TUCSON - State health officials say that as of Dec. 15, the number of probable and confirmed cases of whooping cough is up 67 percent from 2010 and up 5 percent from last year and the number has climbed steadily since 2007.
Whooping cough, also known as pertussis, is an infection that can kill otherwise healthy infants. One infant in Arizona died from whooping cough earlier this year.
Dr. Karen Lewis, medical director of the Arizona Department of Health Services' Immunization Program Office, said about one in every 100 infants hospitalized with whooping cough will die.
State officials blame multiple factors for the continued rise in whooping cough, including better awareness and reporting, improved testing and an increasing number of parents who aren't vaccinating their children against the highly contagious disease.
"Anybody who is unvaccinated can help in the spread," Lewis told The Arizona Daily Star "I took care of hospitalized children with infectious diseases for 15 years, and I am concerned when anybody gets sick with a vaccine-preventable disease.
"I am very worried about whooping cough spreading to infants because I have had to take care of children with whooping cough who have died despite doing everything I could do," Lewis added.
A switch from what's called a "whole cell" pertussis vaccine to a more purified "acellular" version has also contributed to the increased number of cases.
The switch, made in the 1990s, appears to be causing the childhood pertussis vaccine to wear off faster than in the past, Lewis said. The change was made to reduce side effects. That's why it's so important for both adults and adolescents to get a pertussis "booster" shot.
But Lewis said the number of adults who have received the federally recommended whooping cough booster remains far too low, particularly among health care workers.
Very few hospitals require their employees to have it, and as a result only 20 percent of health care workers have received the booster. And less than 10 percent of the general adult population has received the booster, leaving the infants they come in contact with extremely vulnerable.
The incidence of whooping cough has not decreased in terms of percentages as much as other vaccine-preventable diseases in recent years, according to Lewis.
"Vaccination doesn't give you 100 percent protection against the disease, but you are much less likely to get infected, and you are much less likely to spread it to other people," she said. "That's why people choosing not to get vaccinated are making not just a personal choice, but a public health choice."
The rise in Arizona whooping cough cases mirrors a national trend. As of Dec. 8, more than 39,000 cases of whooping cough -- double the number in 2011 -- had been reported across the U.S. Nationwide, 16 people died from whooping cough this year.
Arizona's whooping cough rate of 13.5 cases per 100,000 people this year is higher than the national average of 11.6 per 100,000, but much lower than some states including Colorado, Washington and Vermont, which reported epidemic levels.
Before pertussis vaccines became widely available in the 1940s, records show about 200,000 U.S. children got sick with it each year and about 9,000 died.