(CNN) -- 2012 might be a record year for whooping cough in the United States if midyear trends continue. Nearly 18,000 cases of pertussis, or whooping cough, have been reported to the Centers for Disease Control and Prevention so far this year - the highest rates in five years.
"That's more than twice as many as we had at the at the same time last year," said Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the CDC. "We may need to go back to 1959 to find a year with as many cases reported by this time so far, " she said Thursday.
Pertussis is a highly contagious illness caused by a bacterium called Bordetella pertussis. It easily spreads from person to person when people cough or sneeze. It starts out with symptoms very similar to a cold, but a week or two later, a violent cough develops. It's better known as whooping cough because of the "whooping" sound those infected make when they are violently coughing over and over again and try to inhale.
The cough can last for weeks, and children can cough so hard and rapidly that blood vessels can burst. They have difficulty eating, drinking and breathing.
Young children are particularly at high risk for serious complications. Schuchat says so far nine babies have died from pertussis this year. She adds that the highest rates of illness have been seen in babies younger than 1, and half of those cases have been infants younger than 3 months old.
Whooping cough is vaccine preventable, but newborns can't get the first dose of vaccine until they are 2 months. Then they need four more vaccinations before they turn 7 to get full protection. This is why young children are highly dependent on the people close to them to be vaccinated so they don't pass the disease on to them.
"We strongly urge pregnant women and all who will be around babies to be vaccinated. Infants often get pertussis from a family member or household member," said Schuchat. The latest CDC data suggest only 8% of adults get a booster vaccine against pertussis.
Schuchat says many states are seeing higher than expected cases of pertussis.
One of the states hit hard in this wave of disease is Washington. In April, the Washington State Department of Health declared an epidemic . The department is reporting 3,014 cases as of July 14 -- a 1,300% increase compared with the same time in 2011, when they reported 219 cases. Health Secretary Mary Selecky said: "We are seeing the largest number of cases in our state since the early 1940s."
Wisconsin is reporting 3,022 confirmed and probable cases so far in 2012.
Schuchat says pertussis cases go up and down in waves. She says if the number of cases continue to grow, "we may be on track for record high pertussis rates this year." The last time whooping cough rates were climbing in the U.S. was in 2010, when 27,550 cases of pertussis were reported to the CDC.
In addition to high rates of illness among of babies, new data published Thursday in the CDC's "Morbidity and Mortality Weekly Report," shows high rates of whooping cough among 13- to 14-year-old adolescents in Washington. Schuchat says this is something health officials are seeing nationwide as well and is different from previous pertussis outbreaks.
Why this is happening isn't entirely clear. Schuchat suggests waning of immunity or a weakening of the protection over time might be part of the what's contributing to these teens getting sick.
Health officials acknowledge that vaccines are not perfect, but they do provide the best protection against whooping cough. So the CDC is emphasizing the importance of young children getting their five pertussis vaccinations, then getting the recommended booster shots between 11 and 12 and that adults who will be around babies also getting vaccinated.
"In 2010, only 8% of adults had any history of receiving a Tdap booster," said Schuchat.
She suggests that clinicians who see patients with a persistent cough consider pertussis as a diagnosis. Then she says doctors should "be proactive with treatment, especially with pregnant women, infants and others who are around infants."
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