Infectious Diseases — MCQs
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What is the cause of the 'bull neck' appearance in Diphtheria?
A 2-month-old infant presents with fever, lethargy, and seizures. The infant was born at term with no significant obstetric or early postnatal complications. Physical examination reveals nuchal rigidity and bulging fontanelles. Lumbar puncture shows a high CSF neutrophil count and gram-positive cocci in chains. What is the most likely causative pathogen?
A 28-year-old woman gave birth to a small for gestational age newborn at 38 weeks of pregnancy. On examination, the newborn was found to have rhinitis, a distended abdomen, wrinkled skin, and palmoplantar blisters. The woman had an earlier history of abortion and stillbirth. What is the most likely diagnosis?
A child is suffering from varicella. When is it earliest and safe for the child to meet her pregnant aunt?
A premature baby of 34 weeks gestation was delivered and developed bullous lesions on the skin. Radiographs show periostitis. What should be the next investigation?
What wavelength is used in the given instrument to treat neonatal pathology?
A 10-year-old boy presents with a two-week history of fever, arthritis, and hepatosplenomegaly. What is the likely diagnosis?
A child presents with fever and maculopapular rash. Which of the following clinical findings is typically NOT associated with measles?
What is the percentage of coincidence between a sore throat and acute rheumatic fever?
What is the standard treatment for Chlamydia pneumoniae infection?
Infectious Diseases Indian Medical PG Practice Questions and MCQs
Question 281: What is the cause of the 'bull neck' appearance in Diphtheria?
- A. Retropharyngeal abscess
- B. Laryngeal edema
- C. Cellulitis
- D. Lymphadenopathy (Correct Answer)
Explanation: **Explanation:** The **'Bull Neck'** appearance is a classic clinical hallmark of **Faucial Diphtheria**, caused by *Corynebacterium diphtheriae*. This characteristic swelling is primarily due to **massive cervical lymphadenopathy** combined with associated **peri-adenitis** and soft tissue edema in the neck. The profound inflammatory response to the diphtheria exotoxin causes the lymph nodes to enlarge significantly, obliterating the angle of the jaw and giving the neck a thickened, "bull-like" contour. **Analysis of Options:** * **A. Retropharyngeal abscess:** While this causes neck swelling and dysphagia, it typically presents with a bulge in the posterior pharyngeal wall and neck stiffness, not the diffuse, symmetrical external "bull neck" seen in diphtheria. * **B. Laryngeal edema:** This occurs in laryngeal diphtheria and leads to stridor and airway obstruction (croup-like symptoms), but it does not manifest as external neck swelling. * **C. Cellulitis:** Although there is soft tissue edema in diphtheria, the primary anatomical driver of the "bull neck" is the underlying lymph node involvement (lymphadenopathy), not a primary bacterial infection of the skin and subcutaneous tissues. **High-Yield Clinical Pearls for NEET-PG:** * **Pseudomembrane:** A greyish-white, tough, leathery membrane that bleeds on attempted removal (due to vascular involvement). * **Schick Test:** Used to determine susceptibility/immunity status to diphtheria. * **Complications:** The exotoxin can cause **Myocarditis** (most common cause of death, usually in the 2nd week) and **Neurological palsies** (e.g., palatal palsy). * **Treatment:** Immediate administration of **Diphtheria Antitoxin (ADS)** is the priority, as it only neutralizes unbound toxin. Antibiotics (Erythromycin or Penicillin) are used to stop toxin production and prevent spread.
Question 282: A 2-month-old infant presents with fever, lethargy, and seizures. The infant was born at term with no significant obstetric or early postnatal complications. Physical examination reveals nuchal rigidity and bulging fontanelles. Lumbar puncture shows a high CSF neutrophil count and gram-positive cocci in chains. What is the most likely causative pathogen?
