For the week ending Nov. 23, there were five states, along with Puerto Rico, at the highest level of the Centers for Disease Control and Prevention’s 1-10 scale of flu activity. That’s more than any year since 2012, including the pandemic season of 2017-2018, according to CDC data, and may suggest either an early peak or the beginning of a particularly bad winter.
“Nationally, ILI [influenza-like illness] activity has been at or above baseline for 3 weeks; however, the amount of influenza activity across the country varies with the south and parts of the west seeing elevated activity while other parts of the country are still seeing low activity,” the CDC’s influenza division said in its weekly FluView report.
The five highest-activity states – Alabama, Georgia, Louisiana, Mississippi, and Texas – are all at level 10, and they join two others – South Carolina and Tennessee, which are at level 8 – in the “high” range from 8-10 on the ILI activity scale; Puerto Rico also is at level 10. ILI is defined 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 CDC said.
The activity scale is based on the percentage of outpatient visits for ILI in each state, which is reported to the CDC’s Outpatient Influenza-like Illness Surveillance Network (ILINet) each week. The national rate for the week ending Nov. 23 was 2.9%, which is above the new-for-this-season baseline rate of 2.4%. For the three previous flu seasons, the national baseline was 2.2%, having been raised from its previous level of 2.1% in 2015-2016, CDC data show.
The peak month of flu activity occurs most often in February – 15 times from 1982-1983 to 2017-2018 – but there were seven peaks in December and six each in January and March over that time period, along with one peak each in October and November, the CDC said. The October peak occurred during the H1N1 pandemic year of 2009, when the national outpatient ILI rate climbed to just over 7.7%.