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CDC Report: Flu at Epidemic Levels in U.S.

Illness is deadly for children

According to the Centers for Disease Control and Prevention (CDC), flu activity continues to increase in the U.S. and is high in about half of the country, with national influenza-like illness (ILI) now approaching the peak level seen during the 2012–2013 season. Flu activity is expected to continue in the coming weeks, with increases occurring especially in those states that have not yet had significant activity.

For the week ending December 20, the proportion of people seeing their health care providers for ILI increased to 5.5% and is above the national baseline (2.0%) for the fifth consecutive week.

In addition, a total of 2,643 laboratory-confirmed influenza-associated hospitalizations have been reported through the Influenza Hospitalization Surveillance Network since October 1. That translates to a cumulative overall rate of 9.7% hospitalizations per 100,000 population.

The hospitalization rate in people 65 years of age and older is 38.3 per 100,000. That is the highest rate of any age group. In comparison, the hospitalization rate for people 65 years of age and older for the same week during the 2012–2013 flu season was 28.4 per 100,000.

The proportion of deaths attributed to pneumonia and influenza increased again for the week ending December 20 and was at the epidemic threshold of 6.8%.

Four flu-related pediatric deaths were reported to the CDC during the week ending December 20. Three deaths were associated with an influenza A (H3) virus, and one death was associated with an influenza B virus. To date, a total of 15 influenza-associated pediatric deaths have been reported for the 2014–2015 season.

Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the U.S. during the week ending December 20 increased again to 28.1%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for flu viruses ranged from 11.3% to 35.9%.

Influenza A (H3N2) viruses have been most common in the U.S. this season, the CDC reports. Few influenza B or influenza A (H1N1) pdm09 viruses have been detected. During the week ending December 20, 97.3% of the 6,152 influenza-positive tests reported to the CDC were influenza A viruses, whereas only 2.7% were influenza B viruses. Of the 2,023 influenza A viruses that were subtyped, 99.9 % were influenza A (H3) viruses and 0.05% were influenza A (H1N1) pdm09 viruses.

Since October 1, the CDC has tested 248 influenza A (H3N2) viruses, 55 influenza B viruses, and 11 influenza A (H1N1) pdm09 viruses for resistance to the neuraminidase inhibitors oseltamivir (Tamiflu, Genentech), zanamivir (Relenza, GlaxoSmithKline), and peramivir (Rapivab, BioCryst Pharmaceuticals). All of the viruses showed susceptibility to these treatments. On the other hand, high levels of resistance to the adamantanes –– amantadine (Symmetrel, Endo Pharmaceuticals) and rimantadine (Flumadine, Forest Pharmaceuticals) –– continue to persist among influenza A (H1N1) pdm09 and influenza A (H3N2) viruses. Adamantanes are not effective against influenza B viruses.

Source: CDC; December 30, 2014.

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