What investigations should be done for a baby presenting with cough and fever?

Investigations for a Baby Presenting with Cough and Fever

A chest radiograph should be obtained in all febrile babies with cough who are under 3 months of age, while for older infants, radiography should be guided by specific clinical findings such as tachypnea, respiratory distress, or high fever (>39°C) with elevated WBC count. 1

Age-Based Approach to Investigation

Infants Under 3 Months

• Chest radiograph: Required for all febrile infants under 3 months with any signs of respiratory illness 1
• Complete blood count: To evaluate for leukocytosis
• Blood culture: To rule out bacteremia
• Urinalysis and urine culture: Essential as urinary tract infections are common in this age group

Infants 3 Months to 2 Years

Chest radiography should be considered when the following are present:

• Fever ≥39°C (102.2°F) with WBC count >20,000/mm³ 1
• Tachypnea (respiratory rate >50/min) 1
• Chest recession or indrawing 1
• Rales/crackles on auscultation 1
• Decreased breath sounds 1
• Hypoxia 1
• Fever duration >48 hours 1
• Tachycardia and tachypnea out of proportion to fever 1

Clinical Findings That Increase Likelihood of Pneumonia

The presence of the following significantly increases the likelihood of pneumonia:

• Tachypnea (sensitivity 73.8%, specificity 76.8%) 1
• Crackles (strongest univariate predictor) 1
• Respiratory distress 1
• Decreased breath sounds 1
• Fever >38.5°C with chest recession and respiratory rate >50/min (in children up to 3 years) 1

When to Avoid Chest Radiography

Chest radiography is usually NOT indicated in:

• Febrile children >3 months with temperature <39°C without clinical evidence of acute pulmonary disease 1
• Children with wheezing or high likelihood of bronchiolitis 1
• Children where the clinical diagnosis is clear and uncomplicated 1

Additional Investigations to Consider

• C-reactive protein (CRP): More predictive of serious bacterial infection than WBC count, especially when fever has been present >12 hours 2
• Urinalysis and urine culture: Particularly important as UTIs are common in febrile young children without an obvious source of infection 1
• Pulse oximetry: To detect hypoxia, which is an indication for chest radiography 1

Important Clinical Considerations

1. Timing matters: Bacterial markers (WBC, ANC, CRP) are more predictive of serious bacterial infection if fever duration is >12 hours 2

2. Occult pneumonia: Consider chest radiography in highly febrile children (>39°C) with leukocytosis (>20,000/mm³) even without respiratory signs, as studies show pneumonia can be detected in about 26% of such cases 1

3. Collection method for urine samples: Contamination rates vary significantly by collection method: 26% for clean catch, 12% for catheter specimens, and only 1% for suprapubic aspiration 1

Follow-up Considerations

• Follow-up radiographs are indicated for children with:
  • Lobar collapse
  • Round pneumonia (to ensure no missed tumors)
  • Persistent symptoms despite appropriate treatment 1

By following this structured approach to investigating babies with cough and fever, clinicians can appropriately identify those requiring chest radiography while avoiding unnecessary imaging in others, balancing diagnostic accuracy with concerns about radiation exposure.