Few details were available about the infant, who was treated for whooping cough at a hospital in Pocatello, Idaho, before being flown on Wednesday to a medical center in Salt Lake City, where she later died, hospital and state health officials said.

Washington state has seen 1,132 confirmed cases so far this year, up from 961 for all of 2011. Montana has also seen an alarming rise, with 99 cases so far this year, or about double the number recorded during the same period last year.

In Idaho, 31 cases have been reported since January. The state, where the per-capita occurrence has usually risen higher than the national average since 1987, recorded its last infant death from whooping cough in 2009.

The disease, also known as pertussis, causes severe coughing attacks and is especially dangerous for infants who are younger than a year old and have yet to complete the full cycle of vaccinations against the ailment.

Worldwide, it infects 30 million to 50 million people a year and kills about 300,000 - mostly children in the developing world.

The death in Idaho and the spike in whooping cough cases elsewhere have led health officials to renew a call for the vaccination of children, and boosters for adults who are in contact with babies and young children.

"When you have something as tragic as the death of an infant, it underscores the fact that there are really nasty, severe illnesses that vaccines can prevent," said Emily Simnitt, spokeswoman with the Idaho Department of Health and Welfare.

Idaho and Washington are among 20 states that grant so-called philosophical exemptions to vaccination.

In Ravalli County in western Montana, the number of school-age children who have gained exemptions on religious or medical grounds from vaccinations caused health officials there to request 115 students stay home for three weeks - a period slated to end May 13 - to avoid contracting whooping cough.

Historically, Idaho and other Western states have had lower immunization rates for children ages 19 to 35 months. But disease experts said there was no definitive link between those rates and outbreaks of preventable illnesses.

(Editing by Edith Honan and Peter Cooney)

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