ICD-9 codes

  • 487.0 influenza with pneumonia
  • 487.1 influenza with other respiratory manifestations
  • 487.8 influenza with other manifestations
  • 488.0 influenza due to identified avian influenza virus
  • 488.1 influenza due to identified pandemic (H1N1) 2009

Risk factors for complications

  • Age <5 years or >65 years
  • Pregnancy
  • Chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, cognitive, neurologic/neuromuscular, hematologic, or metabolic disorders (including diabetes mellitus)
  • Immunosuppression, including medication-induced or due to HIV infection
  • Residents of nursing homes and other long-term care facilities
  • Persons <19 years old on long-term aspirin

Diagnosis

  • Diagnosis made clinically with confirmatory testing in selected cases
  • Clinical diagnosis:
    • If influenza already documented in community or geographic area, clinical diagnosis can be made based on signs and symptoms.
    • Signs and symptoms of influenza can vary by age and underlying medical conditions.
    • Not all patients with influenza virus infection will have typical symptoms and signs.
  • Diagnostic testing should be considered if:
    • No recent cases of influenza locally
    • Results would change management, such as deciding whether to use influenza antiviral agents
    • Institutional outbreak of influenza suspected (to allow prompt implementation of control measures)
  • Rapid antigen detection tests:
    • Nasopharyngeal and nasal specimens have higher yields than throat swab specimens for rapid detection.
    • Rapid antigen detection tests have moderate sensitivity and high specificity for influenza.
    • Positive predictive value of rapid influenza tests varies with influenza prevalence.
  • Chest x-ray if signs or symptoms of pneumonia

Antiviral treatment

  • Antivirals include neuraminidase inhibitors (oseltamivir [Tamiflu], zanamivir [Relenza]), and adamantanes (amantadine [Symmetrel], rimantadine [Flumadine])
  • May be indicated if influenza and symptom duration <48 hours
  • Priority groups for treatment
    • Hospital patients (even if >48 hours after symptom onset)
    • Patients at higher risk for influenza complications
    • Patients with lower respiratory tract symptoms
  • Treatment should not wait for laboratory confirmation.
  • For patients not hospitalized or in high-risk group, antivirals are generally not needed.
  • Drug selection may vary based on antiviral resistance patterns.
    • Pandemic (H1N1) 2009 mostly resistant to adamantanes, sensitive to neuraminidase inhibitors
    • Seasonal influenza A (H1N1) mostly resistant to oseltamivir and mostly sensitive to zanamivir and adamantanes
    • Seasonal influenza A (H3N2) and influenza B resistant to adamantanes, sensitive to neuraminidase inhibitors
  • Specific drug recommendations may vary with local influenza activity; if co-circulating influenza A subtypes or viruses with varied antiviral susceptibilities, use zanamivir, or oseltamivir plus adamantane.
  • Dosing in adults (treatment duration five days)
    • Oseltamivir 75 mg orally twice daily
    • Zanamivir 10 mg (two inhalations) twice daily; not recommended in patients with airways disease
    • Amantadine 200 mg orally once daily or 100 mg twice daily
    • Rimantadine 100 mg orally twice daily
    • Dose may be reduced if renal impairment (for oseltamivir or adamantanes), age >65 years (for adamantanes) or adverse effects (for adamantanes).
  • Efficacy of neuraminidase inhibitors in otherwise healthy adults with influenza (but results may vary with antiviral resistance patterns)
    • Modest reduction in duration of influenza (by one-half to one day)
    • Reduction in rates of secondary complications
    • Possible reduction in antibiotic use and hospitalizations
  • Antiviral agents may be associated with reduced mortality in adults hospitalized for influenza.
  • Neuraminidase inhibitors have been associated with neuropsychiatric symptoms, including self-injury and delirium.
  • Also consider antiviral prophylaxis for high-risk close contacts.
  • Dosing similar to treatment except once daily dosing for neuraminidase inhibitors.
  • Postexposure chemoprophylaxis recommended for high-risk persons with close contact during infectious period (one day before symptoms until 24 hours after fever ends)

Other treatment considerations

  • Antipyretics may reduce fever and discomfort but insufficient evidence on effect on duration of influenza.
  • Alternative treatments have insufficient evidence, but elderberry extract (Sambucol) may reduce influenza symptoms.
  • Avoid work or school for at least 24 hours after last fever.

For complete references, see www.ebscohost.com/dynamed/.