmHg, pulse of 100/min, and respirations of 20/min. He has multiple macules, some with hemorrhagic centers consistent with petechiae. A clinical diagnosis of Rocky Mountain Spotted Fever (RMSF) is made. What is the most common central nervous system (CNS) presentation in this condition?

A. Hemiplegia
B. Cranial nerve abnormalities
C. Paraplegia
D. Encephalitis (Correct Answer)

Explanation: **Explanation:** **Rocky Mountain Spotted Fever (RMSF)**, caused by *Rickettsia rickettsii*, is a systemic vasculitis. The pathogen infects the vascular endothelial cells, leading to increased capillary permeability, microvascular leakage, and inflammatory responses across various organ systems, including the Central Nervous System (CNS) [2]. **1. Why Encephalitis is Correct:** CNS involvement is a hallmark of severe RMSF due to widespread microvascular injury in the brain. **Encephalitis** is the most common CNS manifestation, presenting as altered mental status, confusion, lethargy, or even coma. It occurs in approximately 25–35% of patients. Pathologically, this is characterized by "typhus nodules" (glial nodules) and perivascular mononuclear infiltration. [2] **2. Why Incorrect Options are Wrong:** * **A & C (Hemiplegia/Paraplegia):** While focal neurological deficits can occur due to localized vasculitis or stroke-like events, they are much less common than global cerebral dysfunction (encephalitis). * **B (Cranial nerve abnormalities):** These are rare complications (e.g., deafness or ocular palsies) and do not represent the primary or most frequent CNS presentation compared to the diffuse involvement seen in encephalitis. **3. Clinical Pearls for NEET-PG:** * **The Classic Triad:** Fever, headache, and a centripetal rash (starts on wrists/ankles and spreads to the trunk) [1]. * **The Rash:** Typically appears on day 3–5; it starts as maculopapular and often becomes **petechial** (a sign of severe microvascular damage). * **Treatment:** **Doxycycline** is the drug of choice for all ages, including children, as the benefit of treating this potentially fatal disease outweighs the risk of dental staining. * **Laboratory findings:** Look for hyponatremia and thrombocytopenia in the clinical vignette.

Question 526: A young female presents with myalgia, fever, headache, diarrhea, and an erythematous rash which first appeared in the groin. What is the most likely diagnosis?

A. Toxic epidermal necrolysis
B. Staphylococcal scalded skin syndrome
C. Toxic shock syndrome (Correct Answer)
D. Epidermolysis bullosa

Explanation: ### Explanation **Toxic Shock Syndrome (TSS)** is the correct diagnosis based on the clinical constellation of high fever, multisystem involvement (myalgia, diarrhea, headache), and a characteristic rash. [1] **1. Why Toxic Shock Syndrome is correct:** TSS is caused by **TSST-1**, a superantigen produced by *Staphylococcus aureus*. This toxin causes massive non-specific T-cell activation and a "cytokine storm." [2] * **The Rash:** It typically presents as a diffuse, blanching, sun-burn-like erythroderma. A high-yield clinical sign is that the rash often **starts in the groin or axilla** before generalizing. * **Systemic Symptoms:** The involvement of the GI tract (diarrhea) and muscles (myalgia/elevated CPK) are classic diagnostic criteria. It is often associated with tampon use or infected surgical wounds. **2. Why other options are incorrect:** * **Toxic Epidermal Necrolysis (TEN):** This is a severe drug reaction characterized by extensive skin detachment (Nikolsky sign positive) involving >30% of the body surface. It lacks the specific prodrome of TSS. * **Staphylococcal Scalded Skin Syndrome (SSSS):** Caused by exfoliative toxins (ETA/ETB). While it features erythema, it primarily affects neonates/children and results in superficial blistering and skin peeling, usually sparing the mucous membranes and lacking the profound multisystem shock seen in TSS. * **Epidermolysis Bullosa:** This is a group of genetic mechanobullous disorders characterized by skin fragility and blistering in response to minor trauma; it is not an acute febrile infectious process. **High-Yield Pearls for NEET-PG:** * **Diagnostic Hallmark:** Desquamation (peeling) of the palms and soles typically occurs **1–2 weeks after** the onset of the illness. [2] * **Criteria:** Must include Fever (>38.9°C), Hypotension, Rash, and involvement of ≥3 organ systems. * **Management:** Aggressive fluid resuscitation, removal of the source (e.g., tampon), and antibiotics (Clindamycin is often added to inhibit toxin production).