- A. Coagulase-negative staphylococci
- B. Escherichia coli
- C. Group B Streptococcus (Correct Answer)
- D. Neisseria meningitidis
Explanation: **Explanation:** The clinical presentation of fever, lethargy, seizures, and signs of raised intracranial pressure (bulging fontanelles) in a 2-month-old infant is classic for **Neonatal Meningitis**. **Why Group B Streptococcus (GBS) is correct:** * **Epidemiology:** *Streptococcus agalactiae* (GBS) is the leading cause of neonatal sepsis and meningitis in infants aged 0–3 months. * **Microbiology:** The CSF Gram stain shows **Gram-positive cocci in chains**, which is the characteristic morphology of GBS. * **Clinical Correlation:** Late-onset GBS (occurring between 7 days and 3 months of age) typically presents as meningitis, often acquired from the mother’s vaginal flora or environmental sources. **Why the other options are incorrect:** * **Coagulase-negative staphylococci (CoNS):** These are Gram-positive cocci in **clusters**. They are the most common cause of late-onset sepsis in preterm infants with indwelling central lines, but are rare causes of meningitis in term infants. * **Escherichia coli:** While the second most common cause of neonatal meningitis, it is a **Gram-negative rod**, which contradicts the Gram stain findings. * **Neisseria meningitidis:** This is a **Gram-negative diplococcus**. It is a common cause of meningitis in older children and adolescents, but is less frequent in the early neonatal period. **NEET-PG High-Yield Pearls:** * **Top 3 causes of Neonatal Meningitis:** 1. Group B Streptococcus, 2. *E. coli*, 3. *Listeria monocytogenes*. * **Empiric Treatment:** Ampicillin + Cefotaxime (or Gentamicin). Ampicillin is specifically added to cover *Listeria*. * **Late-onset GBS:** Unlike early-onset, it is not significantly reduced by maternal intrapartum antibiotic prophylaxis.
Question 283: A 28-year-old woman gave birth to a small for gestational age newborn at 38 weeks of pregnancy. On examination, the newborn was found to have rhinitis, a distended abdomen, wrinkled skin, and palmoplantar blisters. The woman had an earlier history of abortion and stillbirth. What is the most likely diagnosis?
- A. Neonatal pemphigus
- B. Scabies
- C. Congenital syphilis (Correct Answer)
- D. Congenital HIV infection
Explanation: ### Explanation The clinical presentation described is classic for **Early Congenital Syphilis** (symptoms appearing before 2 years of age). **Why Congenital Syphilis is correct:** The diagnosis is based on a constellation of pathognomonic findings: * **Rhinitis (Snuffles):** A highly infectious, blood-tinged mucopurulent discharge; often the earliest sign. * **Skin Lesions:** Palmoplantar bullae (Pemphigus syphiliticus) and wrinkled skin (due to intrauterine growth restriction) are characteristic. * **Abdominal Distension:** Typically due to hepatosplenomegaly. * **Obstetric History:** Recurrent abortions and stillbirths are hallmark indicators of untreated maternal syphilis. **Why the other options are incorrect:** * **Neonatal Pemphigus:** This is a rare transient condition caused by the placental transfer of maternal IgG antibodies (Pemphigus vulgaris). It presents with flaccid bullae but lacks systemic features like snuffles or hepatosplenomegaly. * **Scabies:** While it can cause vesicles and pustules in infants (including palms/soles), it does not cause rhinitis, SGA, or the specific obstetric history mentioned. * **Congenital HIV:** Usually asymptomatic at birth. Clinical features like lymphadenopathy and failure to thrive typically develop later in infancy. It does not cause palmoplantar blisters. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad (Late Syphilis):** Interstitial keratitis, Sensorineural hearing loss (8th nerve deafness), and Hutchinson’s teeth (notched incisors). * **Radiological Signs:** Wimberger’s sign (localized erosion of the medial proximal tibia) and periostitis. * **Screening/Diagnosis:** VDRL/RPR for screening; FTA-ABS or TP-PA for confirmation. * **Treatment of Choice:** Aqueous Crystalline Penicillin G.
Question 284: A child is suffering from varicella. When is it earliest and safe for the child to meet her pregnant aunt?
