News from the FDA/CDC

Flu activity declines again but remains high


Nationwide influenza activity declined for the third consecutive week, but the 2019-2020 season is on pace to be the longest in more than a decade.

Influenza-like illness activity level, week ending Feb. 29, 2020

Outpatient visits to health care providers for influenza-like illness dropped from 5.5% the previous week to 5.3% of all visits for the week ending Feb. 29, the Centers for Disease Control and Prevention said on March 6.

The national baseline rate of 2.4% was first reached during the week of Nov. 9, 2019 – marking the start of flu season – and has remained at or above that level for 17 consecutive weeks. Last year’s season, which also was the longest in a decade, lasted 21 consecutive weeks but started 2 weeks later than the current season and had a lower outpatient-visit rate (4.5%) for the last week of February, CDC data show.

This season’s earlier start could mean that even a somewhat steep decline in visits to below the baseline rate – marking the end of the season – might take 5 or 6 weeks and would make 2019-2020 even longer than 2018-2019.

The activity situation on the state level reflects the small national decline. For the week ending Feb. 29, there were 33 states at level 10 on the CDC’s 1-10 activity scale, compared with 37 the week before, and a total of 40 in the “high” range of 8-10, compared with 43 the week before, the CDC’s influenza division reported.

The other main measure of influenza activity, percentage of respiratory specimens testing positive, also declined for the third week in a row and is now at 24.3% after reaching a high of 30.3% during the week of Feb. 2-8, the influenza division said.

The overall cumulative hospitalization rate continues to remain at a fairly typical 57.9 per 100,000 population, but rates for school-aged children (84.9 per 100,000) and young adults (31.2 per 100,000) are among the highest ever recorded at this point in the season. Mortality among children – now at 136 for 2019-2020 – is higher than for any season since reporting began in 2004, with the exception of the 2009 pandemic, the CDC said.

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