The nation's annual influenza outbreak, which started last fall east of the Mississippi River, has swept across the country and is just now arriving in Sonoma County, touching down lightly but expected to grow in impact, local health officials said.
The seasonal flu, measured by reports of influenza-like illness, is approaching a "moderately severe" level nationwide and prompting alerts in the East and Midwest.
In Boston, officials declared a public health emergency on Wednesday, citing a sharp rise in flu cases over last year. In Milwaukee, hospital emergency rooms were diverting ambulances because of an influx of older patients with flu-like symptoms.
The flu's impact remained below the pandemic year of 2009-10, officials said, noting that the vaccine designed as the nation's primary flu defense was proving effective against more than 90 percent of the viruses infecting the public this year.
With about three months remain in the flu season, Sonoma County health officials and physicians urged the public — especially preschoolers, people over 65 and pregnant women — to get vaccinated as soon as possible.