Influenza

Influenza: Excerpt from The 5-Minute Pediatric Consult

Kristen A. Feemster, MD, MPHJoel A. Fein, MD, MPH

Influenza - BASICS

Influenza - description

An acute febrile illness characterized by fever and respiratory and gastrointestinal symptoms

Influenza - general prevention

• Vaccination:
  • American Academy of Pediatrics recommendations for influenza vaccination:
    • Children who are between 6 and 59 months old during influenza season (October through March); children and adolescents who are at high risk for complications from influenza infection (see “Physical Exam”)
    • Health care professionals and caregivers who have frequent contact with children 0–59 months old or any high-risk persons
  • Vaccine types:
    • Trivalent inactivated influenza vaccine (TIV) approved for children >6 months. Live-attenuated influenza vaccine (LAIV), licensed as FluMist in the US; administered as an intranasal spray; approved only for healthy 5–49 year olds; not recommended for “high-risk” persons or their contacts. Children receiving chronic aspirin therapy should not be considered for vaccination with LAIV because of the associations among aspirin use, influenza infection, and Reye syndrome.
  • Children <10 years old receiving influenza vaccination for the 1st time should receive 2 doses of vaccine administered at least 1 month apart.
  • People with a known anaphylactic hypersensitivity to eggs should consult a physician before receiving the vaccine.
• Chemoprophylaxis:
  • Prophylactic administration of antiviral medications is indicated for: High-risk children who are vaccinated after influenza activity has begun within 2 weeks after the final dose of vaccine was given, immunocompromised patients who have a poor response to vaccine, and high-risk patients who cannot receive the vaccine (anaphylactic reaction to chicken or eggs); also for control of outbreaks in institutions housing high-risk people
  • The neuraminidase inhibitors zanamivir and oseltamivir are now approved for prophylaxis. Amantadine and rimantadine should not be used due to widespread resistance.

Influenza - epidemiology

• Although influenza affects people of all ages, the highest morbidity and mortality occur in infants and the geriatric population.
• The attack rate is highest among school-aged children and ranges from 10–40%. 1% of infections result in hospitalization.
• Epidemics of influenza occur almost exclusively during winter months, peak ~2 weeks after the index case, and last 4–8 weeks. Up to 75% of school children in the epidemic region may be affected.
• Transmission of influenza virus occurs by aerosol droplets as well as by direct or indirect contact.
• Complication rates increase in children <2 years old and those with high-risk conditions (see “Complications”).

Influenza - risk factors

High risk conditions for severe disease include: Chronic pulmonary disease (i.e., asthma), hemodynamically significant cardiac disease, HIV and other immunodeficiencies, chronic immunosuppressive therapy, hemoglobinopathies (i.e., sickle cell disease), long-term salicylate use, chronic renal dysfunction, and chronic metabolic disease.

Influenza - etiology

• The orthomyxoviruses influenza types A, B, and C. Influenza C virus has not been reported as a cause of influenza epidemics.
• Influenza A has subtypes defined by 2 surface antigens: Hemagluttinin and neuraminidase.

Influenza - associated conditions

• Pharyngitis
• Laryngotracheitis (croup)
• Bronchitis/bronchiolitis
• Pneumonia
• Gastroenteritis
• Conjunctivitis

Influenza - DIAGNOSIS

Influenza - signs & symptoms

• Infection with influenza virus causes distinct clinical pictures based on the age of the affected individual:
  • Infants and young children may suffer higher fevers and more severe respiratory symptoms.
  • Many older children and adults infected with influenza are diagnosed with a “viral respiratory infection,” without specific reference to the viral etiologic agent.
• The diagnosis of influenza infection is more commonly made in light of previously identified index cases or specific findings, such as myositis.

Influenza - history

• Abrupt onset of illness, beginning with dry cough, coryza
• Fever, headache, anorexia, malaise, myalgias, sore throat, irritability
• Respiratory complaints range from mild cough to severe respiratory distress (infants).
• GI complaints in younger children may include vomiting, diarrhea, and severe abdominal pain.

