When should antibiotics be started in a child with an acute lower respiratory tract infection, including the clinical criteria and high‑risk groups that indicate bacterial involvement?

When to Start Antibiotics in Children with Lower Respiratory Tract Infection

Do Not Routinely Prescribe Antibiotics for Preschool-Aged Children

Young children presenting with mild symptoms of lower respiratory tract infection need not be treated with antibiotics, as viral pathogens are responsible for the great majority of clinical disease in preschool-aged children. 1

The evidence strongly supports withholding antibiotics in most cases of LRTI in children under 5 years, since these infections are predominantly viral. 1, 2 A recent randomized controlled trial demonstrated that amoxicillin provided no clinical benefit over placebo for uncomplicated LRTI in children aged 1-12 years, with similar symptom duration, reconsultation rates, and complications in both groups. 3

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Clinical Criteria Indicating Need for Antibiotics

Age-Based Approach

For children under 5 years:

• Antibiotics are indicated only when bacterial pneumonia is suspected based on specific clinical and radiographic findings 1
• Amoxicillin is the first-line choice at 80-100 mg/kg/day in three divided doses when bacterial infection is likely 1, 4

For school-aged children (≥5 years):

• Consider both typical bacterial pathogens (S. pneumoniae) and atypical organisms (Mycoplasma, Chlamydophila) 1
• Macrolide antibiotics should be prescribed when atypical pathogens are suspected, particularly in school-aged children and adolescents 1

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Specific Clinical Indicators for Bacterial Infection

Respiratory Rate Thresholds

Tachypnea is the single most reliable indicator for antibiotic initiation:

• Infants: Respiratory rate >70 breaths/min indicates need for hospital admission and antibiotics 1
• Older children: Respiratory rate >50 breaths/min indicates need for hospital admission and antibiotics 1
• Primary care setting: Respiratory rate >40-50 breaths/min is the best indicator for starting antibiotic treatment 5

Severity Markers Requiring Immediate Antibiotics

• Oxygen saturation ≤92% on room air 1
• Chest indrawing (subcostal or intercostal retractions) - this is a reliable indication for hospital admission and antibiotic therapy 5
• Grunting respirations 1
• Cyanosis 1
• Difficulty breathing with increased work of breathing 1

Additional Clinical Features Suggesting Bacterial Etiology

• High fever ≥39°C (103°F) for ≥3 consecutive days with purulent nasal discharge or facial pain 6
• Age >6 months combined with fever and elevated WBC increases likelihood of bacterial infection 6
• Not feeding or signs of dehydration 1
• Intermittent apnea in infants 1

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Radiographic Criteria (When Available)

A scoring system can help distinguish bacterial from viral etiology: 6

Features suggesting bacterial pneumonia (assign positive scores):

• Well-defined pulmonary infiltrates involving mid or peripheral portions of only one lobe 6
• Pleural effusion 6
• Abscess or pneumatocele formation 6

Features suggesting viral infection (assign negative scores):

• Poorly defined infiltrates, often perihilar, involving more than one lobe 6
• Atelectasis involving right middle lobe, right upper lobe, or multiple sites 6

A score of 0 or less has 95% predictive value for viral pneumonia, while positive scores have 70% predictive value for bacterial etiology. 6

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High-Risk Groups Requiring Lower Threshold for Antibiotics

Start antibiotics more readily in children with:

• Incomplete immunization against Haemophilus influenzae type b or Streptococcus pneumoniae 1, 4
• Coexistent purulent acute otitis media 4
• Recent antibiotic use (within 4-6 weeks) 4
• Life-threatening infection or empyema 1
• Inability to absorb oral medications (vomiting) - use IV antibiotics 1

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Antibiotic Selection Algorithm

First-Line Therapy

Amoxicillin 80-100 mg/kg/day divided into three daily doses (maximum 3 g/day) for children <30 kg with suspected bacterial pneumonia 1, 4

Alternative Regimens

• Amoxicillin-clavulanate: For children with risk factors (insufficient vaccination, purulent otitis media, recent antibiotic use) 1, 4
• Macrolides (azithromycin 10 mg/kg day 1, then 5 mg/kg/day days 2-5): For school-aged children when atypical pathogens suspected, or for beta-lactam allergy 1, 4
• IV therapy (ampicillin, ceftriaxone, or cefotaxime): For hospitalized children unable to take oral medications or with severe disease 1

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Reassessment Timeline

Evaluate therapeutic efficacy after 48-72 hours of treatment: 1, 4

• Primary assessment criterion is fever resolution 4
• Apyrexia often achieved in <24 hours with pneumococcal pneumonia 4
• If no improvement after 48-72 hours: Perform clinical and radiological reassessment, consider atypical bacteria and switch to macrolide therapy 1, 4
• If worsening or no improvement after 5 days: Consider hospitalization 4

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Critical Pitfalls to Avoid

• Do not use fever alone as an indicator for antibiotics - it is a poor guide to bacterial etiology 5
• Do not prescribe antibiotics for bronchiolitis - this is a viral infection requiring only supportive care 2
• Do not perform routine chest X-rays for children well enough for outpatient management 2
• Avoid chest physiotherapy - it is not beneficial and should not be performed 1
• Recognize that cough may persist longer than other symptoms and should not be used as sole indicator of treatment failure 4