Infectious Diseases — MCQs

A 5-year-old girl presents with a several-day history of localized swelling in the right side of her neck. There is no recent history of sore throat. Physical examination reveals a low-grade fever and one very tender, firm, slightly enlarged lymph node in the right cervical region. A CBC shows mild leukocytosis, and fine needle aspiration of the lymph node reveals scattered neutrophils. Which of the following is the most likely diagnosis?

Q246Easy

What virus can cause Roseola infantum?

Q247Easy

Which of the following is NOT a feature of congenital rubella syndrome?

Q248Medium

Which of the following statements is/are true about meningitis?

Q249Easy

What is the recommended single dose of Albendazole for a 10-year-old child being treated for roundworm infestation?

Q250Medium

A 1 and 1/2 year old child with a history of chronic diarrhea presents with perioral and perineal rash. What is your diagnosis?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 241: A 3-year-old boy presents with a 1-day history of loose stools, fever, abdominal cramping, headache, and myalgia. He has no blood in the stool. A careful history reveals that he has several pet turtles. Which of the following is most likely the causative agent of his diarrhea?

A. Chlamydia psittaci
B. Entamoeba histolytica
C. Salmonella spp (Correct Answer)
D. Staphylococcus aureus

Explanation: ### **Explanation** **Correct Answer: C. Salmonella spp** The clinical presentation of fever, abdominal cramps, and diarrhea following contact with **pet turtles** is a classic association for **Nontyphoidal Salmonella (NTS)**. * **Underlying Concept:** Reptiles (turtles, lizards, snakes) and amphibians are natural reservoirs for *Salmonella*. They shed the bacteria in their feces, which can contaminate their skin, shells, and habitat water. In children, especially those under 5 years, this often leads to self-limiting gastroenteritis characterized by nausea, vomiting, abdominal cramps, and non-bloody diarrhea. --- ### **Why Other Options are Incorrect:** * **A. Chlamydia psittaci:** This is associated with **birds** (parrots, pigeons). It typically causes **Psittacosis**, which presents as atypical pneumonia and systemic symptoms, not primary gastroenteritis. * **B. Entamoeba histolytica:** While it causes diarrhea and abdominal pain, it is usually associated with contaminated food/water in endemic areas and often presents as **bloody diarrhea** (amoebic dysentery) with flask-shaped ulcers on colonoscopy. It has no association with reptiles. * **D. Staphylococcus aureus:** This causes **food poisoning** via preformed enterotoxins. It has a very rapid onset (1–6 hours) and is typically associated with mayonnaise, dairy, or processed meats, not animal contact. --- ### **NEET-PG High-Yield Pearls:** * **Reptile-Associated Salmonellosis:** Turtles are such a high-risk source that the sale of small turtles (<4 inches) was banned in the US to prevent pediatric outbreaks. * **Salmonella vs. Shigella:** Salmonella typically involves the ileum/colon and may or may not be bloody; Shigella is more likely to cause high fever, seizures (due to neurotoxins), and early bloody mucoid stools. * **Treatment:** In healthy children >2 years with NTS gastroenteritis, antibiotics are generally **avoided** as they do not shorten the illness and may prolong the carrier state. Antibiotics (Ceftriaxone or Azithromycin) are reserved for infants <3 months or those with systemic features.

Question 242: Which of the following drugs are used in the first-line treatment of tuberculosis in children?

