What is the treatment for a high-risk patient with suspected Influenza B?

Treatment of High-Risk Patients with Suspected Influenza B

Start oseltamivir 75 mg orally twice daily for 5 days immediately upon suspicion of influenza B in any high-risk patient, without waiting for diagnostic confirmation and regardless of symptom duration. 1, 2

Immediate Antiviral Treatment Indications

High-risk patients requiring immediate empiric treatment include:

• Children younger than 2 years of age 1, 3
• Adults ≥65 years of age 1, 3
• Pregnant women and those within 2 weeks postpartum 1, 3
• Immunocompromised patients (HIV infection, malignancy, chemotherapy, chronic steroid use >20 mg prednisolone daily for >1 month, asplenia) 1
• Patients with chronic medical conditions:
  • Chronic respiratory disease (asthma requiring inhaled steroids, COPD, cystic fibrosis, bronchiectasis) 1
  • Chronic heart disease (congenital heart disease, heart failure, ischemic heart disease requiring medication) 1
  • Chronic renal disease (nephrotic syndrome, renal failure, transplant recipients) 1
  • Chronic liver disease (cirrhosis) 1
  • Diabetes mellitus requiring insulin or oral hypoglycemics 1
  • Neurological diseases with muscle weakness or cerebral palsy 1
  • Hemoglobinopathies 1
• Residents of long-stay residential care facilities 1

Antiviral Medication Selection

Oseltamivir is the preferred first-line agent for influenza B because it has proven efficacy against both influenza A and B, unlike amantadine and rimantadine which only work against influenza A. 1, 2, 4

• Standard dosing: Oseltamivir 75 mg orally twice daily for 5 days in adults 1, 2, 4
• Alternative agents: Zanamivir (inhaled) or peramivir (intravenous single dose) are acceptable alternatives 1, 3
• Do not use combination neuraminidase inhibitors 1
• Do not use higher than FDA-approved doses routinely 1

Critical Timing Considerations

Treatment should begin as soon as possible, ideally within 48 hours of symptom onset, but should NOT be withheld in high-risk patients even if >48 hours have elapsed. 1, 2, 3, 5

• Treatment reduces illness duration by 17.6-29.9 hours and decreases pneumonia risk by 50% when started within 48 hours 2
• In high-risk patients, zanamivir reduced symptom duration by 2.5 days and reduced antibiotic-requiring complications by 43% 6
• Severely ill or hospitalized patients benefit from treatment regardless of illness duration 1, 5

Extended Treatment Duration Considerations

Consider extending antiviral treatment beyond 5 days for:

• Immunocompromised patients with documented or suspected prolonged viral replication 1
• Hospitalized patients with severe lower respiratory tract disease, pneumonia, or ARDS 1

Managing Bacterial Coinfection

Empirically add antibiotics to antiviral therapy when:

• Patient presents initially with severe disease (extensive pneumonia, respiratory failure, hypotension, persistent fever) 1, 3
• Patient deteriorates after initial improvement, particularly while on antivirals 1, 3
• Patient fails to improve after 3-5 days of antiviral treatment 1, 3

The IDSA recommends investigating bacterial coinfection in these scenarios because secondary bacterial pneumonia (commonly Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae) is a major cause of influenza-related mortality. 1

Diagnostic Testing Approach

Use RT-PCR or other molecular assays for diagnosis, not rapid antigen tests. 1, 3

• Rapid influenza diagnostic tests (RIDTs) have poor sensitivity and should not be used in hospitalized or high-risk patients 1
• Negative RIDT results require confirmation with RT-PCR 1
• Do not delay treatment while awaiting test results in high-risk patients 1, 3

Supportive Care Measures

Essential supportive interventions include:

• Oxygen therapy to maintain pO2 >8 kPa or SaO2 >92% 1, 2
• Adequate hydration (assess need for IV fluids) 1, 2
• Antipyretics for fever management 2
• Nutritional support in severe or prolonged illness 2

Critical Pitfalls to Avoid

Do NOT use corticosteroids for influenza treatment unless clinically indicated for another reason (asthma/COPD exacerbation, septic shock), as they increase mortality risk and bacterial superinfection rates. 1, 2, 7, 5

Do NOT use amantadine or rimantadine for influenza B, as these agents have no activity against influenza B virus. 1, 7

Monitoring and Reassessment

Monitor vital signs at least twice daily: temperature, respiratory rate, pulse, blood pressure, mental status, and oxygen saturation. 2

Reassess the patient if:

• No clinical improvement within 48 hours of starting antivirals 2
• Fever persists beyond 4-5 days 2
• Clinical deterioration occurs 2, 3
• No improvement after 3-5 days of antiviral treatment 2, 3

In these scenarios, investigate alternative diagnoses and bacterial coinfection. 1, 3

Hospital Admission Criteria

Admit high-risk patients with influenza who have:

• Pneumonia with CURB-65 score ≥2 1
• Bilateral chest X-ray changes suggesting primary viral pneumonia 1
• Worsening illness despite outpatient management 1
• Oxygen requirement 1
• Inability to maintain oral hydration 1