It's the time of year when seasonal influenza rates typically start to pick up, and the CDC has begun receiving reports of severe illness caused by a particular strain of flu virus that is circulating this year. As a result, the agency is calling on physicians(emergency.cdc.gov) to be more proactive in prescribing antiviral medications for seriously ill or high-risk patients in whom flu is suspected or confirmed.
Influenza A(H3N2), A(H1N1)pdm09, and influenza B viruses have all been circulating since October, said agency officials in a Feb. 1 CDC Health Advisory. In recent weeks, however, H1N1pdm09 viruses have predominated, and the CDC has received recent reports of severe respiratory illness among young- to middle-aged adults infected by this particular strain. Some of these patients have required ICU admission, and fatalities have been reported. Most were unvaccinated.
In the past, H1N1pdm09 virus infection has been known to cause severe illness in children and young- and middle-aged adults, and the agency urges clinicians to continue vaccinating patients for as long as influenza viruses are circulating this season.
The situation is particularly concerning because in a number patients who have become seriously ill, rapid influenza diagnostic test (RIDT) results were negative; the diagnosis was confirmed only later via molecular assays. This has prompted CDC officials to issue a number of recommendations, including the following:
- Encourage all patients who have not yet received the annual influenza vaccine this season to be vaccinated. This recommendation applies to patients age 6 months and older in whom no contraindications to vaccination exist.
- Encourage anyone with flu-like illness who is at high risk for influenza complications (e.g., patients younger than age 2 years or older than 65, immunosuppressed individuals, people with certain chronic conditions, etc.) to seek care promptly to determine whether antiviral treatment is warranted.
- Decisions about starting antiviral therapy should not wait for confirmatory lab testing in patients in whom influenza is suspected, even in the presence of a negative rapid antigen detection test (RIDT) result. Given the high incidence of false-negative RIDT results, empiric antiviral treatment, if indicated, should not be delayed.
- If empiric antiviral treatment is indicated, it should be started as soon as possible, preferably within 48 hours of symptom onset. Although clinical benefit is greatest when therapy is started early, some evidence shows that antiviral treatment might still be beneficial in patients with severe, complicated or progressive illness, in hospitalized patients, and in some outpatients even after that 48-hour threshold.
- Treatment with an appropriate neuraminidase inhibitor antiviral drug (oral oseltamivir [Tamiflu], inhaled zanamivir [Relenza] or intravenous peramivir [Rapivab]) should be started as early as possible in any patient with confirmed or suspected influenza who is hospitalized; has severe, complicated or progressive illness; or is at high risk for complications.
The agency also noted that although annual vaccination is the best way to prevent the flu, a history of vaccination does not rule out influenza in a patient with signs and symptoms compatible with the illness. Thus, a patients' vaccination status should not preclude initiation of antiviral treatment in the presence of suspicious clinical features.
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