A. Streptomycin
B. Pyrazinamide
C. Ethionamide
D. Streptomycin and Pyrazinamide (Correct Answer)

Explanation: **Explanation:** The standard first-line treatment for tuberculosis (TB) in children, as per the **Revised National Tuberculosis Control Program (RNTCP/NTEP)** and WHO guidelines, consists of five primary drugs: **Isoniazid (H), Rifampicin (R), Pyrazinamide (Z), Ethambutol (E), and Streptomycin (S).** **Why Option D is correct:** Both **Streptomycin** and **Pyrazinamide** are classified as first-line anti-tubercular drugs (ATD). Pyrazinamide is essential during the intensive phase for its bactericidal activity against intracellular bacilli. Streptomycin, an aminoglycoside, is also a first-line agent, though its use is now primarily reserved for specific regimens (like the Category II retreatment regimen) or as a substitute when other first-line drugs are contraindicated. Since both belong to the first-line category, Option D is the most comprehensive choice. **Why other options are incorrect:** * **Options A & B:** While both are first-line drugs, selecting one over the other makes the answer incomplete. * **Option C (Ethionamide):** This is a **second-line** anti-tubercular drug used primarily in the management of Multi-Drug Resistant TB (MDR-TB) or when there is resistance/intolerance to first-line agents. **High-Yield Clinical Pearls for NEET-PG:** * **Ethambutol in Children:** Previously avoided due to the risk of optic neuritis (difficult to monitor in young children), it is now considered safe and included in pediatric dosages (15-25 mg/kg). * **Dosage Calculation:** Pediatric doses are generally higher per kg body weight than adult doses because children metabolize these drugs faster. * **Pyrazinamide Side Effect:** Most common is hepatotoxicity and hyperuricemia (though gout is rare in children). * **Streptomycin Side Effect:** Ototoxicity (8th cranial nerve damage) and nephrotoxicity. It is the only first-line drug given via the parenteral route.

Question 243: All are complications of diphtheria, except?

A. Myocarditis
B. Ocular muscle palsy
C. Cerebellar ataxia
D. Hepatic failure (Correct Answer)

Explanation: **Explanation:** Diphtheria is caused by *Corynebacterium diphtheriae*, which produces a potent **exotoxin** that inhibits protein synthesis (via ADP-ribosylation of Elongation Factor-2). While the bacteria remain localized to the upper respiratory tract (forming a pseudomembrane), the toxin spreads hematogenously, primarily affecting the heart, nervous system, and kidneys. **Why Hepatic Failure is the correct answer:** Hepatic failure is **not** a recognized complication of diphtheria. The toxin specifically targets tissues with high concentrations of receptors for the toxin, such as cardiac and neural tissues. While systemic toxemia can cause general malaise, the liver is not a primary target organ for the diphtheria toxin. **Analysis of other options:** * **Myocarditis (Option A):** This is the most common and most serious complication, occurring in about 10–25% of patients. It typically appears in the second week and is a leading cause of death. * **Ocular muscle palsy (Option B):** Neurological complications are common. **Cranial nerve palsies** (especially involving the soft palate, ciliary muscles causing blurring of vision, and extraocular muscles) typically occur in the 3rd to 5th week. * **Cerebellar ataxia (Option C):** While less common than peripheral neuropathy or palatal palsy, post-diphtheritic neurological involvement can rarely manifest as ataxia or encephalopathy due to the neurotoxic effects of the exotoxin. **NEET-PG High-Yield Pearls:** * **Most common cause of death:** Myocarditis. * **First sign of neurological involvement:** Palatal palsy (nasal twang/regurgitation). * **Treatment Priority:** Administer **Diphtheria Antitoxin (DAT)** immediately based on clinical suspicion; do not wait for culture results. * **Antibiotic of choice:** Erythromycin or Penicillin G (used to stop toxin production and prevent spread, but does not neutralize circulating toxin).

Question 244: What drug is used in the treatment of Respiratory Syncytial Virus (RSV) infection in children?

A. Rituximab
B. Palivizumab (Correct Answer)
C. None of the above
D. Omalizumab

Explanation: **Explanation:** **Respiratory Syncytial Virus (RSV)** is the most common cause of bronchiolitis and pneumonia in infants and young children. **Why Palivizumab is correct:** Palivizumab is a **humanized monoclonal antibody** directed against the **F (fusion) protein** of RSV. By binding to this protein, it prevents the virus from entering the host cells and inhibits cell-to-cell fusion (syncytia formation). It is primarily used as **immunoprophylaxis** to prevent severe lower respiratory tract disease in high-risk infants (e.g., preterm infants, those with bronchopulmonary dysplasia, or hemodynamically significant congenital heart disease). **Why the other options are incorrect:** * **Rituximab (A):** A chimeric monoclonal antibody against **CD20** found on B-cells. It is used in lymphomas, leukemias, and autoimmune disorders, not viral infections. * **Omalizumab (D):** A recombinant DNA-derived humanized IgG1k monoclonal antibody that selectively binds to **human immunoglobulin E (IgE)**. It is used in the management of moderate-to-severe persistent allergic asthma. **High-Yield Clinical Pearls for NEET-PG:** * **Ribavirin:** While Palivizumab is for prophylaxis, **nebulized Ribavirin** is the only antiviral agent specifically approved for the *treatment* of severe RSV, though its use is clinically limited due to toxicity and cost. * **Administration:** Palivizumab is administered **intramuscularly** once a month during the RSV season (usually 5 doses). * **Diagnosis:** The gold standard for RSV diagnosis is **RT-PCR**, though Rapid Antigen Detection Tests (RADT) are commonly used in clinical practice. * **Radiology:** Chest X-ray in RSV bronchiolitis typically shows **hyperinflation** and patchy atelectasis.

