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Health advisory: Influenza Activity in King County
March 5, 2009
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ACTION REQUESTED:
- Be aware that influenza activity in King County is increasing
- Be aware of high levels of antiviral drug resistance among influenza A isolates and recent recommendations for treatment with influenza antiviral drugs
- Consider bacterial co-infection with MRSA for patients with influenza-like illness and pneumonia
- Test patients hospitalized with respiratory disease for influenza
- Continue to vaccinate patients throughout the flu season - this remains the most effective way to protect individuals from influenza infection and its complications
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Background: Influenza activity in King County is increasing. Influenza surveillance indicators are lower than seen in recent years at this date; however, it is not possible to predict the severity or peak of seasonal influenza activity. Flu season typically peaks in January or later and has been in February or March in 11 of the past 20 seasons. The numbers of specimens submitted to Public Health's sentinel laboratory-based influenza surveillance system and the proportion positive have been increasing since mid-February. The proportion of rapid antigen tests positive for influenza has increased from 6.6% for the week ending 1/24/09 to 14.7% for the week ending 2/21/09. Emergency department (ED) visits for influenza like illness (ILI) have also increased in the past 4 weeks. Children under 5 years old account for the highest proportion of ED visits for ILI. Influenza A (H1N1) and influenza B isolates are predominant: 70% of isolates have been influenza A and 30% have been influenza B. Of the 19 influenza A isolates that were typed, 18 were influenza A (H1). All influenza A viruses characterized in the U.S. this season are well-matched to the current vaccine; however, the majority of influenza B viruses (including locally) are not related to the vaccine strain. Nationally, 98.8% of influenza A (H1N1) isolates tested for antiviral resistance are resistant to oseltamivir. All of the influenza A (H3N2) and influenza B isolates tested are sensitive to oseltamivir. No resistance to Zanamivir has been detected among any influenza isolates. With regard to adamantanes, 0.6% of influenza A (H1N1) and 100% of influenza A (H3N2) isolates are resistant. Influenza antiviral drug treatment is most important for patients at high risk for severe complications of influenza infection (i.e., patients requiring hospitalization). Empiric treatment recommendations include Zanamivir alone or oseltamivir in combination with rimantidine. Please review our DEC 2008 Advisory and CDC's Interim Recommendations for the Use of Influenza Antiviral Medications (see below). Not all pharmacies stock Zanamivir and rimantadine, consider checking in advance if prescribing these drugs. Resources:
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