Reports of Severe Influenza Signal the Start of Flu Season, CDC Says

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An increase in influenza activity across the nation has prompted the Centers for Disease Control and Prevention (CDC) to issue a Feb. 1 health advisory regarding the start of this year’s flu season. The Pennsylvania Department of Health (DOH) has forwarded the CDC’s advisory to alert the state’s health care providers.

The CDC urges rapid antiviral treatment without waiting for testing when treating patients who are very ill or at high risk. While early antiviral treatment works best to reduce morbidity and mortality, treatment may offer benefit when started up to four to five days after symptom onset in hospitalized patients.

Co-circulation of influenza A(H3N2), A(H1N1)pdm09, and influenza B viruses has been identified since Oct. 2015. However, H1N1pdm09 viruses have predominated recently.

The CDC has received reports of severe respiratory illness in young to middle-aged adults with H1N1pdm09 virus infection. Some cases have required intensive care unit hospitalization, and there have been reported fatalities. Further, the CDC notes that:

  • Some of the cases reported initially tested negative for influenza. As a result, the CDC is recommending antiviral treatment for severely ill and high-risk patients if influenza is suspected or confirmed.
  • Most of the patients were reportedly unvaccinated. Clinicians should continue vaccination efforts as long as viruses as still circulating.

As of Feb. 1, 2016, the 2015-2016 flu season has ranged from mild to severe and is consistent with that of other flu seasons. The CDC reports that national influenza activity is low compared to this time last year, but cautions that activity is increasing.

Currently, flu severity is not elevated, but the CDC will continue to monitor for any indications of increased severity. Get an online map with a weekly state-by-state influenza summary.

The DOH adds that flu activity in Pennsylvania remains relatively low overall at the present time. Although circulation of the H1N1pdm09 strain is increasing in Pennsylvania as it is in the rest of the country, as yet there have been no reports in PA of severely ill young to middle-aged adults infected with H1N1pdm09.

Lab data does indicate that most circulating flu viruses are still like the viruses recommended for the 2015-2016 influenza vaccines. The H1N1pdm09 strain is included in this year’s flu vaccine and is a good match. It’s important to encourage patients who have not yet been vaccinated to get the influenza vaccination.

The CDC will monitor vaccine effectiveness and publish weekly results here.

Clinical recommendations

The advisory includes these nine recommendations for clinicians:

  1. Clinicians should encourage all patients 6 months of age and older who have not yet received an influenza vaccine this season to be vaccinated against influenza—View CDC vaccine options.
  2. Clinicians should encourage all persons with influenza-like illness who are at high risk for influenza complications to seek care promptly to determine if treatment with influenza antiviral medications is warranted.
  3. Decisions about starting antiviral treatment should not wait for laboratory confirmation of influenza, as rapid antigen detection tests (RIDTs) using immunoassays or immunofluorescence assays have a high potential for false negative results. Antiviral treatment should not be withheld from patients with suspected influenza, even if they test negative by RIDT; initiation of empiric antiviral therapy, if warranted, should not be delayed.
  4. Review CDC guidelines for influenza antiviral use.
  5. When indicated, antiviral treatment should be started as soon as possible after illness onset, ideally within 48 hours of symptom onset as this is when clinical benefit is greatest. However, antiviral treatment might still be beneficial in patients with severe, complicated, or progressive illness, and in hospitalized patients and in some outpatients when started after 48 hours of illness onset, as indicated by clinical and observational studies.
  6. Treatment with an appropriate neuraminidase inhibitor antiviral drugs (oral oseltamivir, inhaled zanamivir, or intravenous peramivir) is recommended as early as possible for any patient with confirmed or suspected influenza who is hospitalized; has severe, complicated, or progressive illness; or is at higher risk for influenza complications—View the advisory for a list of high risk patients.
  7. Antiviral treatment can also be considered for suspected or confirmed influenza in previously healthy, symptomatic outpatients not at high risk on the basis of clinical judgment, especially if treatment can be initiated within 48 hours of illness onset.
  8. Clinical judgment, on the basis of the patient’s disease severity and progression, age, underlying medical conditions, likelihood of influenza, and time since onset of symptoms, is important when making antiviral treatment decisions for outpatients.
  9. While influenza vaccination is the best way to prevent influenza, a history of influenza vaccination does not rule out influenza virus infection in an ill patient with clinical signs and symptoms compatible with influenza. Vaccination status should not impede the initiation of prompt antiviral treatment.