Question 245: A 5-year-old girl presents with a several-day history of localized swelling in the right side of her neck. There is no recent history of sore throat. Physical examination reveals a low-grade fever and one very tender, firm, slightly enlarged lymph node in the right cervical region. A CBC shows mild leukocytosis, and fine needle aspiration of the lymph node reveals scattered neutrophils. Which of the following is the most likely diagnosis?

A. Bacterial lymphadenitis (Correct Answer)
B. Granulomatous lymphadenitis
C. Necrotizing lymphadenitis
D. Toxoplasmic lymphadenitis

Explanation: **Explanation:** The clinical presentation of acute, localized, tender, and firm cervical lymphadenitis associated with fever and leukocytosis in a child is most characteristic of **Bacterial Lymphadenitis**. 1. **Why the correct answer is right:** Acute unilateral cervical lymphadenitis in children is most commonly caused by *Staphylococcus aureus* or *Streptococcus pyogenes*. The presence of **exquisite tenderness**, localized swelling, fever, and a CBC showing **leukocytosis** points toward an acute pyogenic infection. The fine needle aspiration (FNA) finding of **scattered neutrophils** further confirms an acute inflammatory process typical of bacterial etiology. 2. **Why the incorrect options are wrong:** * **Granulomatous lymphadenitis:** Usually caused by *Mycobacterium tuberculosis* or atypical mycobacteria. It typically presents as chronic, non-tender "cold" swelling. Histology would show granulomas and giant cells, not just neutrophils. * **Necrotizing lymphadenitis (Kikuchi-Fujimoto disease):** This is a rare, benign cause of fever and lymphadenopathy. However, histology typically shows paracortical necrosis with karyorrhectic debris and a lack of neutrophils. * **Toxoplasmic lymphadenitis:** Usually presents as asymptomatic or mildly tender posterior cervical lymphadenopathy. Histology shows reactive follicular hyperplasia and clusters of epithelioid histiocytes. **Clinical Pearls for NEET-PG:** * **Most common cause of acute unilateral lymphadenitis:** *S. aureus* (followed by Group A Streptococcus). * **Most common cause of subacute/chronic bilateral lymphadenitis:** Viral infections (EBV, CMV). * **Cat-scratch disease (*Bartonella henselae*):** A common cause of subacute regional lymphadenitis; look for a history of a kitten scratch and stellate necrosis on biopsy. * **Management:** Empiric antibiotics (e.g., Cephalexin or Clindamycin) are the first line for suspected bacterial lymphadenitis. If fluctuant, incision and drainage may be required.

Question 246: What virus can cause Roseola infantum?

