CDC says U.S. pertussis outbreak could be worst in 50 years

The U.S. Centers for Disease Control and Prevention recently reported that the United States is on track to record its worst outbreak of whooping cough in more than 50 years.

There have been 18,000 confirmed cases of the illness so far this year, more than double the number reported at the same time last year. Health officials said a lack of adequate vaccine coverage could be partially responsible for the outbreak, according to

Washington state and Wisconsin have been the hardest hit, with each reporting more than 3,000 cases this year, according to Reuters.

Nine infants have this died this year as a result of the disease, which can be particularly dangerous in children. Most children in the United States are immunized with a vaccine known as DTaP. DTap is administered in a series of shots that can be started at two months of age. There is also a pertussis booster for adolescents and adults known as the Tdap.

The CDC recommends that all children and adults be vaccinated against whooping cough to prevent infection and to protect infants.

"It's most dangerous for babies," Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, said, Reuters reports. "Preventing infant deaths from the disease is our primary national goal."

Of the 27 reported deaths caused by pertussis last year, 25 were infants.