CDC: Influenza-like illness rates reaching 4.2% nationwide

ATLANTA — The incidence of influenza continued on an upward trajectory heading into the Christmas holiday, the Centers for Disease Control and Prevention reported Friday. Nationwide for the week ending Dec. 22, 4.2% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network were due to influenza-like illness, above the national baseline of 2.2%. 

New York City and 16 states experienced high ILI activity, primarily across the south, while eight states experienced moderate ILI activity. States along the West Coast reported minimal ILI activity. 

Data collected in ILINet are used to produce a measure of ILI activity by state. Activity levels are based on the percent of outpatient visits in a state due to ILI and are compared to the average percent of ILI visits that occur during spring and fall weeks with little or no influenza virus circulation. Activity levels range from minimal, which would correspond to ILI activity from outpatient clinics being below the average, to high, which would correspond to ILI activity from outpatient clinics being much higher than average.

ILI is defined as fever (temperature of 100°F or greater) and cough and/or sore throat. Region specific data is available here.