Infectious Diseases Practice Questions

Q: A 2-year-old boy presents with fever and rhinorrhea, followed by a maculopapular rash that spread from the face to the neck, chest, and arms in that order. What is the most likely diagnosis?

Measles. ### Explanation **Correct Option: A. Measles (Rubeola)** The clinical presentation described is classic for Measles. The diagnosis is based on the characteristic **cephalocaudal progression** of the rash. The maculopapular rash typically appears 3–4 days after the onset of prodromal symptoms (fever, cough, coryza, and conjunctivitis). It begins behind the ears and at the hairline, then spreads downward to the face, neck, trunk, and extremities (centrifugal spread). As the rash fades, it often leaves behind brownish discoloration or fine desquamation. **Why Incorrect Options are Wrong:** * **B. Meningococcal septicemia:** This typically presents with a rapidly progressing **petechial or purpuric rash** (non-blanching), often accompanied by signs of shock or meningitis. It does not follow a slow cephalocaudal maculopapular pattern. * **C. Hemophilia:** This is a bleeding disorder, not an infectious disease. It presents with deep tissue bleeds, hemarthrosis, or prolonged bruising, not a febrile maculopapular rash. * **D. Chickenpox (Varicella):** The rash in chickenpox is **pleomorphic** (papules, vesicles, and crusts present simultaneously) and follows a **centripetal distribution** (starts on the trunk and spreads to the face and limbs), which is the opposite of Measles. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik spots:** Pathognomonic bluish-white spots on the buccal mucosa opposite the lower molars; they appear *before* the rash. * **Vitamin A:** Supplementation is recommended for all children with measles to reduce morbidity and mortality. * **Complications:** The most common complication is **Otitis Media**; the most common cause of death is **Pneumonia**; the most dreaded late complication is **SSPE** (Subacute Sclerosing Panencephalitis). * **Isolation:** Respiratory isolation is required for 4 days after the appearance of the rash.

Q: What is the most common cause of Hepatitis B in a 3-year-old child?

Perinatal transmission. **Explanation:** The most common cause of Hepatitis B Virus (HBV) infection in children worldwide, particularly in endemic regions, is **Perinatal (Vertical) Transmission**. This occurs from an HBsAg-positive mother to her newborn during delivery. In a 3-year-old child, the infection is almost always a result of this early exposure, as the risk of developing chronic HBV is inversely proportional to the age at which the infection is acquired (90% risk in neonates vs. <5% in adults). **Analysis of Options:** * **Perinatal Transmission (Correct):** This is the primary driver of the pediatric HBV burden. Transmission usually occurs during birth via contact with maternal blood and vaginal secretions. * **Pin prick (Incorrect):** While a risk for healthcare workers or through accidental needle sticks, it is a rare occurrence in the general pediatric population compared to vertical transmission. * **Saliva exchange (Incorrect):** Although HBV DNA can be detected in saliva, it is not considered an efficient or common route of transmission, especially in early childhood. * **Blood transfusion (Incorrect):** Due to mandatory and stringent screening of blood donors for HBsAg, transfusion-associated Hepatitis B is now extremely rare. **Clinical Pearls for NEET-PG:** * **Chronicity Risk:** The younger the age of infection, the higher the risk of chronicity. * **Immunoprophylaxis:** To prevent vertical transmission, infants born to HBsAg+ mothers should receive both the **HBV Vaccine** and **Hepatitis B Immunoglobulin (HBIG)** within 12 hours of birth. * **HBeAg Status:** If the mother is HBeAg positive, the risk of transmission to the baby is as high as 70-90%. * **Horizontal Transmission:** In older children, household contact (sharing toothbrushes or razors) is the second most common route in endemic areas.

Q: An unimmunized child presents with signs suggestive of diphtheria. Which type of diphtheria would suggest the worst prognosis?