- A. When the lesions have crusted (Correct Answer)
- B. Immediately
- C. Anytime
- D. After the delivery of the baby
Explanation: **Explanation:** The core concept tested here is the **period of infectivity** of the Varicella-Zoster Virus (VZV). **1. Why Option A is Correct:** Varicella (Chickenpox) is highly contagious. The period of communicability extends from **1–2 days before the onset of the rash** until **all lesions have crusted (scabbed) over**. Once the vesicles have dried and formed crusts, the virus is no longer shed from the skin lesions, and the child is no longer infectious. Therefore, it is safe to meet others, especially high-risk individuals like pregnant women, only at this stage. **2. Why Other Options are Incorrect:** * **Options B & C:** These are incorrect because the child is actively shedding the virus through respiratory droplets and vesicular fluid during the pre-eruptive and active vesicle stages. Exposure during this time poses a severe risk of **Congenital Varicella Syndrome** (if in early pregnancy) or **Neonatal Varicella** (if near delivery). * **Option D:** While waiting until after delivery is "safe," it is medically unnecessary. Once the lesions have crusted, the risk of transmission is eliminated, making Option A the earliest safe clinical milestone. **Clinical Pearls for NEET-PG:** * **Incubation Period:** 10–21 days (Average 14–15 days). * **Rash Characteristics:** "Dewdrop on a rose petal" appearance; pleomorphic (all stages of rash seen simultaneously); centripetal distribution. * **Secondary Attack Rate:** Very high (~90%). * **Post-Exposure Prophylaxis:** VariZIG (Varicella Zoster Immune Globulin) should be given to susceptible pregnant women within 10 days of exposure to prevent maternal and fetal complications.
Question 285: A premature baby of 34 weeks gestation was delivered and developed bullous lesions on the skin. Radiographs show periostitis. What should be the next investigation?
- A. VDRL for mother and baby (Correct Answer)
- B. ELISA for HIV
- C. PCR for TB
- D. Hepatitis B surface antigen for mother
Explanation: The clinical presentation of a premature neonate with **bullous skin lesions** (Pemphigus syphiliticus) and **periostitis** is a classic triad for **Congenital Syphilis**. ### **Why Option A is Correct** Congenital syphilis is caused by the transplacental transmission of *Treponema pallidum*. * **Skin Lesions:** The characteristic rash often involves bullae or maculopapular lesions, typically on the palms and soles. * **Radiological Findings:** Bone involvement is seen in 90% of symptomatic infants. **Periostitis** and osteochondritis (e.g., Wimberger’s sign) are hallmark features. * **Diagnosis:** The initial screening step is performing non-treponemal tests (**VDRL or RPR**) on both the mother and the baby. A neonatal titer fourfold higher than the maternal titer is highly suggestive of infection. ### **Why Other Options are Incorrect** * **B (HIV):** While HIV can be transmitted vertically, it typically presents later with failure to thrive, lymphadenopathy, and opportunistic infections, not acute bullous lesions or periostitis. * **C (TB):** Congenital Tuberculosis usually presents with hepatosplenomegaly, respiratory distress, and fever; it does not cause bullous skin disease. * **D (Hepatitis B):** Neonatal Hep-B is usually asymptomatic at birth and is managed with vaccination and HBIG; it does not present with skeletal or dermatological abnormalities. ### **NEET-PG High-Yield Pearls** * **Early Congenital Syphilis (<2 years):** Presents with snuffles (hemorrhagic rhinitis), palmoplantar rash, and pseudoparalysis of Parrot (due to painful bone lesions). * **Late Congenital Syphilis (>2 years):** Hutchinson’s triad (interstitial keratitis, sensorineural deafness, and Hutchinson’s teeth), Mulberry molars, and Sabre shin. * **Treatment of Choice:** Intravenous **Penicillin G** for 10 days.
Question 286: What wavelength is used in the given instrument to treat neonatal pathology?
- A. 360 nm
- B. 470 nm (Correct Answer)
- C. 540 nm
- D. 230 nm
Explanation: ***470 nm*** - This wavelength falls within the **therapeutic blue light range** (450-490 nm) used in **phototherapy units** for treating neonatal jaundice. - **Blue light** at this wavelength effectively converts **unconjugated bilirubin** to water-soluble photoisomers that can be excreted without conjugation. *360 nm* - This wavelength represents **UV-A light**, which is outside the therapeutic range for **neonatal phototherapy**. - **UV light** can cause skin damage and is not used for treating **neonatal hyperbilirubinemia**. *540 nm* - This wavelength corresponds to **green light**, which is less effective than blue light for **bilirubin photoisomerization**. - **Green light** has minimal therapeutic benefit and is not the standard wavelength used in **phototherapy units**. *230 nm* - This wavelength represents **far UV-C light**, which is highly dangerous and can cause severe **DNA damage** and skin burns. - **Far UV light** has no therapeutic role in neonatal care and would be harmful to newborns.
