Pediatrics – Infectious Disease Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A
1.
A 6-month-old infant presents with fever, irritability, and a bulging
fontanelle. Lumbar puncture shows cloudy CSF with elevated WBCs,
high protein, and low glucose. Most likely diagnosis?
Answer: Bacterial meningitis
Rationale: Cloudy CSF with high WBC (neutrophils), low glucose, and
high protein is typical of bacterial meningitis in infants.
2.
A 2-year-old presents with sudden onset of fever, drooling, muffled
voice, and tripod positioning. What is the most likely pathogen?
Answer: Haemophilus influenzae type b (Hib)
Rationale: Classic presentation of epiglottitis, historically caused by
Hib, especially in unvaccinated children.
3.
Which vaccine has dramatically reduced the incidence of Hib
infections in children?
Answer: Hib conjugate vaccine
Rationale: Widespread vaccination has decreased epiglottitis,
meningitis, and septicemia caused by Hib.
4.
,A 4-year-old child presents with fever, sore throat, and a sandpaper-
like rash. What is the likely diagnosis?
Answer: Scarlet fever
Rationale: Caused by Group A Streptococcus (GAS) with exotoxin-
mediated rash.
5.
Which antibiotic is first-line treatment for scarlet fever in children?
Answer: Penicillin V
Rationale: GAS remains universally sensitive to penicillin, which is
safe and effective in children.
6.
A 3-year-old presents with cough, coryza, conjunctivitis, and Koplik
spots. Which disease is this?
Answer: Measles (Rubeola)
Rationale: The triad of cough, coryza, conjunctivitis, and Koplik spots
is pathognomonic.
7.
Which complication is most commonly associated with measles in
children?
Answer: Otitis media
Rationale: Measles predisposes to bacterial superinfections; otitis
media is the most frequent.
8.
, A 1-year-old presents with paroxysmal coughing followed by
inspiratory “whoop.” Most likely pathogen?
Answer: Bordetella pertussis
Rationale: Classic pertussis presentation: catarrhal phase,
paroxysmal coughing, and inspiratory whoop.
9.
What is the preferred antibiotic for treating pertussis in infants?
Answer: Azithromycin
Rationale: Macrolides are the treatment of choice; azithromycin is
safe for infants under 1 month.
10.
A neonate develops fever, poor feeding, and lethargy on day 5 of life.
Blood culture grows Gram-positive cocci in chains. Likely organism?
Answer: Group B Streptococcus (GBS)
Rationale: Early-onset neonatal sepsis is commonly caused by GBS
transmitted during delivery.
11.
What is the first-line prophylaxis for infants at risk of GBS infection?
Answer: Intrapartum penicillin G
Rationale: Administered to colonized mothers during labor to prevent
neonatal GBS sepsis.
12.
A 2-year-old presents with fever, vesicular rash starting on the face
and spreading to the trunk, and mild cough. Likely diagnosis?
Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A
1.
A 6-month-old infant presents with fever, irritability, and a bulging
fontanelle. Lumbar puncture shows cloudy CSF with elevated WBCs,
high protein, and low glucose. Most likely diagnosis?
Answer: Bacterial meningitis
Rationale: Cloudy CSF with high WBC (neutrophils), low glucose, and
high protein is typical of bacterial meningitis in infants.
2.
A 2-year-old presents with sudden onset of fever, drooling, muffled
voice, and tripod positioning. What is the most likely pathogen?
Answer: Haemophilus influenzae type b (Hib)
Rationale: Classic presentation of epiglottitis, historically caused by
Hib, especially in unvaccinated children.
3.
Which vaccine has dramatically reduced the incidence of Hib
infections in children?
Answer: Hib conjugate vaccine
Rationale: Widespread vaccination has decreased epiglottitis,
meningitis, and septicemia caused by Hib.
4.
,A 4-year-old child presents with fever, sore throat, and a sandpaper-
like rash. What is the likely diagnosis?
Answer: Scarlet fever
Rationale: Caused by Group A Streptococcus (GAS) with exotoxin-
mediated rash.
5.
Which antibiotic is first-line treatment for scarlet fever in children?
Answer: Penicillin V
Rationale: GAS remains universally sensitive to penicillin, which is
safe and effective in children.
6.
A 3-year-old presents with cough, coryza, conjunctivitis, and Koplik
spots. Which disease is this?
Answer: Measles (Rubeola)
Rationale: The triad of cough, coryza, conjunctivitis, and Koplik spots
is pathognomonic.
7.
Which complication is most commonly associated with measles in
children?
Answer: Otitis media
Rationale: Measles predisposes to bacterial superinfections; otitis
media is the most frequent.
8.
, A 1-year-old presents with paroxysmal coughing followed by
inspiratory “whoop.” Most likely pathogen?
Answer: Bordetella pertussis
Rationale: Classic pertussis presentation: catarrhal phase,
paroxysmal coughing, and inspiratory whoop.
9.
What is the preferred antibiotic for treating pertussis in infants?
Answer: Azithromycin
Rationale: Macrolides are the treatment of choice; azithromycin is
safe for infants under 1 month.
10.
A neonate develops fever, poor feeding, and lethargy on day 5 of life.
Blood culture grows Gram-positive cocci in chains. Likely organism?
Answer: Group B Streptococcus (GBS)
Rationale: Early-onset neonatal sepsis is commonly caused by GBS
transmitted during delivery.
11.
What is the first-line prophylaxis for infants at risk of GBS infection?
Answer: Intrapartum penicillin G
Rationale: Administered to colonized mothers during labor to prevent
neonatal GBS sepsis.
12.
A 2-year-old presents with fever, vesicular rash starting on the face
and spreading to the trunk, and mild cough. Likely diagnosis?
