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
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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/.
