The updated guideline from the Infectious Diseases Society of America (IDSA) addresses some new information on influenza regarding diagnostic testing, treatment, and chemoprophylaxis with antiviral medications.

The guideline has put special consideration for patients such as children, older adults, pregnant and postpartum women and immunocompromised patients, who are at high risk for complications from influenza.

Seasonal influenza is associated with significant morbidity and mortality worldwide. Uncomplicated influenza is easily curable, however, in some cases, influenza can cause complications that result in severe illness and death.

Use of appropriate diagnostic tools and accurate interpretation of results can help in early identification of influenza cases. Prompt diagnosis also helps to decrease the unnecessary laboratory testing for other etiologies and the use of antibiotics. Effective treatment with an appropriate antiviral agent can lower the duration of symptoms and risk of development of complications. It also reduces the rate of hospitalization, and decreases the overall mortality among high-risk populations.

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Key takeaways from the updated IDSA guideline

Patients who need to be tested for iInfluenza

A. Outpatients with suspected influenza activity

• High-risk patients, who present with influenza-like illness, pneumonia, or nonspecific respiratory illness
• Patients who present with acute onset of respiratory symptoms with or without fever, and either exacerbation of chronic medical conditions or known complications of influenza
• Patients not at high risk for influenza complications who present with influenza-like illness, pneumonia, or nonspecific respiratory illness

B. Outpatients with low influenza activity (and no link to an influenza outbreak)

• Patients with acute onset of respiratory symptoms with or without fever, especially for immunocompromised and high-risk patients

C. Hospitalized Patients with influenza activity

• Clinicians should test patients requiring hospitalization with acute respiratory illness; those with acute worsening of chronic cardiopulmonary disease
• Immunocompromised patients or those at high risk of complications presenting with acute onset of respiratory symptoms

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Recommendations for tests to be used to diagnose influenza

1. The use of rapid molecular assay in outpatients, and reverse-transcription polymerase chain reaction in hospitalized patients, is recommended to improve detection of influenza virus.
2. In immunocompromised patients who are hospitalized, multiplex RT-PCR assays targeting a panel of respiratory pathogens (including influenza virus), should be used.
3. The use immunofluorescence assays in hospitalized patients for antigen detection is not recommended. In case it is used, a follow-up testing with RT-PCR should be done to confirm false negatives.
4. The use of viral culture for initial or primary diagnosis is discouraged due to the increased amount of time required for results. It can, however, be an option to confirm false negatives from rapid-influenza diagnostic tests and immunofluorescence assays, especially during an institutional outbreak.
5. The use of serologic testing is not recommended due to problems in interpretation and the requirement of paired (acute/convalescent) sera.

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Recommendations on treatment

Appropriate antiviral treatment should be promptly initiated in patients with suspected influenza (irrespective of vaccination). Treatment should be started in the following:

• Hospitalized patients as well as outpatients (with severe illness)
• Outpatients at high risk; with chronic medical conditions and immunocompromised patients
• Children younger than 2 years and adults ≥65 years
• Pregnant women as well as those within 2 weeks postpartum
• Treatment is also recommended for those at a lower risk, in following circumstances:
• Outpatients with illness onset less than or equal to 2 days
• Symptomatic persons and healthcare providers who are in immediate contact with the high risk group

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Selecting the Antiviral Drug of Choice

1. The guideline recommends treatment to be initiated with a single neuraminidase inhibitor (NAI) rather than a combination of NAIs. Oral oseltamivir, inhaled zanamivir, or intravenous peramivir are the drug of choice. Frequent use of higher doses of NAI drugs is however discouraged.
2. Uncomplicated cases, in otherwise healthy outpatients, should be treated for 5 days; longer duration of treatment may be considered in immunocompromised individuals or patients requiring hospitalization.
3. In addition to antiviral treatment, treatment for bacterial coinfection may be considered in following patients:
4. Patients with suspected or laboratory-confirmed influenza with severe disease
5. Patients who deteriorate after initial improvement, particularly in those treated with antivirals
6. Patients who fail to improve after 3–5 days of antiviral treatment
7. Causes other than influenza virus should be considered in those who fail to improve or deteriorate despite antiviral treatment.

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Detecting infection with an antiviral-resistant influenza virus

Influenza NAI resistance testing is recommended in patients who develop laboratory-confirmed influenza while on or immediately after NAI chemoprophylaxis and those who remain ill during or after NAI treatment. Resistance testing is also encouraged in immunocompromised patients and in cases with persistent influenza viral replication.

Other conditions which warrants resistance testing:

• Patients (with laboratory-confirmed influenza) who have received sub-therapeutic NAI dosing
• Severe cases with no improvement with NAI treatment and have evidence of persistent influenza viral replication

Clinicians should not use corticosteroid adjunctive therapy in suspected or confirmed Influenza cases unless clinically indicated for other reasons. The frequent use of immunomodulation is also not recommended.

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Antiviral chemoprophylaxis

The authors suggest that antiviral chemoprophylaxis should not be a substitute for influenza vaccination. The decision to use antiviral chemoprophylaxis must be taken after considering the risk of emergence of resistance, risk of severe complications of influenza, the potential for side effects, and the ability to initiate early therapy for influenza.

Patient education and early empiric antiviral therapy, in case influenza symptoms develop, are suitable alternatives to post-exposure antiviral chemoprophylaxis, however more evidence, in the form of clinical studies, for the same are warranted.

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Institutional outbreak management of seasonal influenza

On identification of an influenza case in an institution such as hospital or long-term care facility, active surveillance for additional cases and effective measures to control the outbreak should be implemented.

Antiviral chemoprophylaxis of residents/ patients is recommended as soon as possible; even in circumstances when results of molecular testing are pending.