U.S. flu reaches U.S. baseline ATLANTA, March 24 (UPI) -- Influenza activity has been increasing, reaching the U.S. normal annual baseline level, 2.4 percent, during the week ending March 17, health officials said. Of the 5,088 specimens from patients presenting during the week with influenza-like illness and tested by U.S. World Health Organization and National Respiratory and Enteric Virus Surveillance System laboratories, 26.6 percent were positive for influenza, the Centers for Disease Control and Prevention said in a report. Baseline level is the rate of influenza-like illness that is reported year-round. The level of influenza-like illness usually rises much higher during the flu season of October to May. Influenza-like illness is defined as a fever of 100 degrees F. or more, cough and/or sore throat, in the absence of a known cause. These data are transmitted once a week the CDC. Region 5: Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin increased from 46.3 percent to 60.7 percent reporting influenza-like illness. Region 7: Iowa, Kansas, Missouri and Nebraska increased from 34 percent reporting influenza-like illness last week to 39.2 percent. Arizona, California, Colorado, Illinois, Iowa, Kansas, Kentucky, Maryland, Michigan, Minnesota, Missouri, Nevada, New Jersey, New York, Oklahoma, Pennsylvania, South Dakota, Utah, Washington and Wyoming reported widespread influenza activity. Twenty states reported regional activity, two states reported local activity and eight states, Guam, the District of Columbia and New York City reported minimal influenza-like illness, the CDC said.