Incidents of whooping cough, or pertussis, are running about 10 times higher than normal in the state, prompting the California Department of Public Health (CDPH) to declare the disease an epidemic.

Highly-contagious whooping cough is cyclical, peaking every three or four years, so CDPH officials said they weren’t shocked that the numbers are soaring like they last did in 2010. But this year’s outbreak could be exacerbated by a growing movement in the country to avoid vaccines.

The whooping cough vaccine, unlike those for a lot of other diseases such as measles, does not offer lifetime immunity. The CDPH is urging all pregnant women and infants to get vaccinated immediately. “Two-thirds of pertussis hospitalizations have been in children four months or younger,” the agency reported. “Two infant deaths have been reported.”

There have been 3,458 cases of whooping cough (pdf) reported this year as of June 10. That’s more than in all of 2013. Two children have died. More than 800 cases have been reported in the past two weeks.

Incidence is highest in Sonoma, Napa and Marin counties. The Sonoma rate is more than 10 times the state average and double its own very high 2010 rate. It is nearly double the rate of Napa and Marin.  So far this year, kids under 1 and teenagers, led by 15-year-olds, are the hardest-hit age groups. Twenty-one of the 119 cases that have been hospitalized required intensive care.

A study published last September in the journal Pediatrics said that people who refused vaccinations for their children, largely for religious reasons, were 2.5 times more likely to be living in areas where whooping cough showed up.

Although pertussis is cyclical, the study said the 2010 outbreak in California was the worst since 1947. More than 9,160 cases were reported that year, including 10 children who died.

Parents can claim a pertussis exemption for their children in school to avoid vaccinations and it doesn’t take a lot of them to have an effect on the area. Scientists say that once fewer than 95% of people are vaccinated, a community loses “herd” immunity. Only 91% of California kindergartners statewide were vaccinated as of 2010, but researchers found that in some areas, as high as 84% of students received non-medical vaccine exemptions. (Some people cannot be vaccinated because of other medical issues.)

Because the vaccine wears off, older kids are probably more susceptible, as are adults who didn’t receive a booster shot.

Although nobody wants to hear the word “epidemic” in news reports, health officials pointed out that it refers to an abnormal increase in incidents, not a public health emergency.   

–Ken Broder

To Learn More:

California Whooping Cough Cases Now Labeled an Epidemic (by Tracy Seipel, San Jose Mercury News)

Whooping Cough Reaches Epidemic Level in California (by Monte Morin, Los Angeles Times)

California Experiencing a Whooping Cough Epidemic (California Department of Public Health)

Whooping Cough Cases in State Soar Despite Change in Vaccine Law (by Ken Broder, AllGov California)     

California Whooping Cough Epidemic Connected to Anti-Vaccine Parents (by Ken Broder, AllGov California)

Pertussis Report (California Department of Public Health) (pdf)