Viral vs. Bacterial Upper Respiratory Infections in the First 7 Days
The vast majority—approximately 98–99.5%—of upper respiratory infections in the first 7 days are viral in origin, with only 0.5–2% progressing to bacterial superinfection. 1
Epidemiologic Data
Viral URIs dominate the clinical landscape:
- Adults experience 2–5 viral upper respiratory infections per year, while school-aged children suffer 7–10 episodes annually 1
- Up to 90% of viral URIs show CT evidence of sinus mucosal involvement, yet these resolve spontaneously within 21 days without antibiotics 1
- Over 90% of acute respiratory infections presenting in the first week are caused by respiratory viruses (rhinovirus, influenza A/B, parainfluenza, RSV, coronavirus, adenovirus) 2, 3
Bacterial complications are rare in the first week:
- Only 0.5–2% of viral upper respiratory tract infections become complicated by bacterial superinfection 1
- The European Position Paper on Rhinosinusitis (EPOS 2020) explicitly states that "only a minority of acute rhinosinusitis is from bacterial origin" 1
- Bacterial sinusitis typically develops after day 5–10, not during the initial viral phase 1
Clinical Timeline and Diagnostic Criteria
The first 7 days represent the viral phase:
- Most viral URI symptoms resolve by day 5, with nasal discharge and cough potentially lasting until day 10–14 1
- Acute bacterial rhinosinusitis should be suspected only when symptoms increase after 5 days or persist beyond 10 days 1
- Post-viral acute rhinosinusitis is diagnosed when symptoms worsen after initial improvement ("double sickening") or fail to improve after 10 days 1
Bacterial infection within the first 7 days requires at least 3 of these 5 criteria:
- Discolored (purulent) mucus
- Severe unilateral facial pain
- Fever >38°C
- Elevated inflammatory markers (CRP/ESR)
- "Double sickening" pattern (worsening after initial improvement) 1
Critical Clinical Pitfall
Purulent nasal discharge does NOT indicate bacterial infection in the first week. Green or yellow sputum reflects inflammatory cells and sloughed epithelium from the viral infection itself, not bacterial superinfection 2. This is one of the most common reasons for inappropriate antibiotic prescribing in viral URIs 3.
Age-Specific Considerations
Children have higher viral URI frequency but similar bacterial complication rates:
- Children aged 0–4 years: 5.0–7.95 respiratory illnesses per year 1
- Children aged 10–14 years: 2.4–5.02 respiratory illnesses per year 1
- The 0.5–2% bacterial complication rate applies across all age groups 1
Management Implications
Antibiotics are not indicated for URIs in the first 7 days unless specific bacterial criteria are met:
- The overwhelming viral etiology (98–99.5%) means empiric antibiotics expose patients to adverse effects without benefit 2, 3
- When antibiotics are prescribed for acute bronchitis (a lower respiratory manifestation), they reduce cough duration by only 0.5 days 2
- Supportive care with symptom-directed therapy remains the evidence-based approach for the first 7–10 days 2, 3