Laryngeal. **Explanation:** The prognosis of diphtheria is primarily determined by the site of infection and the degree of toxin absorption. **Why Laryngeal Diphtheria is the worst prognosis:** Laryngeal involvement is considered the most dangerous form because it carries a high risk of **acute airway obstruction**. The characteristic "pseudomembrane" can detach or cause significant edema, leading to stridor, respiratory distress, and death by asphyxiation. Furthermore, laryngeal diphtheria is often a downward extension of pharyngeal infection, indicating a high toxin load and a greater risk of systemic complications like myocarditis and neuritis. **Analysis of Incorrect Options:** * **Tonsillopharyngeal:** This is the most common form. While it can lead to significant toxin absorption (causing "bull neck" lymphadenopathy), the immediate risk of sudden airway occlusion is lower than in the laryngeal form. * **Nasal:** This is generally the mildest form. It presents with serosanguinous discharge. Because the nasal mucosa is less vascularized for toxin absorption, systemic complications are rare. * **Cutaneous:** This presents as non-healing ulcers. It often acts as a reservoir for the bacteria but rarely leads to systemic toxicity or mortality. **Clinical Pearls for NEET-PG:** * **Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **Pathogenesis:** Mediated by an exotoxin that inhibits protein synthesis via **ADP-ribosylation of Elongation Factor-2 (EF-2)**. * **Diagnosis:** Culture on **Löffler's serum slope** or **Potassium Tellurite agar** (black colonies). * **Treatment:** Immediate administration of **Diphtheria Antitoxin (DAT)** is the priority, as it only neutralizes unbound toxin. Antibiotics (Penicillin or Erythromycin) are used to stop further toxin production and spread.

Q: Which of the following organisms causes pneumatocele in children in association with pneumonia?

Staphylococcus aureus. **Explanation:** **Staphylococcus aureus** is the most common cause of **pneumatoceles** (thin-walled, air-filled cysts within the lung parenchyma) in children. The underlying mechanism involves the production of toxins and enzymes (such as Panton-Valentine Leukocidin) that cause focal necrosis of the bronchial wall. This creates a "check-valve" mechanism where air enters the interstitial space during inspiration but becomes trapped during expiration, leading to the formation of these characteristic air-filled cavities. **Analysis of Options:** * **Streptococcus pneumoniae:** While it is the most common cause of community-acquired pneumonia in children, it typically presents with lobar consolidation. It rarely causes cavitation or pneumatoceles. * **Klebsiella pneumoniae:** This organism is known for causing "Friedlander’s pneumonia" with a "bulging fissure sign." While it can cause lung abscesses and necrosis (especially in neonates or immunocompromised adults), it is not the classic association for pneumatoceles in the pediatric population. * **Haemophilus influenzae:** Typically causes bronchopneumonia or pleural effusions/empyema, but it does not have the necrotizing tendency required to form pneumatoceles. **High-Yield Clinical Pearls for NEET-PG:** * **Staphylococcal Pneumonia:** Often follows a viral prodrome (like Influenza). It is characterized by rapid progression, empyema, pyopneumothorax, and pneumatoceles. * **Management:** Most pneumatoceles are asymptomatic and resolve spontaneously over weeks to months; surgical intervention is rarely required unless they cause tension pneumothorax or become infected. * **Radiology:** Look for the "Air-fluid level" within a thin-walled cyst on a chest X-ray in a child with severe respiratory distress.

Q: A baby is born to a mother with AIDS. Which of the following statements is true regarding the infant, except?

50% chance of acquiring AIDS. In vertical transmission of HIV, the risk of a baby acquiring the infection from an untreated mother is approximately **25–30%** (not 50%). With modern interventions, including Highly Active Antiretroviral Therapy (HAART) for the mother, elective cesarean section, and avoidance of breastfeeding, this risk can be reduced to **less than 1–2%**. Therefore, Option C is the incorrect statement (the "except" answer). **Explanation of Options:** * **Option A (Failure to Thrive):** This is a hallmark clinical feature of pediatric HIV. Affected infants often show poor weight gain and growth retardation due to chronic infections, malabsorption, and the hypermetabolic state of the disease. * **Option B (Infections):** HIV-infected infants are highly susceptible to opportunistic infections. Common presentations include recurrent bacterial infections, persistent oral candidiasis (thrush), and *Pneumocystis jirovecii* pneumonia (the most common opportunistic infection in the first year of life). * **Option D:** Since Option C is statistically inaccurate, "All of the above" cannot be the correct choice. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** In infants <18 months, **DNA-PCR** (detecting the virus) is the gold standard because maternal IgG antibodies cross the placenta and can persist for up to 18 months, making ELISA unreliable (false positives). 2. **Prophylaxis:** All HIV-exposed infants should receive **Cotrimoxazole prophylaxis** starting at 4–6 weeks of age to prevent *Pneumocystis* pneumonia until infection is ruled out. 3. **Feeding:** In India (NACO guidelines), exclusive breastfeeding is recommended for the first 6 months if replacement feeding is not "Acceptable, Feasible, Affordable, Sustainable, and Safe" (AFASS). Mixed feeding should be strictly avoided.

