Management of Influenza B Positive Fever and Cold
For influenza B positive patients with fever and cold symptoms, initiate oseltamivir 75 mg orally twice daily for 5 days if the patient presents within 48 hours of symptom onset and has fever >38°C. 1, 2
Antiviral Treatment: Oseltamivir
Eligibility Criteria
Dosing by Age and Weight
Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days 1, 2
Children ≥12 months: 1
- ≤15 kg: 30 mg twice daily
15-23 kg: 45 mg twice daily
23-40 kg: 60 mg twice daily
40 kg: 75 mg twice daily
Infants 9-11 months: 3.5 mg/kg per dose twice daily 1
Term infants 0-8 months: 3 mg/kg per dose twice daily 1
Special Circumstances for Antiviral Use
- Immunocompromised or elderly patients unable to mount adequate fever response may still benefit from oseltamivir despite lack of documented fever 1
- Severely ill hospitalized patients, particularly if immunocompromised, may benefit from oseltamivir started >48 hours after symptom onset, though evidence is limited 1, 3
Expected Benefits
Oseltamivir reduces illness duration by approximately 24 hours (1 day), decreases symptom severity by up to 38%, and may reduce hospitalizations and subsequent antibiotic use 1, 4, 5. Earlier initiation within 12 hours of fever onset provides maximum benefit, reducing illness duration by 3.1 days compared to treatment at 48 hours 5.
Adverse Effects and Management
- Most common side effect is nausea (10% of patients), which can be managed with mild antiemetics 1
- Taking oseltamivir with food significantly improves tolerability and reduces gastrointestinal symptoms 4, 5
- Other side effects include vomiting, headache, and diarrhea 1
Renal Dosing Adjustment
Reduce dose by 50% (75 mg once daily) if creatinine clearance <30 mL/minute 1
Antibiotic Management: When NOT to Use
Previously Healthy Patients Without Pneumonia
Do NOT routinely prescribe antibiotics for uncomplicated influenza B with cold symptoms and acute bronchitis 1, 6, 3. Features like cough, retrosternal discomfort, wheeze, and sputum production are integral parts of influenza illness and do not indicate bacterial infection 1.
When to CONSIDER Antibiotics
- Recrudescent fever (fever returns after initial improvement)
- Increasing breathlessness or dyspnea
- New focal chest signs suggesting pneumonia
- High-risk patients (COPD, chronic cardiac disease, immunocompromised) with lower respiratory tract features
Antibiotic Selection IF Indicated
First-line oral choices: 1, 6, 3
- Co-amoxiclav (preferred)
- Tetracycline (e.g., doxycycline)
Alternative for penicillin intolerance: 1
- Macrolide (clarithromycin preferred over azithromycin due to better H. influenzae activity)
Supportive Care
Symptomatic Management
- Antipyretics for fever control (avoid aspirin in children due to Reye's syndrome risk) 3
- Adequate hydration 3
- Rest and monitoring of symptoms 1
Delayed Antibiotic Prescription Strategy
For selected previously healthy patients, consider providing a delayed antibiotic prescription with clear instructions to use only if: 1
- Illness not settling after 2 days
- Worsening of symptoms occurs
- This minimizes unnecessary antibiotic use while reducing reconsultation rates 1
Common Pitfalls to Avoid
- Do not prescribe antibiotics reflexively for influenza B with cold symptoms - this is viral and antibiotics provide no benefit in uncomplicated cases 6, 3
- Do not delay oseltamivir beyond 48 hours in eligible patients - efficacy decreases significantly with delayed initiation 5
- Do not withhold oseltamivir from immunocompromised or elderly patients lacking documented fever - they may still benefit 1
- Watch for secondary bacterial pneumonia, which typically develops 4-5 days after initial influenza symptoms, not at initial presentation 6