Doctors are recommending that just about everyone in the United States between the ages of 11 and 64 -- especially people who regularly interact with newborns -- get booster shots of the whooping cough vaccine to help battle recent increases of a disease that once was thought to have mostly disappeared.

The vaccine for whooping cough, also known as pertussis, is given to children five times between ages 2 months and 6 years. But the protection wears off just five to 10 years after the last dose, meaning adults who got their childhood vaccination are susceptible to the disease, and even children in middle school and high school are vulnerable, say the American Academy of Pediatrics and the Centers for Disease Control and Prevention.

Cases of whooping cough more than tripled in the United States between 2001 and 2004, according to the CDC. In San Francisco, the number of cases increased by about 60 percent in 2005 over the previous year.

Whooping cough, which got its name from the noise children make when they gasp for breath between violent coughs, is an exhausting and annoying respiratory infection but is not necessarily dangerous in adults and teenagers.

But it can be fatal to young children and babies, who develop terrible coughs that can lead to vomiting and severe dehydration, along with pneumonia, seizures and brain damage in very serious cases. In 2005, seven babies died in California from whooping cough; one baby has died this year.

"The people who suffer the most are the really small ones. They're the ones who die, and they get it even before they're able to get the doses of vaccine," said Celia Woodfill, chief of the immunization branch for the California Department of Health Services. "The people that we would really like to target with this vaccine are people who are going to be parents and extended family of new babies. They call it the cocoon strategy -- we want to protect those babies by vaccinating all the people around them."

Health care experts have long known that whooping cough immunization wouldn't last forever, but for decades physicians didn't bother with a booster shot after age 6. This was because of the side effects of the vaccine -- a lingering fever and intense soreness at the injection site -- and the fact that the disease isn't usually serious in adults.

In the 1980s, scientists developed a better whooping cough vaccine without the side effects, but it was approved only for children. It wasn't until last year that the newer vaccine was approved for adults up to age 64. The vaccine became widely available outside pediatricians' offices just this year.

Still, many physicians who treat only adults aren't giving the whooping cough booster to patients because the vaccine is so new. Health care experts advise adults to insist on the whooping cough vaccine when they go in for their tetanus booster, which is recommended every 10 years.

Adults who have regular contact with newborns -- especially parents, day-care workers and health-care workers -- should get the booster right away, health officials say. Many obstetricians are encouraging entire families -- including extended family members like grandparents who may spend a lot of time with a newborn -- to get booster shots immediately after a baby is born. In March, health officials recommended that all 11- and 12-year-old children receive a whooping cough booster.

"If you see whooping cough in a baby, it's almost always from a mother or a close household contact -- a nanny, a grandma," said Peggy Weintrub, chief of pediatric infectious diseases at UCSF. "There is a push to give this to more people because it's clearly recognized that they're the ones exposing the infants."

Whooping cough made a major resurgence in the United States about five years ago, although the number of cases has been growing every year for the past decade or so. There were 25,827 cases in the United States in 2004 -- way up from the all-time low of 1,010 cases in 1976.

California had 3,172 cases last year and 1,013 cases by the end of August this year -- slightly below last year's 1,276 by the end of August.

San Francisco had 45 cases last year, up from 28 cases in 2004. In 2005, 34 people between the ages of 15 and 54 got whooping cough, compared to 10 in 2004.

San Francisco had reported 25 cases of whooping cough by Aug. 11 this year.

"There's pertussis everywhere, and we're still only detecting the tip of the iceberg," Woodfill said. "We think that actually there's much more disease in adults and adolescents, and they're the ones giving it back to the babies."

The reason whooping cough has been so persistent despite massive immunization efforts in the 1960s and 1970s is that as immunity wore off, enough of the disease remained that it was able to easily spread again.

Also, before the vaccine existed, the vast majority of children and adults kept up a natural immunity over their lifetime because the disease was so prevalent and they were constantly being exposed to it. Mothers were even able to pass on some of that immunity to their newborns.

Physicians also assume that cases of whooping cough probably were underreported during the 1980s and 1990s, when doctors assumed the disease was all but gone and weren't looking for it. In many cases, whooping cough probably was misidentified as bronchitis or, simply, a bad cough. It's only with recent new focus on whooping cough that doctors are reporting more cases of it.

"There are some diseases, like smallpox and polio, that the vaccine could eliminate the disease. But whooping cough, we don't have an immunization that is effective enough that if you gave everyone the vaccine, it would just disappear," said San Francisco pediatrician Dan Kelly. "There will always be a reservoir of whooping cough among people.

"We've let the resistance level in adults get much too low. Childhood immunizations, it turns out they're not just for children."

About the disease

Whooping cough, also known as pertussis, is a highly contagious respiratory infection that causes violent coughing.

Cause: The Bordetella pertussis or B. parapertussis bacteria are spread via coughing and sneezing from an infected person. Symptoms show up a week after exposure and can be similar to the common cold.

Dangers: Whooping cough can be fatal in infants. It also can lead to severe dehydration, pneumonia and brain damage in infants who cannot catch their breath, or who cough so much they vomit. Severe coughing can cause broken ribs in patients of all ages.

Symptoms: Signs of the illness include a high-pitched whooping sound when the patient gasps between coughs, runny nose, slight fever, diarrhea and choking spells.

Treatment: Antibiotics. Cough expectorants and suppressants are not recommended.