California is in the midst of a significant outbreak of whooping cough, with the number of cases at the highest point in 30 years, leading to at least seven deaths of babies, according to public health officials.
As of the end of November, doctors had reported 2,169 cases statewide -- roughly triple last year's level, said Celia Woodfill, an epidemiologist with the state Department of Health Services. The figure is significantly higher than estimates officials made earlier in the year.
"Seven deaths in babies," she added, is "a lot more than usual."
More than three hundred cases had been reported in Los Angeles County through September. Over the past five years, the average in the county has been fewer than 100 cases. The number of cases in Orange County increased sharply in 2002, to 97, and has remained at an elevated level since.
Many parents think of whooping cough as a disease that disappeared decades ago after vaccinations became routine in the 1940s. But the illness has been slowly on the rise in the United States for two decades, in part because adolescents frequently outgrow their immunity.
The sharp increase in California this year, however, has health officials puzzled and has taken many school officials by surprise.
"When I first heard it, I thought it was impossible," said Jeanne Huybrechts, principal of the middle school campus at Harvard-Westlake School in Los Angeles, where three students recently were diagnosed with the illness. "This was my first experience with it, and I've been at the school since 1989."
Whooping cough, formally called pertussis, is a bacterial infection that causes intense coughing spells that often end with a "whoop" sound as a patient struggles to inhale. In some cases, the cough is so intense it leads to vomiting.
Particularly in young children, the disease can lead to other infections, including pneumonia or encephalitis, and often requires hospitalization.
The illness is highly contagious -- people can spread the disease a week before they start coughing and up to three weeks afterward, and only brief exposure is needed to transmit it. Antibiotics can make the disease less contagious if doctors catch it within two weeks of the onset of coughing, but the drugs do not actually stop the symptoms, health officials said.
Because pertussis can be hard to diagnose among adolescents and adults, health officials suggest keeping anyone with a persistent cough away from babies who have not yet been fully vaccinated.
"It's being transmitted oftentimes to very young babies before they're fully immunized, maybe from a loved one or grandparent," said Dr. Jonathan Fielding, Los Angeles County's director of public health.
The number of cases nationwide reached a low point in the late 1970s and has been steadily rising since, making whooping cough the only disease for which a childhood vaccine is routinely recommended that is on the rise in the United States.
"It's the most poorly controlled disease among all the diseases for which there has been a vaccine available for some period of time," said Dr. Katrina Kretsinger, a medical epidemiologist with the National Immunization Program at the federal Centers for Disease Control and Prevention.
Part of the rise probably involves more accurate diagnosis and reporting, but health officials believe the actual number of cases is going up.
Outgrowing immunity can make teenagers vulnerable to the illness and allow them to spread the disease. Roughly one-third of the cases in Los Angeles this year have been in people 15 or older. Statewide, the percentage of cases involving adolescents and adults has increased from fewer than 10% in the early 1990s to half now.
This year, federal health officials began recommending a booster shot for teens and adults.
In addition, some children remain vulnerable because they do not receive all the vaccinations that public health officials recommend -- at 2 months, 4 months, 6 months, 15 to 18 months and 4 to 6 years.
There are also signs that more adults are catching whooping cough. Dr. Stanley Shapiro, an infectious-disease specialist who treats adults, said his hospital, Kaiser Permanente Panorama City Medical Center, has seen about 20 adult cases of whooping cough this year.
He can't remember seeing any adults with pertussis in previous years.
"I suspect it's part of decreasing vaccine rates among youngsters," he said of the disease's resurgence. "There's been a lot of negative publicity about vaccines," he added, noting the accusation, which most medical experts dispute, that vaccinations can trigger autism.
"To me, these are very safe vaccines. My three kids got them all," Shapiro said.
Officials of several area schools said they had seen a notable rise in cases this fall. At the Los Angeles Unified School District, Karen Maiorca, the district's director of nursing, said she plans to remind communicable-disease nurses about the problem at a meeting next month.