What is the management for a 5-month-old patient with cystic fibrosis (CF) presenting with good air entry, bilateral stridor, and a positive Methicillin-Sensitive Staphylococcus Aureus (MSSA) culture?

Management of 5-Month-Old with Cystic Fibrosis, Bilateral Stridor, and MSSA

Treat the MSSA infection with an oral anti-staphylococcal antibiotic (such as cephalexin or dicloxacillin) and urgently evaluate the stridor for potential airway obstruction, as stridor in an infant with CF is not typical and may indicate a separate acute process requiring immediate intervention.

Immediate Assessment and Airway Management

The bilateral stridor is the most concerning finding and requires urgent evaluation, as this is not a typical manifestation of CF lung disease in infants and suggests potential upper airway obstruction or a concurrent condition 1, 2. The "good air entry" suggests the lower airways are patent, but stridor indicates turbulent flow in the upper airways that needs immediate assessment.

MSSA Treatment Strategy

Antibiotic Selection for MSSA

• Oral anti-staphylococcal antibiotics are appropriate for MSSA in CF patients at this age 3, 2
• First-line options include cephalexin or dicloxacillin, as these provide targeted coverage against methicillin-sensitive Staphylococcus aureus 1, 4
• Treatment duration should be 14 days for respiratory tract infections in CF patients 3, 2

Important Considerations for MSSA Management

• The CF Foundation recommends against prophylactic anti-staphylococcal antibiotics in CF patients, as this approach does not improve lung function, quality of life, or reduce exacerbations 3
• However, when MSSA is documented on culture with clinical signs of infection, treatment is indicated 2
• At 5 months of age, this infant is too young for the standard CF maintenance therapies (which typically begin at age 6 years), so focus on treating the acute infection 3

Critical Pitfalls to Avoid

Do Not Confuse MSSA with Pseudomonas Management

• MSSA does not require antipseudomonal antibiotics 3, 5, 6
• Fluoroquinolones (like ciprofloxacin) should be avoided in children under 5 years of age except in specific circumstances, and are not indicated for MSSA 3
• The evidence provided focuses heavily on Pseudomonas management, but this patient has MSSA, which requires different antibiotic coverage 1, 4

Address the Stridor Separately

• Stridor in a 5-month-old with CF is unusual and may indicate:
  • Laryngomalacia or tracheomalacia (common in infants)
  • Concurrent viral infection causing croup
  • Airway edema or inflammation
  • Structural airway abnormality
• This requires direct laryngoscopy or flexible bronchoscopy evaluation if stridor persists or worsens 3, 2

Monitoring and Follow-Up

• Obtain repeat respiratory cultures after completing antibiotic therapy to document clearance of MSSA 2, 6
• Monitor for development of Pseudomonas aeruginosa, as this typically emerges later in CF patients and would require different management strategies 6
• If stridor persists beyond treatment of the MSSA infection, pursue imaging and/or bronchoscopy to evaluate for structural abnormalities 3
• Regular surveillance cultures (monthly to quarterly) are recommended in CF patients to detect new pathogens early 2, 6

Age-Specific Considerations

At 5 months of age, this patient is too young for most chronic CF maintenance therapies:

• Inhaled tobramycin, dornase alfa, and hypertonic saline are typically initiated at age 6 years or older 3
• Azithromycin maintenance therapy is also recommended for patients 6 years and older 3
• Focus should be on treating acute infections, optimizing nutrition, and ensuring adequate airway clearance techniques appropriate for infants 2