Rates of influenza reported in the United States are increasing, according to the Centers for Disease Control and Prevention (CDC), with influenza A (H1N1)pdm09 viruses predominating.

In addition, federal health officials are noting reports of severe illness caused by the influenza prompting a health alert for health care practitioners:

generic influenza virion
3D influenza/CDC

Clinicians are reminded to treat suspected influenza in high-risk outpatients, those with progressive disease, and all hospitalized patients with antiviral medications as soon as possible, regardless of negative rapid influenza diagnostic test (RIDT) results and without waiting for RT-PCR testing results. Early antiviral treatment works best, but treatment may offer benefit when started up to 4-5 days after symptom onset in hospitalized patients. Early antiviral treatment can reduce influenza morbidity and mortality.

CDC has received recent reports of severe respiratory illness among young- to middle-aged adults with H1N1pdm09 virus infection, some of whom required intensive care unit (ICU) admission; fatalities have been reported.

Some of these patients reportedly tested negative for influenza by RIDT; their influenza diagnosis was made later with molecular assays. Most of these patients were reportedly unvaccinated. H1N1pdm09 virus infection in the past has caused severe illness in some children and young- and middle-aged adults.

Clinicians should continue efforts to vaccinate patients this season for as long as influenza viruses are circulating, and promptly start antiviral treatment of severely ill and high-risk patients if influenza is suspected or confirmed.

Providers should encourage all patients who have not yet received an influenza vaccine this season to be vaccinated against influenza. This recommendation is for patients 6 months of age and older.

When indicated, antiviral treatment should be started as soon as possible after illness onset, ideally within 48 hours of symptom onset.

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