What are the possible causes of a 2-month-old female infant's cough for 10 days and wheezing for 2 days, with no history of fever, a slight decrease in oral intake, and sleepiness?

Differential Diagnosis for 2-Month-Old with Cough and Wheezing

The most likely diagnosis in this 2-month-old infant with 10 days of cough, 2 days of wheezing, no fever, decreased oral intake, and lethargy is acute viral bronchiolitis, which is the most common lower respiratory tract infection in this age group and typically presents with these exact symptoms. 1

Primary Diagnosis: Acute Viral Bronchiolitis

Bronchiolitis is characterized by rhinitis, tachypnea, wheezing, cough, crackles, use of accessory muscles, and/or nasal flaring in infants 1 month to 2 years of age. 1 The clinical presentation described—progressive cough followed by wheezing, decreased feeding, and lethargy—fits the classic pattern of viral bronchiolitis. 1

Key Supporting Features:

• Age: At 2 months, this infant falls within the peak age range for bronchiolitis, with 90% of children infected with RSV in the first 2 years of life. 1
• Symptom progression: The typical pattern shows upper respiratory symptoms (cough) progressing to lower respiratory involvement (wheezing) over days. 1
• Absence of fever: While fever can occur, its absence does not exclude bronchiolitis. 1
• Decreased oral intake and lethargy: These are concerning signs indicating moderate to severe disease requiring urgent evaluation. 1

Viral Pathogens to Consider:

• Respiratory syncytial virus (RSV) - most common cause 1
• Human metapneumovirus 1
• Influenza 1
• Parainfluenza 1
• Rhinovirus 2

Alternative Diagnoses to Consider

1. Pertussis (Whooping Cough)

At 2 months of age, the infant may not have completed the primary vaccination series, making pertussis a critical consideration. 1 Look for:

• Paroxysmal coughing episodes 1
• Post-tussive vomiting 1
• Apneic episodes (especially concerning given the lethargy) 1
• Absence of fever is typical in pertussis 1

2. Bacterial Pneumonia (Secondary)

While less common as a primary diagnosis, consider if: 3

• High fever develops (≥38.5°C for >3 days) 4
• Respiratory distress worsens 5
• Purulent nasal discharge with high fever present 5

3. Mycoplasma Pneumoniae

Less likely at 2 months but possible: 3

• More common in school-aged children 3
• Typically presents with progressive onset of fever, headaches, and cough 3
• Crackles on auscultation 3

4. Congenital Anatomic Abnormalities

Given the age and persistent symptoms, consider: 1

• Vascular ring 1
• Tracheomalacia 1
• Congenital heart disease 1

5. Aspiration (Gastroesophageal Reflux)

Evaluate for: 6

• Coughing with feeding 4
• Recurrent regurgitation 4
• Poor weight gain 4

Critical Red Flags Requiring Immediate Evaluation

This infant requires urgent assessment given the combination of decreased oral intake and lethargy, which may indicate impending respiratory failure or dehydration. 1

Immediate concerns:

• Apnea risk: Infants under 3 months with bronchiolitis are at highest risk for apneic episodes 1
• Dehydration: Decreased oral intake for 2 days in a 2-month-old is concerning 1
• Altered mental status: Lethargy may indicate hypoxia, hypercarbia, or sepsis 1
• Respiratory distress: Assess for tachypnea, retractions, nasal flaring, grunting 1

Signs requiring hospitalization:

• Persistent increased respiratory effort 1
• Apnea 1
• Need for intravenous hydration 1
• Supplemental oxygen requirement 1
• Inability to maintain adequate oral intake 1

Diagnostic Approach

Essential Clinical Assessment:

• Respiratory rate: Tachypnea is a key finding in bronchiolitis 1
• Work of breathing: Look for retractions, nasal flaring, grunting 1
• Oxygen saturation: Measure SpO2 to assess severity 1
• Hydration status: Assess mucous membranes, urine output, fontanelle 1
• Auscultation: Listen for wheezing, crackles, decreased air entry 1

Investigations to Consider:

• Chest radiograph: Not routinely needed for typical bronchiolitis but consider if atypical features, severe disease, or diagnostic uncertainty 1
• Viral testing: RSV testing may guide cohorting decisions if hospitalization needed 1
• Pertussis testing: Nasopharyngeal swab for PCR if clinical suspicion 1
• Complete blood count: Not routinely indicated unless bacterial infection suspected 1

Management Principles

For bronchiolitis, treatment is supportive only—no medications have proven efficacy. 1

Supportive Care:

• Hydration: Ensure adequate fluid intake; IV fluids if unable to feed orally 1
• Oxygen: Supplemental oxygen if SpO2 persistently <90% 1
• Nasal suctioning: Gentle suction to clear secretions before feeds 5
• Monitoring: Close observation for apnea, worsening respiratory distress 1

What NOT to Do:

• DO NOT use bronchodilators: No proven benefit in bronchiolitis 1
• DO NOT use corticosteroids: Not effective for acute bronchiolitis 1
• DO NOT use antibiotics: Unless secondary bacterial infection confirmed 1, 7
• DO NOT use cough medications: No role in infants and potentially harmful 4
• DO NOT give honey: Contraindicated under 12 months due to botulism risk 4

Follow-Up Considerations

Most children with bronchiolitis are cough-free by day 21, with mean cough resolution at 8-15 days. 1 If cough persists beyond 4 weeks, re-evaluate according to pediatric chronic cough protocols. 1, 4

When to Re-evaluate:

• Symptoms not improving after 48 hours 4
• Cough persisting beyond 2-4 weeks 4
• Development of new symptoms 4
• Worsening respiratory distress 5