A. Herpes virus 6
B. Parvovirus B 19
C. Echovirus 19
D. All of the above (Correct Answer)

Explanation: **Explanation:** **Roseola Infantum**, also known as **Exanthem Subitum** or **Sixth Disease**, is a common childhood illness characterized by a high-grade fever (often >39.5°C) for 3–5 days, followed by a sudden cessation of fever and the appearance of a maculopapular rash. **Why "All of the above" is correct:** While **Human Herpesvirus 6 (HHV-6)** is the most common and classic causative agent (responsible for up to 90% of cases), it is not the only one. **HHV-7** is the second most common cause. However, medical literature and clinical studies have also identified other viruses that can produce an identical clinical syndrome of high fever followed by a rash. These include **Echovirus 16** (historically known as Boston Exanthem), **Echovirus 19**, **Parvovirus B19**, and occasionally Adenovirus or Coxsackieviruses. Therefore, in the context of a multiple-choice question where these specific viruses are listed, "All of the above" is the most accurate clinical answer. **Clinical Pearls for NEET-PG:** * **The "Fever-Rash" Sequence:** This is the most high-yield diagnostic feature. The rash appears **only after** the fever subsides (defervescence). * **Nagayama Spots:** Small erythematous papules on the soft palate and uvula (seen in 2/3 of patients). * **Complications:** Due to the rapid rise in temperature, **Febrile Seizures** are the most common complication of Roseola. * **Age Group:** Typically affects children aged 6 months to 2 years (maternal antibodies protect those <6 months). * **Treatment:** Supportive care; the condition is self-limiting. Cidofovir or Ganciclovir is reserved only for severe cases in immunocompromised patients.

Question 247: Which of the following is NOT a feature of congenital rubella syndrome?

A. Cardiac abnormality
B. Renal anomalies (Correct Answer)
C. Deafness
D. Cataract

Explanation: **Explanation:** Congenital Rubella Syndrome (CRS) occurs due to transplacental transmission of the Rubella virus, primarily during the first trimester. The classic clinical presentation is defined by **Gregg’s Triad**, which includes: 1. **Cataracts** (and other ocular defects like microphthalmia or glaucoma). 2. **Sensorineural Deafness** (the most common finding). 3. **Cardiac Abnormalities** (most commonly Patent Ductus Arteriosus (PDA) and Peripheral Pulmonary Artery Stenosis). **Why Option B is correct:** **Renal anomalies** are not a characteristic feature of CRS. While the virus can affect multiple organs (causing hepatosplenomegaly or radiolucent bone lesions), the renal system is typically spared. Renal anomalies are more frequently associated with other conditions, such as Turner syndrome or VACTERL association. **Why other options are incorrect:** * **Option A (Cardiac abnormality):** PDA is the hallmark cardiac lesion in CRS. * **Option C (Deafness):** Sensorineural hearing loss is the most frequent manifestation of CRS and may be the only finding in late-gestation infections. * **Option D (Cataract):** Ocular defects, particularly "pearlescent" nuclear cataracts, are a core component of the syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **"Blueberry Muffin" Rash:** Represents extramedullary hematopoiesis (also seen in CMV). * **Salt and Pepper Retinopathy:** The most common ocular finding in CRS (though cataracts are more classic for exams). * **Expanded CRS:** Includes microcephaly, mental retardation, and "celery stalking" appearance of long bones on X-ray. * **Risk Timing:** The risk of malformation is highest (up to 80%) if the mother is infected within the first 12 weeks of pregnancy.

Question 248: Which of the following statements is/are true about meningitis?

A. Epidemics are caused by H. influenzae. (Correct Answer)
B. E. coli and Group B Streptococci are the most common causes in the neonatal period.
C. The Hib vaccine is effective in the prevention of meningitis.
D. Epidemics caused by meningococcus group B are common.

Explanation: **Explanation:** The correct statement is **A**, as *Haemophilus influenzae* type b (Hib) was historically the leading cause of both endemic and epidemic bacterial meningitis in children before the widespread implementation of the Hib conjugate vaccine. While *Neisseria meningitidis* is the most notorious cause of large-scale epidemics (especially in the "meningitis belt"), *H. influenzae* has been documented to cause significant localized outbreaks and high-burden clusters in unvaccinated populations. **Analysis of Options:** * **Option B:** This statement is **true** but was not marked as the primary answer in the provided key. In the neonatal period (0-28 days), *Group B Streptococcus* (GBS) and *E. coli* are indeed the most common pathogens. * **Option C:** This statement is **true**. The Hib conjugate vaccine is highly effective and has reduced the incidence of Hib meningitis by over 90% in countries where it is part of the routine immunization schedule. * **Option D:** This is **incorrect**. While *Neisseria meningitidis* causes epidemics, they are most commonly caused by serogroups **A, C, W-135, and Y**. Serogroup B is more commonly associated with sporadic cases because its polysaccharide capsule is poorly immunogenic. **NEET-PG High-Yield Pearls:** * **Most common cause overall (Post-neonatal):** *Streptococcus pneumoniae*. * **Waterhouse-Friderichsen Syndrome:** Adrenal hemorrhage associated with meningococcemia. * **CSF Findings in Bacterial Meningitis:** Low glucose (<40 mg/dL), high protein (>100 mg/dL), and polymorphonuclear pleocytosis. * **Drug of Choice:** Third-generation cephalosporins (Ceftriaxone/Cefotaxime). In neonates, Ampicillin is added to cover *Listeria monocytogenes*.

