Chest X-ray Analysis: 45-day-old Female with Cough

X-ray Findings (AP View)

• Lungs: Bilateral hyperinflation is present - the lung fields appear more radiolucent (dark) than expected for this age, with increased AP diameter. The diaphragm appears relatively flattened.
• Perihilar/peribronchial region: There is increased interstitial markings/peribronchial cuffing bilaterally around the hila.
• Right side: There appears to be subtle increased opacity in the right perihilar region, possibly consistent with peribronchial thickening.
• No focal lobar consolidation is clearly identified.
• No pleural effusion visible.
• Heart size: Appears normal.
• Ribs: Horizontal rib orientation consistent with air trapping/hyperinflation.

Radiological Pattern

Top Differential Diagnoses

1. Bronchiolitis (Most Likely) - RSV or other viral

• Classic CXR: hyperinflation, peribronchial cuffing, patchy atelectasis
• Peak age: <2 years (common even at 6 weeks)
• Rosen's Emergency Medicine: "Hyperinflation, atelectasis, and peribronchial cuffing are the radiography findings most commonly associated with bronchiolitis"

2. Chlamydial Pneumonia - Should be high on the list at this age

• Chlamydia trachomatis classically presents at 4-12 weeks of age
• Radiograph: interstitial opacification with hyperinflation - exactly matches this film
• Afebrile staccato cough is characteristic
• Associated conjunctivitis history in mother/infant is a clue
• Grainger & Allison Radiology: "Chlamydial infection classically presents first with conjunctivitis at 1-2 weeks after birth and the lung infection does not usually become evident until 4-12 weeks of age. Typically the radiograph demonstrates interstitial opacification with some hyperinflation."

3. Neonatal/Young Infant Pneumonia (Bacterial)

• Group B Streptococcus, Ureaplasma, S. aureus
• More commonly shows focal consolidation or bilateral asymmetric alveolar opacification
• Less likely given the diffuse interstitial pattern here

4. Pertussis (Whooping Cough)

• Can cause the classic "shaggy heart sign" with perihilar infiltrates
• In a 45-day-old, may not yet have received vaccine
• Consider if paroxysmal cough, post-tussive vomiting, apnea

Key Clinical Considerations for a 45-day-old

Recommended Workup

1. NPA (Nasopharyngeal Aspirate) for RSV, Influenza, Parainfluenza, Rhinovirus rapid panel
2. Chlamydia trachomatis PCR (nasopharynx or blood) - critical given the age
3. Pertussis PCR - especially if cough is paroxysmal
4. CBC + CRP - neutrophilia suggests bacterial; eosinophilia suggests Chlamydia
5. Blood culture if systemically unwell
6. Oxygen saturation monitoring

Management Principles

• Oxygen supplementation if SpO2 <94%
• Nasal suctioning (bulb/suction catheter)
• Adequate hydration (IV or NG if feeding poorly)
• Monitor for apnea (high risk in this age group)

• If Chlamydia suspected: Azithromycin 10 mg/kg/day x 5 days (first-line; erythromycin is alternative but associated with pyloric stenosis risk in young infants)
• If pertussis suspected: Azithromycin x 5 days
• Avoid: Routine bronchodilators (SABAs) are not recommended for viral bronchiolitis in infants; nebulized 3% saline has limited evidence
• Antibiotics not indicated for pure viral bronchiolitis

Red Flags Requiring Immediate Action

• Apnea or bradycardia (common in infants <6 weeks with RSV/pertussis)
• SpO2 <90% on room air
• Poor feeding (<50% normal intake)
• Respiratory rate >60/min
• Grunting, severe retractions, nasal flaring
• Altered consciousness

Sources: Rosen's Emergency Medicine 9th Ed.; Grainger & Allison's Diagnostic Radiology; Australasian Bronchiolitis Guideline 2025 (PMID 40685806)