Bronchiolitis
The most likely diagnosis is D. Bronchiolitis, as this 7-month-old infant presents with the pathognomonic clinical features: low-grade fever, dry cough, bilateral wheezing, tachypnea (RR 47/min), and hyperinflation on chest X-ray following a 3-day prodromal illness—all classic for viral bronchiolitis in this age group. 1
Diagnostic Reasoning
Bronchiolitis is diagnosed clinically based on history and physical examination alone in children aged 1-23 months presenting with acute inflammation of small airways, tachypnea, wheezing and/or crackles following an upper respiratory prodrome, and increased respiratory effort. 1, 2 This infant's presentation is textbook:
- Age 7 months falls squarely within the peak incidence period (most hospitalizations occur in infants <1 year old) 1
- 3-day prodrome of low-grade fever and dry cough represents the typical upper respiratory phase before lower tract involvement 3, 4
- Bilateral wheezing indicates diffuse small airway obstruction from inflammation, edema, and mucus plugging 5, 2
- Tachypnea (RR 47/min) reflects increased work of breathing characteristic of infants 1-12 months with bronchiolitis 1
- Hyperinflation on chest X-ray is pathognomonic, reflecting air trapping from small airway obstruction 1
Why Other Diagnoses Are Incorrect
Asthma (Option A) is extremely unlikely because it is rare as a first presentation at 7 months of age, and the acute febrile illness with 3-day prodrome clearly points to an infectious etiology rather than reactive airway disease. 1 The American Academy of Pediatrics specifically notes that children with recurrent wheezing episodes after the first year of life likely have asthma, but a first episode in an infant under 2 years with viral prodrome is bronchiolitis. 2
Sinusitis (Option B) is incorrect because it does not cause hyperinflation on chest X-ray or bilateral wheezing, and this infant has clear lower respiratory tract involvement with bilateral wheezing and tachypnea—findings incompatible with isolated sinus disease. 1
Influenza (Option C) is less specific because while influenza can cause bronchiolitis, it represents only one of multiple viral etiologies (RSV being most common at 90% of cases), and the clinical presentation is indistinguishable from RSV or other viral causes. 1, 4 The diagnosis is bronchiolitis regardless of specific viral etiology, and routine viral testing is not necessary as it does not change management. 1
Risk Stratification Required
At 7 months, immediately assess for high-risk factors that would indicate potential for severe disease: 1, 6
- Prematurity (especially <32 weeks gestation)
- Chronic lung disease of prematurity
- Hemodynamically significant congenital heart disease
- Neuromuscular disease or immunodeficiency
Infants younger than 12 weeks are at highest risk for severe disease and apnea, though this 7-month-old is past that critical window. 1, 6
Management Approach
Treatment is supportive only—bronchodilators, corticosteroids, and antibiotics do not improve outcomes. 2, 3 The American Academy of Pediatrics strongly recommends against routine antibacterial therapy unless there is strong suspicion of secondary bacterial infection. 5
Key supportive measures include: 2, 3
- Supplemental oxygen only if saturation <90% (continuous pulse oximetry is no longer required) 6, 3
- Nasal suctioning to facilitate breathing and feeding 6
- Adequate hydration via oral, nasogastric, or IV fluids if unable to maintain oral intake 3
Chest X-rays should be reserved for consideration of intubation, unexpected clinical deterioration, or underlying cardiac/pulmonary disorder—they are not necessary for routine diagnosis. 1 This infant already has a chest X-ray showing the characteristic hyperinflation.
Clinical Course and Follow-up
Bronchiolitis is self-limiting, with most children recovering within 2-3 weeks, mean time to cough resolution of 8-15 days, and 90% cough-free by day 21. 1, 6 Children with persistent symptoms beyond 4 weeks may represent post-bronchiolitis syndrome and require reassessment. 1