An outbreak of whooping cough has hit Utah, health department officials said Friday.

Fifty cases have been confirmed and hundreds more people are showing symptoms of the infectious respiratory disease pertussis, commonly known as whooping cough.Scott Williams, deputy director of the Utah Department of Health, said 50 Utah people have been diagnosed with whooping cough since January. In the last few months, seven new cases have been reported in four different parts of the state, leading health officials to call attention to the matter.

"When you get a few people exposed, those people can expose other people. It's kind of this geometric expansion," Williams said. "Pretty soon you have enough exposure that the second wave of cases starts to occur."

Ages of those diagnosed range from a newborn to age 55 and they've occurred in Utah, Salt Lake, Summit and Washington counties in the past month.

In Salt Lake County alone, 29 cases of whooping cough have been confirmed and 277 other people are symptomatic and receiving antibiotics, said Kathryn Vedder, director of the Salt Lake City/County Health Department.

"We're very concerned," Vedder said Friday. "Adults are all suspectible to pertussis and are actually going to be spreading the disease to the children."

Children under 2 who are not immunized are most vulnerable to the disease, which can cause pneumonia, brain damage and death. In the past six weeks, two infants have been hospitalized at Primary Children's Medical Center with whooping cough, Williams said. Utah ties with Idaho for last place among states for pre-school immunizations among 2-year-olds.

Whooping cough in children can be prevented by a series of shots given at 2, 4, 6 and 15 months and again when the child enters school.

Because the vaccinations wear off after five to 10 years, adults and adolescents immunized as infants can catch whooping cough and pass it along to others. Adult symptoms are usually less severe. The contagious stage of the disease is shortened by treatment with anti-biotics, Williams said.

Health officials are urging Utahns with a persistent cough to see a physician immediately. Other symptoms include runny nose, sneezing and a low-grade fever. There may also be vomiting and the symptoms last four to six weeks.

"We really want to identify those people, so we can get them on antibiotics and keep them from spreading it around," Williams said.

Whooping cough has been a problem throughout the Intermountain West, Vedder said, though health officials don't know why. Idaho has been especially hard hit.

Vedder said the number of recent cases led her, Williams and other health department directors to meet this week and decide to call the situation an outbreak and start informing the public.

"Anybody with a persistent cough or anybody whose children have persistent coughs and are not immunized needs to immediately call their physician," Vedder said.

Cases of pertussis in 1998 include: Salt Lake County, 29; Utah County, 12; Summit, Davis, Tooele and the Southwest Utah Public Health Department (Beaver, Iron, Garfield, Washington and Kane counties), 2 each; Weber/Morgan area, 1.