When is acute sinusitis most likely to develop and what clinical criteria indicate that antibiotics are warranted?

When Antibiotics Are Indicated for Acute Sinusitis

Antibiotics should be prescribed only when acute bacterial rhinosinusitis is confirmed by meeting at least one of three specific clinical patterns: persistent symptoms ≥10 days without improvement, severe symptoms for ≥3–4 consecutive days, or "double sickening" (worsening after initial improvement). 1, 2

Diagnostic Criteria for Bacterial Sinusitis

Pattern 1: Persistent Symptoms (≥10 Days)

• Purulent nasal discharge (thick, colored, not clear) plus either nasal obstruction/congestion or facial pain/pressure/fullness lasting ≥10 days without any sign of improvement. 1, 2
• This is the most common presentation warranting antibiotics, as approximately 98–99.5% of acute rhinosinusitis cases are viral and resolve spontaneously within 7–10 days. 1, 3
• Symptoms lasting <10 days are almost always viral and do not require antibiotics unless severe features are present. 1, 3

Pattern 2: Severe Symptoms (≥3–4 Consecutive Days)

• High fever ≥39°C (102.2°F) with purulent nasal discharge and facial pain for at least 3–4 consecutive days at the onset of illness. 1, 2
• This pattern indicates immediate antibiotic therapy without waiting for the 10-day threshold. 2

Pattern 3: "Double Sickening" (Worsening After Initial Improvement)

• Initial improvement from a viral upper respiratory infection followed by new-onset fever, worsening nasal discharge, or substantially increased cough within 10 days. 1, 2
• This biphasic pattern strongly suggests bacterial superinfection and warrants antibiotics regardless of total symptom duration. 2

Key Clinical Features That Increase Likelihood of Bacterial Infection

• Unilateral maxillary tooth pain or facial pain that worsens when bending forward (suggests maxillary sinusitis). 1
• Persistent purulent nasal discharge ≥7 days combined with maxillary tooth pain or unilateral facial pain. 3
• Unilateral sinus tenderness on physical examination. 3
• Purulent conjunctivitis occurring together with sinusitis symptoms (French guidelines recognize this as a strong bacterial indicator). 3

Critical Pitfalls: When NOT to Prescribe Antibiotics

• Purulent nasal discharge alone does not indicate bacterial infection—it reflects neutrophilic inflammation common to viral disease. 3
• Symptom duration <10 days without severe features (fever ≥39°C with purulent discharge for ≥3 days) should be managed with symptomatic treatment only. 1, 3
• Mucus color alone (yellow or green) should not determine antibiotic need, as color reflects neutrophils, not bacteria. 3
• Radiographic findings (CT or X-ray) should not be used to diagnose uncomplicated acute bacterial sinusitis, as up to 87% of viral upper respiratory infections show sinus abnormalities on imaging. 3

Watchful Waiting as an Alternative Strategy

• For patients meeting the persistent symptoms criterion (≥10 days), either immediate antibiotics or watchful waiting for an additional 3–7 days is appropriate when reliable follow-up can be ensured. 1, 2
• Approximately 73–85% of patients improve spontaneously by 7–15 days without antibiotics, even when bacterial infection is present. 2
• The number needed to treat (NNT) with antibiotics is 10–15 to achieve one additional cure compared with placebo. 3, 2
• Start antibiotics only if no improvement by day 7 or if symptoms worsen at any time during observation. 3

First-Line Antibiotic Regimen When Indicated

• Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5–10 days provides 90–92% predicted clinical efficacy against the major pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis). 1, 3, 2
• High-dose regimen (2 g/125 mg twice daily) is indicated for patients with recent antibiotic use (past 4–6 weeks), age >65 years, daycare exposure, moderate-to-severe symptoms, or comorbidities. 3
• Treatment duration: 5–10 days or until symptom-free for 7 consecutive days (typically 10–14 days total); recent evidence supports shorter 5–7 day courses with comparable efficacy and fewer adverse effects. 3, 4

Essential Adjunctive Therapies (Add to All Patients)

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily significantly reduce mucosal inflammation and accelerate symptom resolution—supported by strong evidence from multiple randomized controlled trials. 1, 3, 2
• Saline nasal irrigation 2–3 times daily provides symptomatic relief and aids mucus clearance. 3, 2
• Analgesics (acetaminophen or ibuprofen) for pain and fever control. 3, 2

Monitoring and Reassessment Protocol

• Reassess at 3–5 days: If no clinical improvement (persistent purulent drainage, unchanged facial pain, or worsening), switch to high-dose amoxicillin-clavulanate or a respiratory fluoroquinolone. 3
• Reassess at 7 days: Persistent or worsening symptoms warrant confirmation of diagnosis, exclusion of complications (orbital cellulitis, meningitis), and consideration of imaging or ENT referral. 3
• Red-flag symptoms requiring urgent evaluation at any time: severe headache, visual changes, periorbital swelling, altered mental status, or worsening despite appropriate therapy. 3

Special Pediatric Considerations

• Children require the same three diagnostic patterns (persistent ≥10 days, severe ≥3–4 days, or double sickening) before prescribing antibiotics. 2
• Pediatric dosing: Amoxicillin 45 mg/kg/day (standard) or 80–90 mg/kg/day (high-dose for risk factors such as age <2 years, daycare attendance, or recent antibiotic use) divided twice daily. 3, 2
• Treatment duration: Minimum 10–14 days for children (longer than adult courses). 3
• Reassess at 72 hours: If no improvement or worsening, switch to high-dose amoxicillin-clavulanate. 3