Dr. Anju Goel, Marin deputy public health officer, said 58 cases of whooping cough, a highly contagious respiratory tract infection also known as pertussis, were reported in Marin from Jan. 1 to May 17, compared with just 19 during 2009.
The higher Marin numbers reflect a statewide phenomenon. According to the California Department of Public Health, 346 pertussis cases were reported in California from Jan. 1 to April 30, up from 129 cases during the same period last year.
Statewide, four newborns have died from whooping cough - two in Los Angeles County and two in the Central Valley. State health officials say pertussis cases tend to be cyclical, with a rise in the number of cases every two to five years followed by a decline.
"The last big outbreak of pertussis cases was in 2005," said Ken August, a state Department of Public Health spokesman. "So we're concerned we could be in for another tough year."
In 2005, pertussis killed eight California infants.
Infants, the elderly and those with weakened immune systems are most at risk. According to the Centers for Disease Control and Prevention, more than half of infants less than 1 year old who get the disease must be hospitalized. About one in 10 children with pertussis get pneumonia, and about one in 250 people who become infected develop a brain disorder called encephalopathy. The disease causes an estimated 10 to 20 deaths each year in the United States.
In Marin, the Ross Valley School District's five campuses in San Anselmo and Fairfax are being hit the hardest.
Laurel Yrun, the district's school nurse, said parents had reported 20 probable cases so far, most of them during May. Yrun said Wade Thomas School in San Anselmo and Manor School in Fairfax have the most cases. She said the district is instructing parents whose children are taking medication to treat pertussis to keep them out of school for five days.
Yrun said by the time parents spot the disease their child has often been infected for several days.
"The symptoms start out like a cold. They're not necessarily having this big whooping cough," Yrun said. "So parents aren't thinking about whooping cough."
Rick White of Novato said two of his grandchildren who attend Manor School and their parents have been diagnosed with whooping cough. White suspects the large number of cases in Marin may be linked to the growing number of parents who refuse vaccinations for their children.
Marin has one of the state's highest rates of personal belief exemptions, parental waivers that allow children to enroll in kindergarten without receiving vaccinations against diseases such as measles, polio or whooping cough.
In 2009, 7.1 percent of the Marin students entering kindergarten avoided immunization because their parents claimed a personal belief exemption, Goel said. Statewide, only 2 percent of kindergartners used the exemption to avoid vaccination last year, she said. In 1999, less than 2 percent of Marin kindergartners opted out of vaccinations.
"This is really unfortunate because we have diseases that are vaccine preventable, such as pertussis," Goel said. "I think some people who chose not to get vaccinated don't recognize that these diseases still exist and can still cause very serious illness and even death."
Susan Goldsborough of Woodacre said, "It certainly concerns me."
Goldsborough said the preschool her granddaughter attends in Fairfax had to close earlier this year because two teachers and several students there contracted pertussis. She is particularly concerned about the danger pertussis poses to her 16-month-old grandson, who suffers from asthma and had pneumonia twice during the winter.
"To get pertussis would be deadly for him," Goldsborough said.
The immunity that vaccinations provide begins to fade after three to five years. State health officials are advising caregivers of newborns to take a new vaccine that became available for adults and adolescents in 2005.
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