News from the FDA/CDC

Flu activity measures continue COVID-19–related divergence


The 2019-2020 flu paradox continues in the United States: Fewer respiratory samples are testing positive for influenza, but more people are seeking care for respiratory symptoms because of COVID-19, according to the Centers for Disease Control and Prevention.

Influenza-like illness activity level, week ending March 21, 2020

Positive tests of respiratory samples in clinical laboratories were down to 6.9% for the week ending March 21, compared with 14.9% the week before, but outpatient visits for influenza-like illness (ILI) rose from 5.6% of all visits to 6.2% for third week of March, the CDC’s influenza division reported.

The CDC defines ILI as “fever (temperature of 100°F [37.8°C] or greater) and a cough and/or a sore throat without a known cause other than influenza.” The outpatient ILI visit rate needs to get below the national baseline of 2.4% for the CDC to call the end of the 2019-2020 flu season.

This week’s map shows that fewer states are at the highest level of ILI activity on the CDC’s 1-10 scale: 33 states plus Puerto Rico for the week ending March 21, compared with 35 and Puerto Rico the previous week. The number of states at level 10 had risen the two previous weeks, CDC data show.

“Influenza severity indicators remain moderate to low overall, but hospitalization rates differ by age group, with high rates among children and young adults,” the influenza division said.

Overall mortality also has not been high, but 155 children have died from the flu so far in 2019-2020, which is more than any season since the 2009 pandemic, the CDC noted.

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