Flu activity still rising, but CDC warns many weeks of activity ahead

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In a telebriefing this morning, the Centers for Disease Control and Prevention (CDC) said flu activity is at the highest it's been all season, with all parts of the continental United States reporting widespread levels of the virus.

"This is the first year the continental map of the United States is all one color, meaning widespread activity," said Dan Jernigan, MD, MPH, director of the influenza division at the CDC's National Center for Immunization and Respiratory Diseases. "There's a sense across the country that a lot is happening with flu."

Alabama's governor, Kay Ivey, declared a state public health emergency yesterday because of rising flu levels in that state. Elsewhere, there has been widespread media coverage of healthy adults who have died after getting the flu.

But while no one disputes this is a bad year for flu, Jernigan said it's too early to tell if this flu season is more severe than recent seasons, including the 2014-15 season.

"We know this is a very active year, but we don't know yet if it's a severe year," Jernigan said. "So far, 2014-2015 had more severe indicators at this point in the season." And while flu activity may be nearing its peak, Jernigan warned there will still be several weeks of activity, which will likely see more infections caused by influenza B strains.

"People should do everything they can still do to reduce the risk of infection, including getting the flu vaccine," Jernigan said. While most circulating flu is influenza A subtype H3N2, which the seasonal flu vaccine does not perform well against, the vaccine should offer substantial protection for subtypes H1N1 and influenza B. 

Latest markers show hospitalization jump

Hospitalizations have seen a sharp uptick since last week, according to the latest numbers from CDC's weekly update today, which covers the week ending Jan 6.

The overall hospitalization rate was 22.7 per 100,000 population this week, up from last week’s 13.7, the biggest jump so far this season. Adults over the age of 65 were most likely to be hospitalized, at a rate of 98.0 per 100,000 population, nearly doubling last week's rate of 56.6.  Rates for adults ages 50 to 64 were 24.0 per 100,000 population, and children ages 0 to 4 years were 16.0 per 100,000 population.

The vast majority of hospitalizations were due to influenza A infections (90%), with 6% caused by influenza B. the rest were unsubtyped or due to a mix of strains. Of all tested laboratory samples received by the CDC last week, 83.6% were influenza A and 16.4% were influenza B.

The proportion of outpatient visits for influenza-like illness (ILI) was 5.8%, the same as the previous week. Jernigan said that in 2014-15, the last severe flu season in the United States, that number reached 6% at this point in the flu season.

Pediatric flu deaths rise

In one indicator of a worsening season, the CDC reported 7 new pediatric flu deaths. So far this season there have been 20 pediatric deaths, most from influenza A.

Jernigan said clinicians should still give antivirals to patients, especially young children or older adults, at the first sign of suspected flu and not wait until laboratory confirmation. Antivirals can shorten the duration and severity of the flu.

See also:

Jan 12 CDC FluView

Jan 11 Alabama notice

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