Influenza - physical exam

• Cough is the predominant respiratory sign. Infants and small children may exhibit a “barky” cough (croup).
• Nasal congestion and conjunctival and pharyngeal infections are common.
• Cervical adenopathy is more common in children than in adults.
• Neonates may appear septic: Apnea, circulatory collapse, petechiae
• A generalized macular or maculopapular rash is sometimes observed.
• Leg weakness/Inability to walk due to myositis (usually in the convalescent phase of influenza infection and limited to or most severe in the gastrocnemius and soleus muscles.

Influenza - tests

Influenza - lab

• Viral culture from nasopharyngeal secretions will be positive within 2–6 days.
• Direct immunofluorescent antibody (DFA) and indirect immunofluorescence antibody (IFA) tests have moderate sensitivity (6–70%) and excellent specificity (>95%), and are completed within 2–4 hours. Predictive value greatly affected by prevalence of circulating influenza.
• Rapid antigen testing is available for diagnosing influenza A and influenza B. The newer tests are moderately sensitive (70–80%) and highly specific (94–97%), and can be completed within 10–15 minutes.
• Serologic evidence of infection involves comparison of acute and convalescent serum antibody titers (at least 10–14 days apart). Enzyme-linked immunosorbent assay for influenza is also available.
• False positives: Culture is the gold standard for diagnosis of influenza.
  • The false-positive rate of DFA, IFA, and rapid antigen testing may be as high as 20% for influenza A and 40% for influenza B.
  • The use of nasopharyngeal aspirates rather than nasopharyngeal swabs may reduce this false-positive rate by 5–10%.

Influenza - imaging

Chest x-ray:

• X-rays of patients with lower airway involvement are indistinguishable from those in patients with other viral lower respiratory infections.
• May be normal despite significant respiratory involvement

• The leukocyte count in patients with influenza may be high, low, or normal.
• The differential count is too variable to be of help in diagnosis.
• Evaluation of oxygenation by arterial blood gas analysis or pulse oximetry may be required in severe cases of influenza infection. Infants without radiologic evidence of lower respiratory tract infection can experience apnea or rapid decrements in pulmonary function.
• A patient with benign acute viral myositis might have an elevated creatine phosphokinase (CPK). However, myoglobinuria might suggest acute viral rhabdomyolysis which can damage the kidneys. These patients should be hospitalized and monitored for adequate hydration.

Influenza - differencial diagnosis

• Viral infections including but not limited to respiratory syncytial virus, parainfluenza, adenovirus
• Streptococcus pyogenes infection
• Bacterial sepsis in young infants

Influenza - TREATMENT

Influenza - initial stabilization

• With the exception of young infants, previously healthy children with influenza infection rarely require emergency treatment.
• Humidified air, with oxygen as needed, is helpful to most patients with respiratory symptoms of influenza.
• Airway maneuvers, including endotracheal intubation, may be required for severe laryngotracheitis or patients with hypoxia that is unresponsive to high-flow oxygen administration.

Influenza - general measures

• Most patients with influenza infection require supportive oral hydration, antipyresis, and routine decongestant therapy.
• Antitussive medications should be used cautiously, and should be appropriate to the age of the child.
• Neuraminidase inhibitors are most effective if used within the 1st 2 days of symptom onset.

Influenza - medication

• Symptom severity and duration may be reduced if antiviral medications are administered within 2 days of symptom onset.
• Antiviral medications have not been proven to reduce serious complications of influenza infection in children, but they may reduce minor complications such as otitis media and shorten the symptom duration by ~1 day.
  • Although Amantadine hydrochloride and Rimantadine are approved for treatment of Influenza A in children >1 year of age, the CDC has recommended against their use for both treatment and prophylaxis due to increasing resistance. Neither are effective against influenza B.
  • The neuraminindase (NA) inhibitors (zanamivir and oseltamivir) are the only antiviral agents active against both influenza A and B.
    • Zanamivir (two 5-mg inhalations b.i.d. daily for 5 days) is approved for treatment in children ≥7 years and prophylaxis in children ≥5 years of age.
    • Oseltamivir (2 mg/kg with maximum 75 mg b.i.d. daily for 5 days) is approved for treatment and prophylaxis in children ≥1 year of age.
• Duration: Therapy should be given until 1–2 days after the disappearance of signs and symptoms. The NA inhibitors should be used for a full 5-day course.
• Important considerations:
  • Inhalation of zanamivir may cause bronchospasm, and should not be prescribed to asthmatics.
  • Oseltamivir may cause nausea or vomiting.

