A 6-month-old male presents for a routine visit to his pediatrician. Two months ago, the patient was seen for tachypnea and wheezing, and diagnosed with severe respiratory syncytial virus (RSV) bronchiolitis. After admission to the hospital and supportive care, the patient recovered and currently is not experiencing any trouble breathing. Regarding the possibility of future reactive airway disease, which of the following statements is most accurate?

“Your child has a greater than 20% chance of developing asthma”

“There is no clear relationship between RSV and the development of asthma.”

“Your child’s risk of asthma is less than the general population.”

“Your child has a less than 5% chance of developing asthma”

“Your child’s risk of asthma is the same as the general population.”

A patient is hospitalized for pneumonia. Gram-positive cocci in clusters are seen on sputum gram stain. Which of the following clinical scenarios is most commonly associated with this form of pneumonia?

Hospitalized adult with development of pneumonia symptoms 2 weeks following a viral illness

Elderly patient who has trouble swallowing and poor dentition

An alcoholic with evidence of empyema and "currant jelly sputum"

An otherwise healthy young adult with a week of mild fatigue, chills, and cough

HIV positive adult with a CD4 count less than 150 and an impaired diffusion capacity

A 9-year-old girl presents with a 3-week history of cough. Her mother reports that initially, she had a runny nose and was tired, with a slight cough, but as the runny nose resolved, the cough seemed to get worse. She further states that the cough is dry sounding and occurs during the day and night. She describes having coughing spasms that occasionally end in vomiting, but between episodes of coughing she is fine. She reports that during a coughing spasm, her daughter will gasp for air and sometimes make a “whooping” noise. A nasopharyngeal swab confirms a diagnosis of Bordetella pertussis. Which of the following statements apply to this patient?

Her 3-month-old brother should be treated with azithromycin as prophylaxis.

She should be started on azithromycin for more rapid resolution of cough.

Her classmates should be treated with clarithromycin as prophylaxis.

She will have lifelong natural immunity against Bordetella pertussis.

Her classmates should receive a Tdap booster regardless of their vaccination status.

An 8-year-old boy presents to his pediatrician accompanied by his father with a complaint of chronic cough. For the past 2 months he has been coughing up yellow, foul-smelling sputum. He has been treated at a local urgent care center for multiple episodes of otitis media, sinusitis, and bronchitis since 2 years of age. His family history is unremarkable. At the pediatrician's office, his temperature is 99.2°F (37.3°C), blood pressure is 110/84 mmHg, pulse is 95/min, and respirations are 20/min. Inspection shows a young boy who coughs occasionally during examination. Pulmonary exam demonstrates diffuse wheezing and crackles bilaterally. Mild clubbing is present on the fingers. The father has brought an electrocardiogram (ECG) from the patient’s last urgent care visit that shows pronounced right axis deviation. Which of the following is the most likely etiology of this patient’s condition?

Failure of neural crest cell migration

Maldevelopment of pharyngeal pouches

Defective maturation of B-lymphocytes

A 10-year-old girl is admitted to the medical floor for a respiratory infection. The patient lives in a foster home and has been admitted many times. Since birth, the patient has had repeated episodes of pain/pressure over her frontal sinuses and a chronic cough that produces mucus. She was recently treated with amoxicillin for an infection. The patient is in the 25th percentile for height and weight which has been constant since birth. Her guardians state that the patient has normal bowel movements and has been gaining weight appropriately. The patient has a history of tricuspid stenosis. She also recently had magnetic resonance imaging (MRI) of her chest which demonstrated dilation of her airways. Her temperature is 99.5°F (37.5°C), blood pressure is 90/58 mmHg, pulse is 120/min, respirations are 18/min, and oxygen saturation is 94% on room air. Physical exam is notable for bruises along the patient's shins which the guardians state are from playing soccer. The rest of the exam is deferred because the patient starts crying. Which of the following findings is associated with this patient's most likely underlying diagnosis?

Increased chloride in the patient's sweat

Social withdrawal and avoidance of eye contact

Repeat sinus infections secondary to seasonal allergies

Diastolic murmur best heard along the right lower sternal border

Pediatric respiratory infections for USMLE Step 3: High-Yield Pediatrics Lessons

Croup & Epiglottitis - Airway Alarms

Croup (Laryngotracheobronchitis): Viral (Parainfluenza), age 6 mo-3 yr. Gradual onset with barking cough, inspiratory stridor. X-ray: Steeple sign. Mgt: Steroids, nebulized epinephrine.
Epiglottitis: Bacterial (H. influenzae), age 2-7 yr. Rapid onset, toxic look, drooling, dysphagia, tripod position. X-ray: Thumb sign. Mgt: Intubation, antibiotics.

Thumb sign (Epiglottitis) vs. Steeple sign (Croup) X-rays

⭐ In suspected epiglottitis, do NOT attempt to examine the throat with a tongue depressor; it can precipitate complete airway obstruction.

Bronchiolitis - Wheezy Baby Blues

Etiology: Respiratory Syncytial Virus (RSV) is the most common cause (>50%). Primarily affects infants <2 years old, peaking at 3-6 months.
Clinical Triad: Presents with coryza, persistent cough, and respiratory distress (tachypnea, retractions, wheezing/crackles).
Diagnosis: Primarily clinical. Chest X-ray is not routinely recommended but may show hyperinflation, peribronchial thickening, and atelectasis.
💡 Management: Supportive care is key! Oxygen to maintain SpO₂ >92%, hydration, and nasal suctioning. Bronchodilators and corticosteroids are not routinely used.
Prevention: Palivizumab monoclonal antibody for high-risk infants (preterm, chronic lung disease).

⭐ RSV is the leading cause of lower respiratory tract infections in infants worldwide, making it a top differential for any wheezy baby.

Pediatric Pneumonia - Lungs Under Siege

Etiology by Age:
- Neonate: GBS, E. coli, Listeria.
- 1-3 mo: Chlamydia trachomatis (staccato cough), RSV.
- 3 mo - 5 yr: S. pneumoniae (most common), H. influenzae.
- >5 yr: Mycoplasma pneumoniae, S. pneumoniae.
Diagnosis: Based on WHO criteria for fast breathing (tachypnea):
- <2 months: >60/min
- 2-12 months: >50/min
- 1-5 years: >40/min

Chest X-ray: Lobar consolidation in pediatric pneumonia

⭐ Mycoplasma pneumoniae is the leading cause of atypical pneumonia in school-aged children, often called "walking pneumonia."

Pertussis - The 100-Day Cough

Agent: Bordetella pertussis (Gram-negative coccobacillus).
Phases:

Diagnosis: Nasopharyngeal swab for PCR (most sensitive) or culture (gold standard). Classic finding: Absolute lymphocytosis.
Treatment: Macrolides (Azithromycin). Treat close contacts.

⭐ The classic inspiratory “whoop” is often absent in infants < 6 months; they may present with apnea instead.

Chest X-ray: Perihilar infiltrates in pediatric pertussis

High‑Yield Points - ⚡ Biggest Takeaways

Croup (Laryngotracheobronchitis) is caused by Parainfluenza virus, presenting with a barking cough and steeple sign on X-ray.

Epiglottitis, a medical emergency, is classically due to H. influenzae and shows a thumb sign on lateral X-ray.

Bronchiolitis in infants is most commonly caused by RSV, leading to expiratory wheezing.

The most common cause of typical bacterial pneumonia is Streptococcus pneumoniae.

Pertussis features a paroxysmal cough with an inspiratory ‘whoop’.

Diphtheria presents with a greyish pseudomembrane and ‘bull neck’.

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