Q: All of the following statements about Recurrent Laryngeal Papillomatosis are true, EXCEPT:

HPV6 is more virulent than HPV11. **Explanation:** Recurrent Respiratory Papillomatosis (RRP) is the most common benign neoplasm of the larynx in children. The correct answer is **C** because it is a false statement; in clinical practice, **HPV-11 is considered more virulent** than HPV-6. HPV-11 is associated with a more aggressive clinical course, higher rates of airway obstruction, and a greater need for frequent surgical interventions. **Analysis of Options:** * **Option A & B:** RRP is caused by the **Human Papilloma Virus (HPV)**. Specifically, **types 6 and 11** are responsible for over 90% of cases. These are "low-risk" types (non-oncogenic), though rare malignant transformation to squamous cell carcinoma can occur. * **Option D:** The primary mode of transmission in the juvenile form is **vertical transmission** during birth. The neonate acquires the virus while passing through an infected birth canal (maternal genital warts/condyloma acuminatum). **Clinical Pearls for NEET-PG:** * **Triad of symptoms:** Hoarseness of voice (most common early sign), stridor (initially inspiratory), and chronic cough. * **Diagnosis:** Direct laryngoscopy shows characteristic "cauliflower-like" exophytic lesions. * **Management:** The gold standard is **Surgical Debridement** (CO2 laser or microdebrider) to maintain airway patency. It is not curative, as the virus remains latent in the basal layer of the mucosa. * **Adjuvant Therapy:** Cidofovir (antiviral) is sometimes used for aggressive cases. * **Prevention:** The quadrivalent and nonavalent HPV vaccines are highly effective in reducing the incidence of maternal transmission.

Question 1

A 2-year-old boy presents with fever and rhinorrhea, followed by a maculopapular rash that spread from the face to the neck, chest, and arms in that order. What is the most likely diagnosis?

Accepted Answer

Measles

Answer

Meningococcal septicemia

Answer

Hemophilia

Answer

Chickenpox

Question 2

What is the most common complication of chickenpox?

Accepted Answer

Secondary bacterial pneumonia

Answer

Varicella pneumonia

Answer

Chorioretinitis

Answer

Reye's syndrome

Question 3

What is the most common cause of Hepatitis B in a 3-year-old child?

Accepted Answer

Perinatal transmission

Answer

Pin prick

Answer

Saliva exchange

Answer

Blood transfusion

Question 4

What is the most common causative agent of meningitis in the age group of 6 months to 3 years?

Accepted Answer

Streptococcus agalactiae

Answer

Haemophilus influenzae

Answer

Staphylococcus

Answer

Neisseria gonorrhoeae

Question 5

An unimmunized child presents with signs suggestive of diphtheria. Which type of diphtheria would suggest the worst prognosis?

Accepted Answer

Laryngeal

Answer

Tonsillopharyngeal

Answer

Nasal

Answer

Cutaneous

Question 6

Which of the following organisms causes pneumatocele in children in association with pneumonia?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Klebsiella

Answer

Haemophilus influenzae

Question 7

A baby is born to a mother with AIDS. Which of the following statements is true regarding the infant, except?

Accepted Answer

50% chance of acquiring AIDS

Answer

Failure to thrive

Answer

Infections

Answer

All of the above are true

Question 8

All of the following statements about Recurrent Laryngeal Papillomatosis are true, EXCEPT:

Accepted Answer

HPV6 is more virulent than HPV11

Answer

Caused by Human Papilloma Virus (HPV)

Answer

HPV6 and HPV11 are most commonly implicated

Answer

Transmission to neonate occurs through contact with mother during vaginal delivery

Question 9

A 12-year-old boy with sickle cell disease presents with pain and swelling of the right lower extremity. A bone scan reveals osteomyelitis of the tibial diaphysis. Which organism is found more commonly in these cases than in the general population?

Accepted Answer

Salmonella species

Answer

Haemophilus influenzae

Answer

Klebsiella species

Answer

Bacteroides species

Question 10

A 4-month-old infant presents with failure to thrive, progressive muscular weakness, and poor head control. The mother states that she feeds the baby soy-based formula sweetened with honey. Which organism is most likely responsible for these symptoms?

Accepted Answer

Clostridium botulinum

Answer

Clostridium difficile

Answer

Clostridium perfringens

Answer

Clostridium tetani

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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