Question 249: What is the recommended single dose of Albendazole for a 10-year-old child being treated for roundworm infestation?

A. 200 mg
B. 400 mg (Correct Answer)
C. 1 g
D. 2 g

Explanation: **Explanation:** The correct answer is **400 mg (Option B)**. Albendazole is a broad-spectrum anthelmintic agent that works by inhibiting tubulin polymerization, leading to the metabolic disruption and death of the helminth. According to the World Health Organization (WHO) and the National Deworming Day (NDD) guidelines in India, the dosing for Albendazole in soil-transmitted helminth (STH) infections like *Ascaris lumbricoides* (roundworm) is age-dependent: * **Children aged 12–24 months:** 200 mg (half tablet) as a single dose. * **Children aged >24 months (2 years) to adults:** 400 mg (single tablet) as a single dose. Since the child in the question is 10 years old, the standard adult dose of 400 mg is indicated. **Analysis of Incorrect Options:** * **Option A (200 mg):** This is the recommended dose for children between 12 and 24 months of age. * **Options C and D (1 g and 2 g):** These doses are excessively high for a single treatment of roundworm and carry a significant risk of toxicity without added therapeutic benefit. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Binds to β-tubulin, inhibiting microtubule synthesis. * **Drug of Choice (DOC):** Albendazole is the DOC for Ascariasis, Hookworm, Enterobiasis (Pinworm), and Neurocysticercosis. * **Neurocysticercosis Dosing:** Unlike the single dose for worms, treatment for neurocysticercosis requires 15 mg/kg/day (max 800 mg) for 8–30 days, often co-administered with steroids to prevent inflammatory reactions. * **Contraindication:** Albendazole is generally avoided in the first trimester of pregnancy (teratogenic potential).

Question 250: A 1 and 1/2 year old child with a history of chronic diarrhea presents with perioral and perineal rash. What is your diagnosis?

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

Explanation: ### Explanation **Correct Answer: C. Acrodermatitis enteropathica** **Mechanism and Clinical Presentation:** Acrodermatitis enteropathica (AE) is an autosomal recessive disorder caused by a mutation in the **SLC39A4 gene**, which encodes a zinc transporter protein. This leads to severe **zinc deficiency**. The classic clinical triad includes: 1. **Dermatitis:** Vesiculobullous or eczematous lesions specifically in **perioral, acral (extremities), and perineal/diaper areas**. 2. **Alopecia.** 3. **Diarrhea.** Symptoms typically manifest in infancy, often shortly after weaning from breast milk to cow's milk (as breast milk contains a zinc-binding ligand that aids absorption). **Why Incorrect Options are Wrong:** * **A. Epidermolysis bullosa:** A genetic mechanobullous disorder characterized by skin fragility and blistering in response to minor trauma. It does not typically present with chronic diarrhea. * **B. Staphylococcal scalded skin syndrome (SSSS):** Caused by *Staph. aureus* exfoliative toxins. It presents with diffuse erythema and skin peeling (Nikolsky sign positive), usually following a prodrome of fever and irritability, not chronic diarrhea. * **D. Toxic epidermal necrolysis (TEN):** A severe drug reaction involving >30% body surface area skin detachment and mucosal involvement. It is an acute, life-threatening emergency, not a chronic condition associated with nutritional malabsorption. **High-Yield Pearls for NEET-PG:** * **Inheritance:** Autosomal Recessive (SLC39A4 mutation). * **Diagnosis:** Low serum zinc levels (though clinical response to zinc is definitive). * **Treatment:** Lifelong oral **Zinc supplementation** (elemental zinc 1-3 mg/kg/day). * **Acquired Form:** Can occur in patients on prolonged Total Parenteral Nutrition (TPN) without zinc supplementation or in severe malabsorption syndromes.

Practice by Chapter

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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