What are the recommendations for outpatient management of influenza (flu)?

Outpatient Management of Influenza

Start antiviral treatment immediately with oseltamivir 75 mg twice daily for 5 days in all high-risk patients with suspected or confirmed influenza, regardless of symptom duration, and consider treatment in otherwise healthy patients if presenting within 48 hours of symptom onset. 1

Who Should Receive Antiviral Treatment

High-Risk Patients (Treat Immediately, Regardless of Symptom Duration)

The following patients should receive antivirals as soon as possible, even beyond 48 hours of symptom onset 2, 1:

• Age-based risk: Children <2 years and adults ≥65 years 1
• Pregnancy: Pregnant women and those within 2 weeks postpartum 1
• Chronic medical conditions: Patients with cardiac, pulmonary, renal, metabolic, or other chronic diseases 2, 1
• Immunocompromised status: Any degree of immunosuppression 1
• Severe or progressive illness: Any patient with worsening symptoms or requiring hospitalization 2, 1

Otherwise Healthy Patients (Treatment Optional)

For healthy adults and children without risk factors, antiviral treatment may be considered if initiated within 48 hours of symptom onset, with maximum benefit when started within 24 hours. 1, 3 The benefit is modest—approximately 1 day reduction in illness duration—and should be discussed with patients 3, 4. Treatment can reduce antibiotic use (20% vs 38% in untreated patients) by preventing secondary bacterial infections 3.

Recommended Antiviral Medications

First-Line Treatment: Oseltamivir (Tamiflu)

Oseltamivir is the preferred antiviral for outpatient influenza management. 1

Dosing 5:

• Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days
• Children 2 weeks to 12 years: Weight-based dosing using oral suspension (3 mg/kg twice daily for infants <1 year; specific weight-based doses for older children)
• Renal impairment: Reduce dose by 50% if creatinine clearance <30 mL/min 5

Administration: May be taken with or without food, though taking with food reduces nausea 5, 4

Alternative Options

• Zanamivir (Relenza): 10 mg (two 5-mg inhalations) twice daily for 5 days—use for patients who cannot tolerate oseltamivir 1. Caution: Risk of life-threatening bronchospasm; avoid in patients with underlying respiratory disease 6

• Peramivir (Rapivab): Single 600-mg IV infusion for adults unable to absorb oral medication 1

• Baloxavir (Xofluza): Single dose (40-80 mg based on weight) for patients ≥5 years 1, 7. Important: Avoid coadministration with dairy products, calcium-fortified beverages, or supplements containing calcium, iron, magnesium, selenium, or zinc 7

Do not use amantadine or rimantadine due to high resistance rates (>99% of circulating strains) 2

Timing of Treatment Initiation

The earlier treatment is started, the greater the benefit—ideally within 12-24 hours of symptom onset. 8 Starting oseltamivir within 12 hours of fever onset reduces illness duration by 3.1 days compared to starting at 48 hours 8. However, treatment initiated even after 48 hours still provides benefit in high-risk patients by reducing viral shedding and potentially preventing complications 9.

Supportive Care

Provide the following alongside antiviral therapy 1:

• Hydration: Ensure adequate fluid intake
• Fever management: Acetaminophen or ibuprofen for symptom relief
• Isolation: Rest at home and avoid contact with others to prevent transmission

Do not use corticosteroids for influenza treatment unless indicated for other medical conditions 1

Monitoring and Red Flags

Expected Clinical Course

• Fever duration: Typically resolves within 3-5 days with appropriate treatment 10
• Clinical improvement: Should occur within 48 hours of starting antivirals 2, 10

When to Reassess

Patients should return for re-evaluation if 2, 1, 10:

• Fever persists beyond 4-5 days without improvement
• Fever recurs after initial improvement (suggests bacterial superinfection)
• Clinical deterioration at any point
• No improvement after 3-5 days of antiviral treatment

In these cases, investigate and empirically treat for bacterial co-infection (particularly pneumonia) with appropriate antibiotics 1, 3

Vital Sign Instability

Monitor for development of 10:

• Temperature >37.8°C beyond expected timeframe
• Respiratory rate >24/min
• Oxygen saturation <90%
• Heart rate >100/min
• Systolic blood pressure <90 mmHg

Special Populations

Immunocompromised Patients

• Consider resistance testing if persistent viral replication despite treatment 1
• May require prolonged prophylaxis (up to 12 weeks during community outbreaks) 5
• May not mount adequate febrile response—treat based on clinical suspicion even without documented fever 2

Elderly Patients

• May have atypical presentations without fever 10
• Warrant closer monitoring due to higher complication risk 10

Antiviral Prophylaxis

Consider post-exposure prophylaxis with oseltamivir 75 mg once daily for 10 days in high-risk patients following close contact with confirmed influenza, especially if 1:

• Influenza vaccine is contraindicated
• Within 2 weeks after vaccination (before optimal immunity develops)
• During community outbreaks in high-risk settings

Key Clinical Pitfalls to Avoid

1. Don't wait for laboratory confirmation to start treatment in high-risk patients—clinical diagnosis is sufficient 2, 11
2. Don't withhold treatment beyond 48 hours in high-risk patients—they still benefit from antivirals 1, 9
3. Don't use rapid antigen tests alone for diagnosis if testing is needed—rapid molecular assays are preferred for accuracy 11
4. Monitor local resistance patterns—antiviral susceptibility can change over time 2
5. Don't forget that most flu-like illnesses are not influenza—consider alternative diagnoses if patients fail to improve 6