Recent cases of whooping cough puzzle experts

Doctors and public health officials are stumped. Even though vaccination rates are at record highs for whooping cough, cases of the highly contagious respiratory illness have been on the rise in California and nationwide for more than two decades.

In recent weeks, outbreaks have taken hold in parts of New York, Pennsylvania, Texas and Illinois. Nationally, cases reached 9,771 last year (the most since 1964) -- 1,120 of those were in California.

The disease can be deadly, especially in babies. Five of the 22 deaths nationwide last year were in California. “It’s all in infants, which is really tragic,” said Dr. Howard Backer, the state’s top immunization official.

Whooping cough, or pertussis, takes its name from the sound that infected infants make as they struggle to inhale. It’s caused by a rugged and wily bacterium, Bordetella pertussis, that evades much of the body’s disease-fighting system while wreaking havoc in the lungs, creating paroxysms of coughing powerful enough to break ribs.

In infants especially, coughing fits can lead to vomiting, which can cause malnutrition; complications include pneumonia and death. In adults, the illness typically is less severe, producing a cough that lasts weeks to months.

Vaccination begun in the 1940s was considered to have vanquished the bacterium. It slashed rates from 150 reported cases per 100,000 Americans to less than 1 case per 100,000. But that rate has bounced back to 2.7 reported cases for every 100,000 Americans, although “there may be as many as 10 times as many cases,” said Kris Bisgard, a medical epidemiologist with the federal Centers for Disease Control and Prevention in Atlanta.

The illness is likely to be missed in teenagers and adults, who account for 50% of reported cases, because few doctors are trained to think about pertussis in anyone but babies. Although a simple blood test could help ensure that cases are properly treated, such a test remains elusive. Nor is there a vaccine for people older than 7.

Health officials understand why some people may be susceptible, but they’re at a loss to explain the steady rise in cases. “We’re not 100% sure what the factors are,” Backer said.

Some regional health officials have blamed parents who choose not to vaccinate their children. That has left some children vulnerable both to infection and to becoming potent disease-spreaders. Another problem is that the childhood vaccine is imperfect, just 85% effective against serious forms of the illness. “That means you can get a mild illness if you’re vaccinated and transmit it,” said Bisgard.

Another contributor, she said, is waning immunity: The vaccine probably protects for about 10 years, which means kids become susceptible again by adolescence. (That accounts for outbreaks in junior high and high school.) By the time they’re adults, their only real immunity may be the result of having been unknowingly infected.

Because the five-dose vaccine series begins at 2 months (with additional shots at 4, 6, and 15 to 18 months and again at 4 to 6 years), the deadliest cases are occurring in newborns. Although adults may suffer less, they need to be vigilant because they could still be transmitters.

“If someone has a cough that’s worse after a week, they need to seek medical care,” said Backer. “If you wait too long, antibiotics have minimal effect.”

The only antibiotics effective against it are erythromycin and other macrolides, including azithromycin (Zithromax) and clarithromycin (Biaxin). An alternative is a combination antibiotic, trimethoprim-sulfamethoxazole, (Bactrim, Septra).