No deaths have been reported from this year's outbreak but 20 infants have been hospitalized with the bacterial infection, which poses a special risk to young children, said Tim Church, a spokesman for the state Health Department.

Governor Christine Gregoire made state emergency funds available on Thursday to help increase vaccinations against the disease and announced federal approval to redirect some funds to buy 27,000 more doses of vaccine for uninsured adults.

Whooping cough, also known as pertussis, causes severe, uncontrollable coughing. Worldwide, it infects between 30 million and 50 million people a year and kills about 300,000 - mostly children in the developing world.

In the United States, most children are immunized against whooping cough with a vaccine that is given as a series of shots starting at the age of two months.

Outbreaks in the United States tend to run in cycles, but Church said the latest wave of cases in Washington state was running well above typical peak years in the past, when 500 to 600 cases might be reported for an entire year.

"We're seeing 100 to 125 new cases every week," he said, adding that at the current pace, Washington could end 2012 with about 3,000 cases, which would be the highest number the state has seen since the 1940s. "Our hope is that we can stem this tide and not let that happen."

The current epidemic appears to have begun last year.

The 1,132 confirmed cases reported year to date through April 28 already surpasses the 961 recorded for all of 2011, though that figure included two infant deaths, Church said.

But it pales in comparison to a 2010 epidemic that hit California, which counted more than 9,000 cases, including 10 infant deaths.

Proportionately, however, 3,000 cases would be a much greater tally for Washington, with a population of about 6.7 million people compared to more than 37 million in California.

Church said Washington state's relatively high rate of vaccine exemptions allowed for school-aged children, which stands at 6 percent, "might be part of the puzzle," but other factors remain unknown.

For now, Washington is the hardest hit state in the country, though pertussis outbreaks also have been reported in Oregon, Idaho and a few New England states, Church said.

(Reporting by Laura Myers in Seattle; additional reporting and writing by Steve Gorman; editing by Dan Whitcomb and Todd Eastham)

• A Permanent Economic Emergency