Influenza and Influenza Pneumonia

Acute Bronchitis

Influenza and Influenza Pneumonia

Definition/Key Clinical Features
Differential Diagnosis
Best Tests
Best Therapy
Best References

Definition/Key Clinical Features

• Abrupt onset of fever, chills, headache, myalgia, malaise, anorexia, sore throat, cough, rhinorrhea
• Respiratory symptoms more apparent as systemic symptoms subside
  • Protracted cough from viral tracheobronchitis
  • Airway hyperactivity and abnormal pulmonary function test results for weeks to months
  • Severe exacerbation of chronic pulmonary disease (asthma, bronchitis)

• Rapidly progressive dyspnea, severe cough, cyanosis, diffuse rales, wheezing, variable sputum production, sometimes bloody
• Ranges from mild to rapidly fatal
• 1–7 days after typical influenza onset
• High mortality

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Differential Diagnosis

• Other acute viral and bacterial respiratory diseases

• Secondary bacterial pneumonia

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Best Tests

• Rapid assays for influenza A and B
  • Specificity good
  • Sensitivity 50%–90%, depending on age, specimen type, and illness duration
  • Sensitivity 50%–60% in adults
• Sputum Gram stain may show polymorphonuclear neutrophils but rarely bacteria in primary viral pneumonia
• Chest x-ray: bilateral (diffuse interstitial) infiltrates
• Perihilar pulmonary edema or dense opacification
• CBC: variable WBC count (leukopenia and lymphopenia to leukocytosis with left shift); thrombocytopenia

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Best Therapy

Antiviral Drugs

• Neuraminidase inhibitors
  • Active against both A and B
  • Effective for early treatment; reduce symptoms and functional disability by 1–3 days
  • Reduce risk of lower respiratory tract complications; oseltamivir also reduces risk of otitis in children and hospitalization in adults
  • Oseltamivir
    • Dosage: adults and teenagers, 75 mg b.i.d. for 5 days; children ≥ 1 year, 30–75 mg (based on body weight) b.i.d. for 5 days
  • Zanamivir
    • Dosage: in adults and children ≥ 7 years, two puffs b.i.d. for 5 days
    • Two doses should be taken on the first day of treatment, provided that at least 2 hr elapse between doses
• M2 inhibitors
  • Activity against influenza A viruses only
  • Increasing antiviral resistance in circulating influenza strains makes these agents unreliable in absence of susceptibility data
  • Currently not recommended for the routine management of influenza
  • Consult current CDC recommendations before using these agents: http://www.cdc.gov/flu/professionals/treatment
  • For susceptible influenza A strains
    • Effective for early treatment: reduce fever and symptoms by 1–2 days
  • Amantadine
    • Dose: 100 mg b.i.d.; reduce dose for age ≥ 65 years or renal insufficiency (creatinine clearance < 50–80 ml/min)
  • Rimantadine
    • Dose: 100 mg b.i.d. or 200 mg q.d.; reduce dose for severe hepatic dysfunction, age ≥ 65 years, or renal insufficiency (creatinine clearance < 10 ml/min)

• Treatment primarily supportive
  • Oxygen; ventilatory support sometimes needed
  • Antivirals often used
  • Screen for bacterial superinfection

Antiviral Drugs

• Neuraminidase inhibitors
  • Effective for influenza A and B prophylaxis
  • Effective as seasonal prophylaxis or for prophylaxis after an exposure
  • For postexposure prophylaxis, start within 48 hr after exposure to influenza
  • Oseltamivir
    • Dosage: adults and teenagers, 75 mg daily for 7–10 days; children ≥ 1 year, 30–75 mg (based on body weight) daily for 7–10 days
  • Zanamivir
    • Dosage: adults and children 5 years and older, two puffs once daily for 7–10 days
• M2 inhibitors
  • Amantadine and rimantadine
  • Previously 70%–90% effective against influenza A strains
  • Increasing resistance has made these agents unreliable
  • Currently not recommended for prophylaxis
  • Consult current CDC advice before using these agents: http://www.cdc.gov/flu/professionals/treatment

• IM and intranasal forms
  • Both trivalent (2 A, 1 B); both use egg-grown virus, possible reactions in allergic patients
  • Take several weeks to elicit immunity
  • Efficacy of IM vaccine 70%–90% in young and middle-aged adults, lower in elderly; approved for patients 6 months and older, including high-risk groups
  • Intranasal vaccine approved for previously healthy patients 5 to 49 years
  • Intranasal vaccine is live-attenuated and therefore contraindicated in patients with known or suspected immune deficiencies

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Best References

Kaiser L, et al: Curr Clin Top Infect Dis 19:112, 1999 [PMID 10472483]

Moscona A: N Engl J Med 353:1363, 2005 [PMID 16192481]

Pearson ML, et al: MMWR Recomm Rep 55:1, 2006 [PMID 16498385]

Writing Committee of the World Health Organization Consultation on Human Influenza A/H5: N Engl J Med 353:1374, 2005 [PMID 16192482]

November 2006

Acute Bronchitis

Definition/Key Clinical Features
Differential Diagnosis
Best Tests
Best Therapy
Best References

Definition/Key Clinical Features

• Troubling or prolonged (less than 3 wk) cough
• Nonproductive cough or cough with scant mucoid sputum
• Variable wheezing
• Acute or subacute onset usually following viral upper respiratory illness
• No fever, dyspnea, or chest pain

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Differential Diagnosis

• Pneumonia
• Infection
  • Bacterial
  • Mycoplasmal
  • Chlamydial
  • Pertussis
• For prolonged cough, consider the following
  • Asthma
  • Reflux
  • Postnasal drainage

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Best Tests

• History and physical exam are usually sufficient for diagnosis
• Chest x-ray is normal or unchanged
  • Best test to rule out pneumonia

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Best Therapy

• Antibiotics generally not indicated
• Oseltamivir treatment of acute influenza reduces frequency of acute bronchitis
• Cough suppressant with codeine or dextromethorphan may be helpful in protracted cough (use with caution in patients with underlying chronic obstructive disease)
• Inhaled beta agonist bronchodilators (e.g., albuterol) may decrease duration of cough

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Best References

Gonzales, et al: Ann Intern Med 133:981, 2000

Kaiser, et al: Arch Intern Med 163:1667, 2003

Smucny, et al: Cochrane Database Syst Rev (4):CD000249, 2003

July 2004

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