Question 527: Migratory necrolytic erythema is seen in which of the following conditions?

A. Glucagonoma syndrome (Correct Answer)
B. Peutz-Jeghers syndrome
C. Sarcoidosis
D. Amyloidosis

Explanation: **Explanation:** **Migratory Necrolytic Erythema (MNE)** is a pathognomonic cutaneous marker for **Glucagonoma**, a rare alpha-cell tumor of the pancreas. The rash typically presents as pruritic, painful, erythematous plaques that progress to vesicles and bullae, eventually crusting and healing with hyperpigmentation. It most commonly affects the perineum, buttocks, and distal extremities. The underlying mechanism is thought to be related to hypoaminoacidemia, zinc deficiency, or the direct effect of excess glucagon causing inflammatory arachidonic acid release. **Analysis of Incorrect Options:** * **Peutz-Jeghers Syndrome:** Characterized by hamartomatous gastrointestinal polyps and **mucocutaneous hyperpigmentation** (melanotic macules) on the lips, buccal mucosa, and digits. * **Sarcoidosis:** Associated with various skin manifestations, most notably **Lupus Pernio** (violaceous plaques on the nose/cheeks) and **Erythema Nodosum** (painful pretibial nodules). * **Amyloidosis:** Classic skin findings include **"Pinch purpura"** (periorbital ecchymosis) and waxy, translucent papules or plaques due to amyloid deposition in the dermis. **High-Yield Clinical Pearls for NEET-PG:** * **Glucagonoma Syndrome (The 4 D's):** **D**ermatitis (MNE), **D**iabetes (mild), **D**epression, and **D**eep Vein Thrombosis (DVT). * **Laboratory findings:** Extremely high serum glucagon levels (>1000 pg/mL) and low serum amino acids. * **Treatment:** Somatostatin analogues (Octreotide) are used to control symptoms by inhibiting glucagon release before surgical resection.

Question 528: Which of the following is NOT seen in Mycoplasma pneumoniae infections?

A. Diffuse infiltration of lungs
B. Cannot be cultured routinely
C. Best treated by cefotaxime (Correct Answer)
D. Serology is useful in diagnosis

Explanation: **Explanation:** The correct answer is **C (Best treated by cefotaxime)** because *Mycoplasma pneumoniae* is a "cell wall-deficient" bacterium. Since it lacks a peptidoglycan cell wall, it is inherently resistant to beta-lactam antibiotics like cephalosporins (e.g., cefotaxime) and penicillins, which act by inhibiting cell wall synthesis. The drugs of choice are protein synthesis inhibitors such as **Macrolides** (Azithromycin), Tetracyclines (Doxycycline), or Fluoroquinolones. **Analysis of other options:** * **A. Diffuse infiltration of lungs:** Characteristically, *Mycoplasma* causes "Atypical Pneumonia." Clinical symptoms are often mild ("walking pneumonia"), but chest X-rays show disproportionately extensive interstitial or diffuse infiltrates, often described as a "patchy" or "ground-glass" appearance. * **B. Cannot be cultured routinely:** *Mycoplasma* is extremely fastidious, requires specialized media (e.g., PPLO agar/Eaton’s agar), and grows very slowly (2–3 weeks). Therefore, culture is not used for routine clinical diagnosis. * **D. Serology is useful in diagnosis:** Since culture is impractical, diagnosis relies on serology (detecting IgM antibodies) or PCR. Historically, the **Cold Agglutinin test** (IgM against I-antigen on RBCs) was used, though it is non-specific. **NEET-PG High-Yield Pearls:** * **Appearance on Culture:** "Fried egg" colonies. * **Extrapulmonary Manifestations:** Bullous myringitis (ear pain), Stevens-Johnson Syndrome, and autoimmune hemolytic anemia (due to cold agglutinins). * **Smallest free-living organism:** It contains both DNA and RNA but lacks a cell wall.

Question 529: A patient is found to be HIV positive on routine check-up. They have no symptoms and a CD4 count of 800 cells/mm³. What is the recommended management for this patient?

