Oregon's pertussis outbreak surged by 145 cases in the past month.

Doctors this year have

more than 290 cases of pertussis, or whooping cough, triple the number last year by the end of May.

More than a third of the Oregon cases are in Washington County. At least 11 babies have required hospital treatment for the infection.

Oregon has not come close to the

, where doctors have reported more than 1,940 cases this year, up from 154 in the same period last year.

Pertussis is a respiratory infection that can be life threatening for young children. More than half of infants less than a year old who get the disease are hospitalized, and 1 in 5 infants develop pneumonia. Pertussis has killed four Oregon children since 2003, all less than 12 months old.

Before the introduction of a vaccine in the 1940s, more than 5,000 died of pertussis every year in the U.S. The reported number of cases

in the following decades. But pertussis has slowly rebounded since the 1970s.

One reason is the

of adults immunized as children, who have sustained a pool of susceptible carriers. Since 2006, federal health officials have recommended a booster shot, but adult coverage remains less than 10 percent. Although coverage is much higher among children, the anti-vaccine movement has increased the number of vulnerable children in some communities.

Babies who get pertussis are usually infected by parents or family members who may not even realize they have the disease.

Initially, the symptoms are easy to mistake for a common cold: sneezing, runny nose, and mild fever. But after a week or two, the infection can cause severe coughing fits that drag on for weeks. Babies, with tiny and more vulnerable airways, struggle to breathe and may have trouble eating or drinking.

In Oregon, the incidence of pertussis is

under 2 months of age. They are too young to have started the series of vaccinations that prevent infection. That's why public health officials urge families to create a "cocoon" of immunized people around vulnerable infants by vaccinating parents, older siblings, and other caregivers.

Children are protected by a series of doses of a vaccine called DTaP (diphtheria, tetanus, acellular pertussis), starting at age 2 months and finishing by about age 5. The pertussis vaccine for teenagers and adults is single-dose shot called Tdap that also protects against tetanus and diphtheria.

Here's who should get the Tdap vaccine, according to the

:

• Children 7–10 years of age who have not received a complete series of DTaP

• Adolescents 11–18 years of age

• Pregnant women at 20 weeks or later gestation

• All non-pregnant adults

• For adolescents and adults, Tdap can replace one of the Td boosters needed every ten years. However, adults who have not gotten Tdap should be given a dose regardless of the interval since the last Td booster; recent Td does not seem to increase the risk of adverse reactions to Tdap.

Vaccine effectiveness is clear in the low rate of pertussis among fully vaccinated Oregonians last year, shown here as incidence per 100,000. Fully Vaccinated Not vaccinated 6-11 months 0 735 1-3 years 12 920 4-6 years 2 636 7-10 years 24 397 11 or older 3 6

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