Clark County's flu positivity rate has reached its highest level this season, reflecting a nationwide surge in respiratory illnesses that health officials say is not slowing down.

Since Oct. 1, the Centers for Disease Control and Prevention estimates there have been between 29 million and 51 million flu cases nationwide.

From Jan. 26 through Feb. 1 -- the most recent recorded data -- Clark County Public Health reported a flu positivity rate of 37.34 percent out of 1,280 people tested. During the same time period, the CDC reported a national flu positivity rate of 31.6 percent. Washington and Oregon reported positivity rates of 28.7 percent and 23.4 percent, respectively, according to Public Health.

Influenza positivity at or above 10 percent is considered elevated influenza activity, according to Public Health. The period of high activity is considered over when that number drops below 10 percent for two weeks in a row.