Question 287: A 10-year-old boy presents with a two-week history of fever, arthritis, and hepatosplenomegaly. What is the likely diagnosis?
- A. Systemic onset Juvenile Idiopathic Arthritis (Correct Answer)
- B. Acute Leukemia
- C. Enteric fever
- D. Measles
Explanation: ### Explanation **Systemic onset Juvenile Idiopathic Arthritis (soJIA)**, formerly known as Still’s disease, is the most likely diagnosis. The classic triad of **prolonged fever, arthritis, and hepatosplenomegaly** (part of the reticuloendothelial involvement) is hallmark for this condition. The fever in soJIA is typically "quotidian" (spiking once or twice daily to >39°C and returning to baseline). Other common features include an evanescent, salmon-pink macular rash and lymphadenopathy. **Why other options are incorrect:** * **Acute Leukemia:** While it can present with fever, bone pain, and organomegaly, the "arthritis" in leukemia is usually severe bone pain rather than true joint swelling. A peripheral smear showing blasts would be diagnostic. * **Enteric Fever:** Presents with step-ladder fever and hepatosplenomegaly, but **arthritis is rare**. It typically features gastrointestinal symptoms and a relative bradycardia (Faget’s sign). * **Measles:** This is an acute viral illness characterized by the 3 C’s (Cough, Coryza, Conjunctivitis), Koplik spots, and a maculopapular rash. It does not cause chronic arthritis or significant hepatosplenomegaly over two weeks. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Criteria:** Fever for at least 2 weeks (with daily spikes for 3 days) plus arthritis in one or more joints. * **Laboratory Findings:** Marked leukocytosis (neutrophilia), thrombocytosis, and highly elevated ESR/CRP. * **Complication:** **Macrophage Activation Syndrome (MAS)** is a life-threatening complication of soJIA, characterized by a sudden drop in ESR and platelets with a paradoxical rise in Ferritin. * **Treatment:** NSAIDs are first-line; Biologics (IL-1 and IL-6 inhibitors like Anakinra or Tocilizumab) are used for refractory cases.
Question 288: A child presents with fever and maculopapular rash. Which of the following clinical findings is typically NOT associated with measles?
- A. Pneumonia
- B. Otitis media (Correct Answer)
- C. Koplik spots
- D. Encephalitis
Explanation: **Explanation:** The question asks for the finding **NOT** typically associated with measles. However, there is a common clinical misconception here. In standard medical literature and NEET-PG patterns, **Otitis Media is actually the most common complication of Measles.** If the question implies which finding is "not typically associated" in terms of being a *pathognomonic* sign or a *rare* occurrence, the options must be weighed by frequency versus specificity. 1. **Why Otitis Media is the "Correct" Answer (Contextual):** In some specific exam frames, if the question asks for the most common cause of *mortality*, the answer is Pneumonia. If it asks for a *pathognomonic* sign, it is Koplik spots. If the key identifies Otitis Media as "not associated," it is likely a distractor or referring to the fact that it is a secondary bacterial infection rather than a direct viral manifestation, though this is clinically debatable as it occurs in ~7-10% of cases. 2. **Analysis of Other Options:** * **Koplik Spots:** These are pathognomonic (diagnostic) for measles, appearing on the buccal mucosa opposite the lower second molars 1-2 days before the rash. * **Pneumonia:** This is the **most common cause of death** associated with measles in children. * **Encephalitis:** A serious neurological complication. Acute post-infectious encephalitis occurs in 1 in 1,000 cases. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication:** Otitis Media. * **Most common cause of death:** Pneumonia (Hecht’s Giant Cell Pneumonia). * **Pathognomonic sign:** Koplik Spots. * **Vitamin Supplementation:** Vitamin A (reduces morbidity/mortality). * **Late complication:** SSPE (Subacute Sclerosing Panencephalitis) occurs 7-10 years later. * **First sign to appear:** Fever (Prodromal stage).
Question 289: What is the percentage of coincidence between a sore throat and acute rheumatic fever?
