The Centers for Disease Control is pointing to Washington state's whooping cough epidemic as an example for the rest of the nation as infection rates rise.
Nationally, 18,000 people have been diagnosed with whooping cough, or pertussis -- more than twice last year's total.
In Washington, a total of 3,014 cases have been reported so far this year. Last year at this time, just over 200 cases were reported in the entire state.
"This is more than a Washington State story," said the CDC's Dr. Anne Schuchat. "I think we're in for a tough year and a tough couple years."
National rates of whooping cough are on track to match levels last seen in 1959.
Scientists are particularly interested in infections among young teens in Washington, between the ages of 10 and 13. Doctors have noticed a slight upswing in infections within the age group. It's not yet known whether that can be attributed to waning protection from vaccines received at an early age, or a varying strain of the disease. The CDC plans to study the observations further.
"Vaccination is still the very best protection, that's why we want everyone to make sure they're up to date on their whooping cough vaccine," said Mary Selecky, Washington's Secretary of Health.
Doctors recommend the Tdap booster vaccine for everyone over the age of 11. However, only 8 percent of the nation's adults aged 19 to 64 received the shot in 2010, according to the CDC.
Campaigns in Washington to get more people vaccinated are primarily focused on pregnant women and people who work around children.
"We need more help from adults in Washington state," said Selecky.
Skagit County has the highest number of reported pertussis cases. Here's more on the status of whoopoing cough in Washington.
Infection rates tend to rise and fall every three to five years, according to Dr. Schuchat.
Pertussis is a highly contagious bacterial disease. It causes children to make a whooping sound as they gasp for breath.
In rare cases it can be fatal. The CDC reports nine children have died from it so far this year.
KING 5's Jean Enersen and the Associated Press contributed to this report.