This is an official CDC HEALTH ADVISORY
Distributed via Health Alert Network
Friday, February 29, 2008, 14:10 EST (02:10 PM EST)
CDCHAN-00271-2008-02-29-ADV-N
Influenza Antiviral Use for Persons at High Risk for
Influenza Complications or Who Have Severe Influenza Illness
CDC is alerting clinicians to be fully aware of the potential
benefits of influenza antiviral medications during this influenza season.
Summary:
Recent
surveillance data indicate that many communities are reporting substantially
increased influenza activity. This CDC Health Advisory is intended to
re-emphasize the importance of considering antiviral medications
for use in the treatment or prevention of influenza. The two
prescription antiviral medications recommended for treatment or prevention of
influenza include oseltamivir (Tamiflu®, Roche Laboratories, Nutley, NJ) or
zanamivir (Relenza®, GlaxoSmithKline, Research Triangle Park, NC). These
antiviral medications are also known as neuraminidase inhibitors. Recent
studies suggest a considerable protective effect against complications
associated with influenza when neuraminidase inhibitors are used for treatment.
These benefits include reducing the risk of death among older adults
hospitalized with laboratory-confirmed influenza. Because high levels of
resistance to adamantane antiviral medications (rimantadine and amantadine)
continue to be observed among circulating influenza A viruses, adamantanes are
not recommended for treatment or prevention of influenza.
Background:
During this influenza season, a
small increase in the number of influenza viruses resistant to oseltamivir has
been observed in the United States. Among the 471 influenza A and B viruses
tested during the 2007–08 influenza season to date, 27 (5.7%) have been found
to be resistant to oseltamivir, compared with 0.7% during the 2006-07 season.
All of the oseltamivir-resistant viruses have been influenza A viruses of the
H1N1 subtype; 8.7% of the 310 H1N1 viruses tested are resistant to oseltamivir.
No resistance to oseltamivir has been observed among the 161 influenza A (H3N2)
and influenza B viruses tested to date, and no antiviral resistance to
zanamivir has been detected in any subtype.
Recommendations:
Given the low level of overall resistance to oseltamivir among circulating
influenza viruses, the finding of resistance only in influenza A (H1N1)
viruses, and no resistance to zanamivir, neuraminidase inhibitor medications
continue to be recommended for the treatment and chemoprophylaxis of influenza.
Antiviral treatment should begin within 48 hours of symptom onset if possible,
but treatment should still be considered for persons who present more than 48
hours after illness onset if they have severe influenza illness or are at
higher risk for severe complications from influenza. Oseltamivir is approved
for treatment and prevention of influenza for persons 1 year and older, while
zanamivir is approved for treatment of persons 7 years and older and prevention
of influenza in persons 5 years and older. Enhanced surveillance for
detection of oseltamivir-resistant influenza viruses is ongoing, and antiviral
usage recommendations will be revised to account for changes in antiviral
resistance trends as needed. Influenza A viral isolates from affected persons
in institutional outbreaks should be subtyped. Health care providers should
contact their local or state public health department for assistance when an
outbreak of influenza in an institutional setting (e.g., a long-term care
facility) occurs. State health departments should consult with CDC about the
need for antiviral resistance testing when influenza A (H1N1) viral isolates are
obtained from outbreaks in institutional settings.
In some
communities, circulating influenza virus strains during this influenza season
are antigenically different from those contained in current influenza
vaccines. Preliminary results from a rapid assessment of vaccine
effectiveness suggest that currently available influenza vaccines provide some
protection against influenza virus infection requiring medical care. However,
the level of protection is likely to be lower than what is observed in seasons
in which the vaccine strains are closely matched to circulating influenza virus
strains. When influenza vaccine effectiveness is reduced, clinicians should be
aware of the potential for appropriately vaccinated persons to develop
influenza despite vaccination.
Because approximately 2 weeks is
required to develop an optimal immune response to influenza vaccination, use of
neuraminidase inhibitors for prevention of influenza during a confirmed
influenza institutional outbreak should be considered for persons at higher
risk for influenza complications and who were vaccinated within the previous 2
weeks. Persons who were vaccinated more than two weeks before a suspected
influenza virus exposure, but who are less likely to develop protective
immunity after vaccination (e.g., persons in long-term care facilities or
persons with immunosuppression), can be considered for antiviral
chemoprophylaxis when local influenza surveillance data indicate that influenza
activity is high.
Clinicians should consider
whether to recommend influenza antiviral treatment based on the severity of the
patient’s illness, the time since illness onset, local influenza surveillance
data and influenza test results. Rapid diagnostic tests for influenza have good
specificity, but are only moderately sensitive. Positive rapid tests are
generally reliable when influenza activity is high in a community and are
useful in deciding whether to initiate antiviral treatment. Negative rapid test
results are less helpful in making treatment decisions. When local influenza
activity is high, persons with severe respiratory symptoms or persons with
acute respiratory illness who are at higher risk for influenza complications
should still be considered for influenza antiviral treatment despite a negative
rapid influenza test unless illness can be attributed to another cause. As
reported in a previous HAN, persons with severe influenza illness should also
be assessed for invasive bacterial co-infection, and appropriate antimicrobial
therapy directed at potential bacterial pathogens, such as
methicillin-resistant Staphylococcus aureus, might be necessary.
To reduce the substantial burden
of influenza in the U.S., CDC continues to recommend a three-pronged
approach: influenza vaccination, use of neuraminidase inhibitor antiviral
medications when indicated for treatment or prevention, and use of other
measures to decrease the spread of influenza, including promotion of hand
hygiene, respiratory hygiene, cough etiquette, and staying home from work and
school when ill. Clinicians in communities experiencing increased influenza
activity should consider prescribing the neuraminidase inhibitor antiviral
medications oseltamivir and zanamivir for the treatment of influenza patients
or for prevention of influenza when indicated for institutional influenza
outbreaks or for persons at high risk for complications from influenza who have
contraindications to influenza vaccination.
For more information, please
see the CDC website: http://www.cdc.gov/flu/professionals/antivirals/
If you have any questions about
this Health Advisory, please call the Influenza Division, Epidemiology and
Prevention Branch at 404-639-3747.
After normal business hours,
contact CDC’s duty officer through the CDC Director’s Emergency Operation
Center (DEOC) at (770) 488-7100.
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