- A. 3% (Correct Answer)
- B. 5%
- C. 7%
- D. 9%
Explanation: **Explanation:** Acute Rheumatic Fever (ARF) is a delayed, non-suppurative sequela of an upper respiratory tract infection caused by **Group A Beta-Hemolytic Streptococcus (GABHS)**. The relationship between the initial infection and the development of ARF is a classic high-yield concept in Pediatrics. **1. Why 3% is Correct:** Epidemiological studies have established that in an **untreated** or inadequately treated episode of GABHS pharyngitis (sore throat), approximately **3%** of individuals will go on to develop Acute Rheumatic Fever. This percentage remains the gold standard in medical literature for endemic populations. In contrast, during "sporadic" outbreaks in developed nations, the incidence may drop significantly below 1%, but for examination purposes, the 3% rule is the recognized benchmark. **2. Analysis of Incorrect Options:** * **5%, 7%, and 9%:** These values overestimate the attack rate. While GABHS is a common cause of sore throat, the progression to ARF requires a specific combination of host genetic susceptibility and the rheumatogenic potential of the specific streptococcal strain (e.g., M-types 1, 3, 5, 6, 18). **3. Clinical Pearls for NEET-PG:** * **The Latent Period:** ARF typically develops **2–4 weeks** after the initial sore throat. * **Prevention:** Primary prevention (treating the sore throat with Penicillin within 9 days of onset) can almost entirely prevent the development of ARF. * **Skin Infections:** Unlike Post-Streptococcal Glomerulonephritis (PSGN), **ARF does not follow streptococcal skin infections (impetigo/pyoderma).** It only follows pharyngeal infections. * **Diagnosis:** Diagnosis is clinical, based on the **Revised Jones Criteria (2015)**, which now categorizes patients into low-risk and moderate/high-risk populations.
Question 290: What is the standard treatment for Chlamydia pneumoniae infection?
- A. Erythromycin (Correct Answer)
- B. Ceftriaxone
- C. Penicillin
- D. Sulphonamide
Explanation: **Explanation:** *Chlamydia pneumoniae* is an obligate intracellular bacterium and a common cause of atypical pneumonia in children and adolescents. Because it lacks a traditional peptidoglycan cell wall, it is inherently resistant to beta-lactam antibiotics. **Why Erythromycin is correct:** Macrolides, such as **Erythromycin**, are the treatment of choice for *Chlamydia* species. They work by inhibiting protein synthesis by binding to the 50S ribosomal subunit. In pediatric practice, while Erythromycin is the classic answer, newer macrolides like Azithromycin or Clarithromycin are often preferred due to better GI tolerance and simpler dosing schedules. For older children (>8 years), Tetracyclines (Doxycycline) are also an effective alternative. **Why the other options are incorrect:** * **Ceftriaxone (Cephalosporin) & Penicillin:** These are beta-lactam antibiotics that act by inhibiting cell wall synthesis. Since *Chlamydia* does not have a typical bacterial cell wall, these drugs are completely ineffective. * **Sulphonamides:** While sulfonamides interfere with folic acid synthesis and are used for some intracellular organisms (like *Nocardia*), they are not the standard of care for *Chlamydia pneumoniae* and show poor clinical efficacy compared to macrolides. **High-Yield Clinical Pearls for NEET-PG:** * **Atypical Presentation:** Look for a "subacute" onset with a prominent, non-productive cough, low-grade fever, and "dissociation" (physical signs on chest X-ray are much worse than the clinical appearance of the patient). * **Chlamydia trachomatis (Infants):** Causes "staccato cough" and peripheral eosinophilia in neonates (usually 2–12 weeks old). Erythromycin is also the drug of choice here. * **Drug Side Effect:** Be aware that Erythromycin use in neonates is associated with an increased risk of **Infantile Hypertrophic Pyloric Stenosis (IHPS)**.
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Vaccine-Preventable Diseases
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Immunization Schedule
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Common Childhood Infections
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Pediatric HIV
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Congenital Infections
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Fever in Infants and Children
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Meningitis and Encephalitis
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Respiratory Tract Infections
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Gastrointestinal Infections
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Parasitic Infections
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Tuberculosis in Children
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Opportunistic Infections
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