Management of Influenza
Oseltamivir is the preferred antiviral for treating severe influenza and for post-exposure prophylaxis, with treatment ideally initiated within 48 hours of symptom onset to reduce morbidity and mortality. 1
Antiviral Treatment
When to Treat
Initiate antiviral therapy promptly in:
- Severe influenza (hospitalized patients, respiratory distress, pneumonia) - treat immediately, even beyond 48 hours 1, 2
- High-risk patients with non-severe disease within 48 hours of symptom onset 1, 3
- Chronic conditions (asthma, COPD, diabetes, heart disease, neurologic disorders)
- Immunocompromised patients
- Children <2 years, adults ≥65 years
- Pregnant women
Do not delay treatment while awaiting test results - clinical judgment based on symptoms and local influenza activity should guide immediate therapy 1, 2
Drug Selection and Dosing
Oseltamivir (preferred agent):
- Adults: 75 mg twice daily for 5 days 1, 4
- Children ≥12 months:
- ≤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 1
- Infants 9-11 months: 3.5 mg/kg/dose twice daily 1
- Term infants 0-8 months: 3 mg/kg/dose twice daily 1
- Renal impairment: Reduce dose by 50% if creatinine clearance <30 mL/min 4
Baloxavir is conditionally recommended for high-risk non-severe cases within 48 hours, but is NOT recommended for routine non-severe cases without risk factors 3, 5
Zanamivir: 10 mg (two 5-mg inhalations) twice daily for 5 days - alternative for patients ≥7 years, but avoid in those with underlying airway disease due to bronchospasm risk 1
Critical Treatment Principles
- Severely ill or immunocompromised hospitalized patients may benefit from treatment started >48 hours after onset, despite lack of definitive evidence 4, 2
- Do NOT use combination antiviral therapy - no evidence of benefit and may promote resistance 5
- Continue treatment for full 5-day course regardless of clinical improvement 1, 4
Post-Exposure Prophylaxis
Oseltamivir is the preferred prophylaxis agent 1
Indications for Chemoprophylaxis
Initiate within 48 hours of exposure for:
- High-risk individuals exposed to confirmed influenza who cannot be vaccinated 1, 6
- High-risk individuals during the 2-week period after influenza vaccination 1, 6
- Unimmunized healthcare workers or family members with ongoing close exposure to high-risk patients 1, 6
- Anyone exposed to zoonotic (avian) influenza viruses - regardless of individual risk 3, 5
- Outbreak control in institutional settings 1, 6
Prophylaxis Dosing
Oseltamivir:
- Adults: 75 mg once daily for 7 days after last exposure 1
- Children: Same weight-based dosing as treatment, but once daily 1
Critical caveat: Chemoprophylaxis is NOT a substitute for vaccination 1, 6
Diagnostic Testing Strategy
Outpatients
Test when results will influence management:
- High-risk patients with influenza-like illness 1, 2
- Patients where positive result would avoid unnecessary antibiotics or additional testing 1, 2
- Use nasopharyngeal specimens (highest sensitivity) 2
- Molecular assays (RT-PCR/NAAT) or digital immunoassays preferred over rapid antigen tests 1, 3
Critical pitfall: Rapid antigen tests have low sensitivity - negative results should NOT rule out influenza or guide treatment decisions 1, 6
Hospitalized Patients
Test ALL patients requiring hospitalization with:
- Acute respiratory illness with or without fever 2
- Acute exacerbation of chronic cardiopulmonary disease 2
- Immunocompromised patients with respiratory symptoms 2
Use high-sensitivity molecular assays (RT-PCR) for hospitalized patients 1, 2
Supportive Care
Monitoring (Hospitalized Patients)
Monitor at least twice daily (more frequently if severe):
- Temperature, respiratory rate, pulse, blood pressure
- Mental status, oxygen saturation, inspired oxygen concentration
- Early Warning Score systems facilitate systematic monitoring 4
Respiratory Support
- Supplemental oxygen to maintain SpO₂ ≥90% 4
- Non-invasive ventilation may bridge to invasive ventilation when ICU beds limited, but requires experienced units with proper infection control 4
- Invasive mechanical ventilation for respiratory failure 4
Additional Supportive Measures
- Assess for volume depletion and cardiac complications - provide IV fluids as needed 4
- Nutritional support in severe or prolonged illness 4
- Antipyretics and analgesics for symptom relief
Antibiotic Use
Do NOT routinely prescribe antibiotics for uncomplicated influenza - strong recommendation 4, 3
When to Consider Antibiotics
Add antibiotics if:
- Clinical evidence of bacterial pneumonia (infiltrate on imaging, persistent fever, purulent sputum) 4
- Worsening symptoms after initial improvement (recrudescent fever, increasing dyspnea) 4
- High-risk patients with lower respiratory tract features 4
Antibiotic Selection
Non-severe pneumonia (oral):
- Co-amoxiclav or tetracycline (doxycycline) - preferred 4
- Macrolide (clarithromycin) or respiratory fluoroquinolone - alternative 4
Severe pneumonia (parenteral):
- IV co-amoxiclav or 2nd/3rd generation cephalosporin (cefuroxime, cefotaxime) PLUS macrolide 4
- Alternative: Respiratory fluoroquinolone plus β-lactam 4
Target coverage: Streptococcus pneumoniae and Staphylococcus aureus 4
Adjunctive Therapies NOT Recommended
Strong evidence AGAINST use in influenza:
- Corticosteroids - conditional recommendation against in severe influenza 3, 5
- Macrolide antibiotics (without bacterial co-infection) 3, 5
- mTOR inhibitors 3, 5
- NSAIDs 3, 5
- Convalescent plasma/passive immune therapy 3, 5
Discharge Criteria
Consider continued hospitalization if ≥2 of the following present 24 hours before planned discharge:
- Temperature >37.8°C
- Heart rate >100/min
- Respiratory rate >24/min
- Systolic BP <90 mmHg
- Oxygen saturation <90%
- Inability to maintain oral intake
- Abnormal mental status 4
Arrange follow-up for patients with significant complications or worsening of underlying disease 4