This year not only beats a notable 2006 outbreak, it's also "the worst year for pertussis we've had since 1946, since the pre-vaccine era," said Valoree Vernon, an epidemiologist with the Utah Department of Health.
That could be due to better testing and more awareness of pertussis; it is known the disease spreads in waves.
Whooping cough is most dangerous to children under age 1 because they can't be fully vaccinated. They may not cough, but they can stop breathing.
No Utah children have died this year, though one child from Idaho died at Primary Children's Medical Center in Salt Lake City, according to the state. A handful of children have also been hospitalized.
"We can't afford to let these deadly diseases make a comeback," said Charles Pruitt, emergency room doctor and medical adviser for child advocacy at Primary Children's.
Intermountain Healthcare facilities have seen a doubling in the number of positive pertussis cases since April.
"It should have been eradicated by now," Pruitt said, "but there's still a group of people out there that don't immunize so it keeps it brewing at a low level."
Nationally, this year is considered the worst whooping cough outbreak in 50 years, with about 29,000 cases reported to the Centers for Disease Control and Prevention (CDC) through Sept. 20, resulting in 14 deaths. Washington, Minnesota and Wisconsin have each logged about 4,000 cases this year. And Colorado declared an epidemic with nearly 900 cases.
Like those states, Utah has a higher rate of the bacterial respiratory infection than the nation. The state saw a major jump in cases this year in the spring and summer. It's hard to know if that trend will continue. Since the bacteria are passed through coughing and sneezing, the number of cases may grow during the cold months when people are in close quarters.
In past years, the number of cases remained low during the winter. But last year, they jumped during the fall and winter.
Brian Hatch, epidemiologist at Davis County Health Department, saw fewer cases last month than in the summer. "But we're hearing anecdotally … that decrease is due to doctors treating and not testing," he said. "Going back to school you should see that increase in cases because of the close proximity."
Children entering school are required to be vaccinated against the disease, with five doses of the DTaP vaccine.
But a recent study found that DTaP is not as effective as previously thought. The New England Journal of Medicine found the vaccine's effectiveness drops from 95 percent to 71 percent within five years after the fifth dose, which is usually given to children between ages 4 and 6.
That means they would become more vulnerable to catching the disease at ages 9 through 11.
In Utah, children ages 5 to 14 have the second-highest rate of whooping cough. (The highest rate is among infants under age 1 because they can't be fully immunized.) Incoming seventh-graders must get a booster shot, called Tdap, but it's unclear how long that immunity lasts, said Hatch, which may be why the majority of cases in Davis County are among teens.
Nevertheless, public health officials say the vaccine is still the best way to protect the vulnerable. The CDC recommends adults get Tdap boosters as well.
"There's clear evidence the vaccine's the best thing we've got," said Ilene Risk, epidemiologist for the Salt Lake Valley Health Department.
She also said people who have a long-lasting cough should be seen by a doctor. They can be treated with antibiotics but it needs to be done within three weeks of getting sick, according to the CDC.
Prevention: Get vaccinated
The Centers for Disease Control and Prevention say the best way to prevent pertussis is to get vaccinated. There are vaccines for infants, children, preteens, teens and adults.
The Utah Department of Health offers a list of vaccination sources.
The CDC also advises keeping infants and family members at high risk for pertussis complications away from anyone who is infected.
Past coverage of whooping cough in Utah
Whooping cough numbers explode in Salt Lake City, Jan. 10, 2012
Whooping cough continues to menace Utah, May 26, 2012
Whooping cough cases 'raging' through Utah, July 17, 2012
Symptoms of pertussis
Symptoms usually develop within seven to 10 days after being exposed, but sometimes not for as long as six weeks.
Early symptoms can last for one to two weeks and usually include a runny nose, a low-grade fever, a mild occasional cough, and in infants, apnea a pause in breathing.
Infected people are most contagious up to about two weeks after coughing begins.
Antibiotics may shorten the time someone is contagious.
Later symptoms include fits of coughing, followed by a high-pitched "whoop," vomiting and exhaustion.
Source: Centers for Disease Control and Prevention