The number of cases is three times greater than those reported last year to date. It has been doubling every month for the last three months, according to the Santa Clara County Department of Public Health.
Pertussis, or whooping cough, is a severe bacterial illness characterized by long coughing fits that often end in a whooping sound when the patient breathes in. The illness is spread through respiratory droplets and can last weeks to months, ranging from six to 10 weeks. Coughing can be so severe that it interferes with eating, drinking and breathing. Treated with antibiotics, pertussis can nonetheless be fatal to infants, officials said.
It is "too early to say whether the recent increase in cases reported in Santa Clara County and the Bay Area herald the next statewide peak," said Dr. Marty Fenstersheib, county chief health officer, who sent a June alert to physicians and hospitals.
Many other states had epidemics in 2012, health department officials said. California experienced a pertussis epidemic in 2010, with more than 9,100 reported cases.
Santa Clara County had 101 cases as of June 21, compared to 46 for all of last year.
There were 461 in 2010 — the most recent epidemic year — and 169 in 2011.
Only 32 cases were reported in 2009, according to county records.
Palo Alto Medical Foundation has had approximately 60 cases confirmed by laboratory tests, Dr. Charles Weiss said.
"Santa Clara County — and in particular Palo Alto — has a lot of cases. I don't know why. One peculiar feature of the disease is that it comes back every three to five years, so the timing is right," he said.
Palo Alto High School had an outbreak in 2006, he said. The epidemic in 2010 "was the worst we had seen in 50 years," he said.
This year, it's middle school kids who have been getting pertussis, Weiss said. The average age has been about 13. A newborn and a 90-year-old patient also contracted the disease, he said.
So far there have been no severe cases, to Weiss's knowledge.
"We have admitted to the hospital a couple of infants who tested positive just to be on the safe side," he said.
Most years, Lucile Packard Children's Hospital sees five or fewer children with pertussis. The majority of cases are under 1 year of age, said Dr. Yvonne Maldonado, chief of the division of pediatric infectious diseases at the Stanford School of Medicine and Packard Hospital.
The severity varies.
"Some have been very ill; others have been primarily admitted for observation and treatment. Any infant under 3 months of age diagnosed with pertussis should be hospitalized, and this is based on an American Academy of Pediatrics recommendation. Usually, the very youngest infants, under 3 months of age, are most severely affected and can be hospitalized for some weeks," she said in an email.
Local medical providers have been focusing on preventing infants' exposure to pertussis. Infants receive a series of vaccinations (DTaP) that protect against diphtheria, tetanus and pertussis. A booster shot called "Tdap" is given to pregnant women, Weiss said.
Fenstersheib said vaccinating women during each pregnancy is crucial. Every pregnant woman should receive a Tdap shot at 27 to 36 weeks. The booster gives the mother protection and provides antibodies to the baby in his or her first six months of life, he said.
But recent studies indicate that immunity from DTaP and from contracting pertussis wanes within a few years.
The Tdap booster shot should be given at age 11, according to public health experts. Preteens, teens and adults should receive the Tdap booster if they have not had one.
So far, health officials are not recommending people get additional pertussis boosters if they've already had one, he said.
The health department recommends that any patient who has the following symptoms be tested for pertussis:
* paroxysms of coughing (multiple coughs in a row without a pause for a breath in between coughs); or
* whooping sound made when taking a breath at the end of the coughing paroxysm; or
* vomiting after the coughing fit; and
* no other explanation for symptoms, such as cold-like symptoms that typically precede a cough; fever is usually absent.
Any pregnant woman in her third trimester who has an acute cough illness more than five days without other explanation should be tested.
Infants younger than 6 months old with pertussis might have no apparent cough, but there could be episodes when the infant's face turns red or purple.