From Reuters Health Information
By Laura L. Myers
SEATTLE (Reuters) Jul 20 – The number of U.S. whooping cough cases has risen to around 18,000 in an outbreak that is on track to become the most severe in over a half century and could in part stem from possible waning vaccine protection, health officials said on Thursday.
Washington state, which declared an epidemic in April, and Wisconsin were particularly hard hit, with each reporting more than 3,000 cases, according to the U.S. Centers for Disease Control and Prevention.
Nine people have died overall and the number of cases was already more than double than at the same time last year.
All adults, including pregnant women, should get a booster shot because the contagious illness is especially dangerous for children under a year old who have yet to complete a cycle of vaccinations, Dr. Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases, told a media briefing.
"It’s most dangerous for babies," Dr. Schuchat said, adding that the current outbreak at its existing pace could become the most severe since 1959, when 40,000 cases were reported. "Preventing infant deaths from the disease is our primary national goal," she said.
A spike in pertussis cases among 10-, 13- and 14-year-olds was a concern, perhaps an indicator that the pertussis vaccine may be wearing off earlier than anticipated, Washington Health Secretary Mary Selecky said.
The U.S. groups of 10-, 13- and 14-year-olds who are experiencing a high illness rate had DTaP vaccinations, which were introduced in 1997 at the same time that the prior DTP vaccine was discontinued.
The earlier vaccine used whole cell parts made of killed pertussis bacteria, while DTaP uses only small acellular bacteria pieces, not the whole bacteria cell, said Donn Moyer, Washington state Health Department spokesman
CDC officials will begin an investigation in Washington state later this month "to analyze our data for cases among 13- to 14-year-olds to see what can be learned about disease rates and vaccination status," Moyer told Reuters.
The number of cases in Washington, with no deaths, has tripled since April, with 1,132 cases reported by the end of that month.
Moyer said the CDC also plans a similar study in California, where a 2010 epidemic counted more than 9,000 cases, including 10 infant deaths.
Earlier this week, New York state released preliminary figures showing 970 cases so far in 2012. In all of 2011, there were 931 cases reported in New York. (See Reuters Health report of July 18, 2012.)
This year, Australia is also experiencing a high rate of whooping cough, Schuchat said.