California is facing what could be the state's biggest outbreak of pertussis since 1958, according to its top public health official. This contagious disease is more commonly known as whooping cough due the distinctive whoop that occurs when sufferers cough and gasp for breath.
"Whooping cough is now an epidemic in California," said Dr. Mark Horton, director of the California Department of Public Health, in a statement. "Children should be vaccinated against the disease and parents, family members and caregivers of infants need a booster shot."
As of June 15, a total of 910 cases had been confirmed in the state. Another 600 suspected cases are currently being investigated by local health officials, the statement indicated.
The number of pertussis cases is now on a pace to surpass the total of 3,182 seen in the most recent major outbreak, which occurred in 2005, said Ken August, spokesman for the department.
August told MedPage Today that 1,200 cases were recorded in 2005 as of mid-June, meaning the state would probably exceed that this year.
The highest yearly total on record is 3,837 cases, seen in 1958.
So far this year, five children have died, all infants younger than three months.
Dr. Blaise Congeni of Akron Children's Hospital in Ohio said he wasn't surprised, as higher-than-usual numbers of pertussis cases have been reported across the country.
"We are having an outbreak in Ohio," though not as severe as in California, he said.
Oregon public health officials have also reported an unusually high number of pertussis cases in that state.
Both Congeni and August noted that pertussis tends to wax and wane in cycles. But gaps in vaccination coverage may also be playing a role, particularly in California.
"California is the epicenter of vaccine refusal" in the United States, said Congeni.
Although outright refusal as well as so-called designer schedules for vaccinations that deviate from evidence-based recommendations are occurring throughout the country, including Ohio, "it's not as much as what my colleagues in California tell me," Congeni said.
August explained that California requires that children receive the full slate of vaccinations for pertussis, measles, and other infectious diseases before they can attend school. But the requirement is waived if parents file a "personal belief exemption" (PBE), which need not be based on religion or medical necessity.
He said that the overall rate for PBEs among the state's roughly 7,200 schools is about 2 percent.
But rates are much higher in some schools. Records for 2009 indicated that close to 175 schools had PBE rates of 20 percent or more. A few had rates above 70 percent.
Researchers have found that vaccination rates of at least 93 percent are needed to ensure so-called herd immunity against pertussis, which prevents the disease from spreading quickly to unvaccinated individuals.
However, August said that some parents may use the PBE to withhold just one vaccine from their children. Others may change their minds after filing a PBE and have their children fully vaccinated.