Three cases of whooping cough have been confirmed at Mary Lanning Memorial Hospital in children ranging in age from infancy to 12 years old, a hospital official says.

Federal health officials have said cases of whooping cough (search) have been increasing in the United States since the 1980s. Doctors haven't pinpointed a reason, but some suspect the organism might be mutating.

In 2003 there were 15 reported cases of whooping cough in Nebraska, according to the Nebraska Health and Human Services Web site. More than 100 cases were confirmed in Nebraska in 2004.

The infection is not particularly dangerous to healthy adults, but it could lead to death in unvaccinated infants.

In populations around the world that have not been immunized, whooping cough causes an estimated 300,000 deaths per year. Before age 7, children in this country should get five doses of DTaP vaccine. Immunity typically lasts only five to 10 years after the last injection.

Last year, 13 children in the United States died from whooping cough, also known as pertussis. It was a leading cause of childhood death before the arrival of a vaccine in the late 1940s.

If a person becomes infected with whooping cough, he or she will demonstrate three phases of the infection. In the first phase, the infected person will have sinus congestion, a runny nose, a slightly sore throat and a low grade or absent fever. This stage lasts one to two weeks.

As the infection continues, the cough becomes more severe, so the person is not able to take breaths between the coughs. Following coughing spells, the person will gasp for air, which may sound like a whoop. Vomiting may follow the coughing spells in this phase, which can last two to four weeks.

In the final phase, which can last another two to four weeks, the vomiting and whooping gradually lessen.

Whooping cough is highly contagious with up to 90 percent of susceptible household contacts developing the infection. It is spread through liquid droplets from an infected person's coughing.