A. No treatment is required.
B. Zidovudine plus stavudine for 28 days.
C. Tenofovir plus lamivudine plus efavirenz for lifelong treatment. (Correct Answer)
D. Tenofovir plus zidovudine plus lamivudine for lifelong treatment.

Explanation: ### Explanation **1. Why Option C is Correct:** The management of HIV has shifted from "wait and watch" to the **"Test and Treat" policy**. According to current WHO and NACO guidelines, Antiretroviral Therapy (ART) should be initiated in **all** individuals living with HIV, regardless of their clinical stage or CD4 cell count [1]. Even with a high CD4 count (800 cells/mm³), early initiation reduces morbidity, mortality, and the risk of transmission (Treatment as Prevention). The standard first-line regimen (TLE) consists of two Nucleoside Reverse Transcriptase Inhibitors (NRTIs) and one Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI): **Tenofovir (TDF) + Lamivudine (3TC) + Efavirenz (EFV)** [1]. *(Note: While Dolutegravir-based regimens (TLD) are now the preferred first-line globally, TLE remains a standard academic answer for NEET-PG based on established NACO protocols.)* **2. Why Other Options are Wrong:** * **Option A:** Incorrect because the "Test and Treat" strategy mandates treatment for all HIV-positive patients to prevent reservoir expansion and transmission. * **Option B:** Incorrect. Zidovudine and Stavudine are both thymidine analogues; using them together is **contraindicated** due to competitive antagonism. Furthermore, 28 days is the duration for Post-Exposure Prophylaxis (PEP), not definitive treatment. * **Option D:** Incorrect. This regimen uses three NRTIs. Standard ART requires a combination of different classes (usually 2 NRTIs + 1 NNRTI/Integrase Inhibitor/PI) to prevent drug resistance [1]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Preferred First-line (NACO):** TDF (300mg) + 3TC (300mg) + DTG (50mg) is the current transition (TLD), but TLE is the traditional gold standard for exams. * **CD4 Monitoring:** Once ART starts, CD4 count is typically monitored every 6 months initially, then annually if stable. * **Viral Load:** The most sensitive indicator of ART response; "Undetectable = Untransmittable" (U=U). * **Pregnancy:** ART is started immediately in all pregnant/breastfeeding women regardless of CD4 count to prevent vertical transmission. [1]

Question 530: All of the following features are seen in dengue hemorrhagic fever except?

A. Positive tourniquet test
B. Platelet counts less than 1 lac
C. Falling hematocrit value (Correct Answer)
D. Acute onset of high fever

Explanation: In Dengue Hemorrhagic Fever (DHF), the hallmark pathophysiological change is **increased vascular permeability**, leading to plasma leakage. This results in **hemoconcentration**, which manifests as a **rising hematocrit (≥20% increase from baseline)**, not a falling one. A falling hematocrit is typically seen only after significant clinical hemorrhage or during the recovery phase (due to hemodilution). ### Analysis of Options: * **Option C (Correct):** Falling hematocrit is the "except" because DHF is characterized by plasma escaping the intravascular space, causing the blood to become more concentrated (rising hematocrit). * **Option A:** A **Positive Tourniquet Test** (≥10–20 petechiae per square inch) is a classic sign of capillary fragility and is one of the diagnostic criteria for DHF [1]. * **Option B:** **Thrombocytopenia** (platelet count <100,000 cells/mm³) is a mandatory WHO criterion for the diagnosis of DHF [1]. * **Option D:** Like Dengue Fever, DHF begins with an **acute onset of high-grade fever**, usually lasting 2–7 days [1]. ### NEET-PG High-Yield Pearls: * **WHO Criteria for DHF:** 1) Fever, 2) Hemorrhagic manifestations (e.g., positive tourniquet test), 3) Thrombocytopenia (<1 lac), and 4) Evidence of plasma leakage (rising hematocrit, pleural effusion, or ascites). * **Critical Phase:** Occurs around the time of **defervescence** (when fever drops). This is when the risk of Shock (Dengue Shock Syndrome) is highest [1]. * **Grading:** DHF is graded I to IV. Grades III and IV are classified as Dengue Shock Syndrome (DSS). * **Most sensitive indicator of plasma leakage:** A rising hematocrit.

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Viral Infections (Hepatitis, Herpes, etc.)

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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