The nation's annual influenza outbreak, which started in the 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 remaining 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.
Kaiser Medical Center in Santa Rosa has vaccinated nearly 52,000 patients, along with 98 percent of the medical staff, said Dr. Gary Green, chief of infectious diseases.
"Get it now before the season peaks," he said.
"There is still time; we are not in the midst of it (flu season) yet," said Dr. Karen Holbrook, Sonoma County deputy health officer, noting that seasonal influenza is "just starting to arrive" in California.
Laboratory-confirmed flu cases are appearing in the county, but the level is currently minimal, she said.
In Kaiser's Northern California region, flu tests were running 3 percent positive in mid-December, but by Monday had bumped to 16 percent, a level Green characterized as "mild influenza activity."