Influenza - FOLLOW UP

When to expect improvement:

• Fever associated with influenza infection usually lasts up to 5 days. Recrudescence of fever does not necessarily signify the onset of a secondary bacterial infection.
• Cough may last up to 2 weeks.
• Lethargy or malaise may persist for up to 2 weeks.
• Influenza A infection usually lasts longer than influenza B or influenza C infection.

Influenza - complications

• Secondary bacterial infections (10% of children):
  • Bacterial pneumonia (pneumococcal or staphylococcal)
  • Otitis media (24%)
  • Sinusitis
• Primary progressive viral pneumonia:
  • Pulmonary hemorrhage
  • High morbidity and mortality rates
• Acute myositis during convalescent period is most commonly associated with influenza B infection:
  • Rhabdomyolysis/myoglobinuria
  • Elevated transaminase levels
• Reye syndrome:
  • Fatty degeneration of the liver and diffuse encephalopathy
  • More commonly associated with influenza B, but may also occur with influenza A
  • Association with aspirin use during acute illness
• Febrile convulsions
• Drug toxicity: Influenza infection may result in increased serum levels of certain medications that are metabolized by the liver.
• Rare sequelae in severe cases of influenza infection:
  • Focal and diffuse myocarditis
  • Diffuse cerebral edema
  • Mediastinal lymph node necrosis
  • Sudden death
  • Guillain-Barré syndrome
  • Encephalitis

Influenza - patient monitoring

Signs to watch for:

• Clinical signs of secondary bacterial infection (see “Complications”)
• Deteriorating mental status or respiratory status after initial improvement
• Myoglobinuria in the face of muscle pain

Influenza - bibliography

American Academy of Pediatrics. Influenza. Red Book: Report of the Committee on Infectious Diseases. Washington, DC: American Academy of Pediatrics; 2006:401–411.
1. American Academy of Pediatrics Committee on Infectious Diseases. Reduction of the influenza burden in children. Pediatrics. 2002;110:1246–1252.
2. Bridges CB, Winquist AG, Fukuda K, et al.; Advisory Committee on Immunization Practices. Prevention and control of influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2000;49(RR-3):1–38.
3. Cooper NJ, Sutton AJ, Abrams KA, et al. Effectiveness of neuraminidase inhibitors in treatment and prevention of influenza A and B: Systematic review and meta-analyses of randomised controlled trials. Brit Med J. 2003;326:1235–1241.
4. Peltola V, Ziegler T, Ruuskanen O. Influenza A and B virus infections in children. Clin Infect Dis. 2003;36:299–305.
5. Smith NM, Bresee JS, Shay DK, et al., Advisory Committee on Immunization Practices. Prevention and control of influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Early Release. 2006;55(ER);1–41.
6. Uyeki TM. Influenza diagnosis and treatment in children: A review of studies on clinically useful tests and antiviral treatment for influenza. Pediatr Infect Dis J. 2003;22:164–177.

Influenza - CODES

Influenza - icd9

487.1 Influenza with other respiratory manifestations

Influenza - FAQ

• Q: When is it safe for a child with influenza to return to day care or school?
• A: Older children with influenza may shed the virus in nasal secretions for up to 7 days from onset of symptoms, and younger children even longer. Therefore, older children with influenza may return to school 1 week after the onset of symptoms, and infants and toddlers should remain home for 10–14 days.
• Q: Can a child on chronic steroid therapy be immunized against influenza?
• A: In general, children who require maintenance steroid therapy for their underlying illness should still receive influenza immunization. If possible, immunize while the child is on the lowest possible dose of steroids and not during a period of high-dose therapy.
• Q: What are the chances of acquiring influenza despite annual vaccination?
• A: Vaccination against influenza is >70–90% effective in preventing disease and >90% effective in preventing death from the infection.
• Q: Is chemoprophylaxis an acceptable alternative for protecting children against influenza?
• A: In general, chemoprophylaxis should not be used as a substitute for vaccination.

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

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More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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