New IDSA Influenza Guidelines

January 29, 2019

Written by Clay Smith

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This is the IDSA influenza guideline, updated from 2009.  It covers testing, treatment, complications, and more. This is long, but it’s less than the guideline’s 47 pages.

Why does this matter?
Most cases of influenza are self limited.  However, each year, thousands of patients die from it, especially those with chronic heart and lung problems, immunocompromised patients, and pregnant/postpartum women.

It’s the most wonderful time of the year!

This IDSA clinical practice guideline helps us think through the flu by answering several key questions.

Who needs influenza testing?

Outpatient
During times of high influenza activity, test in high risk patients if it will change management.  Otherwise, if symptoms are consistent with influenza and the patient warrants treatment, empiric therapy can be initiated. During times of low influenza prevalence, testing may be considered in high risk or immunocompromised patients with respiratory symptoms, but false positive rapid antigen tests are common.

Inpatient
Hospitalized patients with respiratory illness, especially those with chronic heart and lung disease or immunocompromise during times of high flu prevalence, should be tested.  In times of low prevalence, test only if there is an epidemiological link to someone with influenza.

What specimen should be used?
Deep, mid-turbinate nasopharyngeal swabs, as early as possible in the illness, are preferred.  In the hospital, endotracheal aspirates or BAL are options.

What influenza test should be used?
Nucleic acid amplification tests (NAATs) are preferred over rapid influenza diagnostic tests (RIDTs) in outpatients.  Sensitivity for RIDTs ranges from the 60s-80s%, whereas the NAATs have mid to high 90% sensitivity and near 100% specificity.  NAATs were impractical in many settings, such as small retail clinics, but now at least one available test is CLIA waived and can be run in under 15 minutes.  NAATs or RT-PCR should be used in patients who are hospitalized or likely to be hospitalized.

Which patients should be treated for influenza?
Usually, treatment of patients without high risk of influenza complications is recommended within 2 days and should be with a neuraminidase inhibitor (NAI) like oseltamivir, inhaled zanamivir, or (not mentioned in this guideline) baloxivir.  The benefit in such patients is small and may reduce the duration of the illness by a half day or so.  They also mention benefit to treating symptomatic patients who are household contacts with people at high risk of flu complications, especially those with severe immunocompromise, and healthcare workers who contact patients at high risk.  Treatment of low risk patients is fraught with conflict of interest and low quality evidence.  See EM Lit of Note for more discussion.

This guideline emphasizes that there are several groups who benefit from NAI even if outside the 48h window, again with fairly low quality evidence:

• All hospitalized patients

• Outpatients with progressive or severe disease

• Outpatients at high risk of complications from influenza, i.e. chronic medical conditions or immunocompromised patients

• Children <2 years and adults ≥65 years

• Pregnant  women and those within 2 weeks postpartum

What drug, dose, and duration?
The four main drugs are oseltamivir, zanamivir, baloxivir (not mentioned in this IDSA iteration), and IV peramivir.  Doses should be per FDA recommendations for each – look it up.  Treatment with the first two is 5 days.  The others are one-time doses.

When should bacterial co-infection be considered?

• Severe disease – pneumonia, hypotension, etc.

• Deterioration after initial improvement

• Failure to improve in 3-5 days.

Should adjunctive medications be added?
Avoid steroids if at all possible unless there is a compelling indication (severe asthma exacerbation) and don’t give IVIG.

When should antiviral chemoprophylaxis be used?

• In patients >3 months old at high risk of flu complications

• It may also be used in outbreaks or to prevent outbreaks, especially in institutionalized patients.

• The guideline goes on to discuss more on chemoprophylaxis and institutional outbreaks, which is outside the scope of the ED.

Source
Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenza.  Clin Infect Dis. 2018 Dec 19. doi: 10.1093/cid/ciy866. [Epub ahead of print]

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Reviewed by Thomas Davis