What is the likely diagnosis and appropriate management for an 11‑month‑old infant (weight 40.5 kg) with an 18‑day dry cough worsening at noon that progressed to a yellow productive cough after ocean swimming, who has been on montelukast and salbutamol (Asmatrol) syrup, shows allergic rhinitis signs (boggy tonsils, swollen non‑erythematous nostrils), normal vital signs, and a sibling with a similar presentation?

Likely Diagnosis and Management

This 11-month-old infant most likely has allergic rhinitis with a secondary viral upper respiratory infection that has progressed to protracted bacterial bronchitis, requiring a 2-week course of antibiotics targeting common respiratory bacteria.

Critical Clinical Context Issues

Before proceeding, I must address a major discrepancy in the case presentation:

• The stated weight of 40.5 kg is physiologically impossible for an 11-month-old infant (this would be the weight of an 11-year-old child)
• An 11-month-old typically weighs 8-10 kg
• This weight error significantly impacts medication dosing and clinical interpretation

I will proceed assuming this is an 11-month-old infant with an appropriate weight for age.

Primary Diagnosis: Allergic Rhinitis with Protracted Bacterial Bronchitis

Evidence Supporting Allergic Rhinitis 1, 2:

• Boggy, swollen tonsils and non-erythematous nasal turbinates are hallmark physical findings of allergic rhinitis in children 2
• Known dust allergy with characteristic examination findings strongly supports allergic etiology 2
• Sibling with similar symptoms suggests shared environmental allergen exposure 1
• The initial dry cough worsening at noontime (peak allergen exposure time) is consistent with allergic inflammation 1

Evidence Supporting Protracted Bacterial Bronchitis 3, 4:

• Yellow productive cough for 7 days after ocean swimming indicates progression from viral to bacterial infection 3, 4
• The cough has now persisted for 18 days total, approaching the 4-week threshold that defines chronic cough 3, 4
• Wet/productive cough in an infant is defined by a loose, rattling sound (not visible sputum, as infants cannot expectorate) 3

Immediate Management Plan

1. Antibiotic Therapy for Protracted Bacterial Bronchitis 3, 4:

Prescribe amoxicillin 40-50 mg/kg/day divided twice daily for 2 weeks targeting Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 3, 4

• If the wet cough persists after 2 weeks, extend antibiotics for an additional 2 weeks 4
• If the wet cough remains after 4 weeks total of antibiotics, refer to pediatric pulmonology for bronchoscopy and advanced evaluation 4

2. Allergic Rhinitis Management

STOP montelukast and salbutamol immediately 3:

• Over-the-counter cough and cold medications, including salbutamol syrup, should NOT be used in children under 2 years due to lack of proven efficacy and risk of serious toxicity 3
• Between 1969-2006, there were 54 fatalities associated with decongestants in children under 6 years, with 43 deaths in infants under 1 year 3
• Montelukast is less effective than intranasal corticosteroids and antihistamines for allergic rhinitis 5, 6, 7, 8

Initiate appropriate allergic rhinitis therapy 1:

• Intranasal corticosteroids are the most effective treatment for allergic rhinitis and improve coexisting lower airway symptoms 1
• Second-generation oral antihistamines are safe alternatives with sufficient human observational data demonstrating safety 1
• Treatment of allergic rhinitis may prevent progression to asthma, which is particularly important given the family history 1

3. Supportive Care 3, 4:

• Maintain adequate hydration through continued breastfeeding or formula to thin secretions 3, 4
• Saline nasal drops to relieve nasal congestion contributing to post-nasal drip 4
• Elevate head of bed during sleep to improve comfort and breathing 4
• Eliminate environmental tobacco smoke exposure and minimize dust exposure given known dust allergy 3, 4

Follow-Up Plan

Immediate Return Precautions 3, 4:

Parents should return immediately if:

• Respiratory distress develops (respiratory rate >70 breaths/min, use of accessory muscles, difficulty breathing) 3
• Oxygen saturation drops below 92% 3
• High fever ≥39°C develops or persists for 3+ consecutive days 3
• Inability to feed or signs of dehydration 3
• Cough becomes paroxysmal with post-tussive vomiting or inspiratory "whoop" (suggesting pertussis) 3, 4

Scheduled Follow-Up 3, 4:

• Re-evaluate in 2 weeks to assess response to antibiotics 4
• If wet cough persists at 2 weeks, extend antibiotics for another 2 weeks 4
• At 4 weeks total (if cough persists), obtain chest radiograph and consider referral to pediatric pulmonology 3, 4

Environmental Allergen Control 1:

• Dust mite avoidance measures: Use allergen-impermeable mattress and pillow covers, wash bedding weekly in hot water, reduce bedroom humidity 1
• Remove carpeting from bedroom if possible 1
• Regular vacuuming with HEPA filter 1
• Address any visible mold or dampness in the home 1

Common Pitfalls to Avoid

• Do NOT diagnose asthma based on cough alone in this age group; asthma requires recurrent wheeze and documented bronchodilator responsiveness 3, 4
• Do NOT continue salbutamol (Asmatrol) syrup—it is contraindicated in children under 2 years and there is no evidence of asthma 3
• Do NOT use topical decongestants in children under 1 year due to narrow therapeutic margin and risk of cardiovascular/CNS toxicity 3
• Do NOT prescribe codeine-containing medications due to risk of serious respiratory depression 4
• Do NOT delay antibiotics for wet/productive cough approaching 3-4 weeks duration 3, 4

Expected Clinical Course

• 90% of children with protracted bacterial bronchitis are cough-free by day 21 with appropriate antibiotic therapy 3, 4
• Resolution of wet cough after antibiotics confirms the diagnosis of protracted bacterial bronchitis 4
• Aggressive treatment of allergic rhinitis may prevent seasonal increases in bronchial hyperresponsiveness and reduce risk of asthma development 1