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Whooping Cough Makes a Comeback

U.S. finds more cases in adolescents and adults

THURSDAY, Jan. 31, 2002 (HealthDayNews) -- Whooping cough, once a terrible scourge of children in this country, was driven all but extinct after World War II thanks to an effective vaccine against the bacterial infection.

But in the last 25 years, according to a new government report, the respiratory disease has climbed off the epidemiological mat and appears to be gaining strength again, especially among adolescents and adults whose immunity against it is waning.

The report by the Centers for Disease Control and Prevention says most of the increased caseload is the result of improved reporting of whooping cough, which is also known as pertussis. Better epidemiological tools to track the infection are also behind the rise.

However, experts say at least some of the trend is almost certainly due to a true jump in prevalence of the illness. While not typically serious, whooping cough can cause life-threatening brain damage, especially in infants.

Whooping cough, caused by the bacterium Bordetella pertussis, was once a major killer of children in the United States. It was tamed by the introduction in the late 1940s of the so-called DTP vaccine, a triplet injection that included protection against diphtheria and tetanus. Over the next 30 years, the annual caseload of whooping cough plunged, hitting an all-time low of 1,010 cases in 1976.

Since then, the disease has made a strong comeback. The latest figures, published in this week's Morbidity and Mortality Weekly Report, show almost 29,134 reported cases between 1997 and 2000, rising unevenly from 6,564 in the first year to 7,867 by the last. Cases among teens and adults jumped 60 percent during the study period over levels in 1994 and 1996, officials say.

Dr. Lynn Zanardi, a CDC medical epidemiologist and a co-author of the study, says much of the surge is due to improved surveillance of pertussis, as well as the introduction of a genetic test, the polymerase chain reaction (PCR), to help labs better identify the germ in patient samples.

However, "the immunity that someone has from the vaccine wanes over time," Zanardi says, allowing unvaccinated or partially immunized children to contract the infection.

The cases include more than 5,600 hospitalizations and 62 deaths from the disease, which can lead to pneumonia, seizures, and the brain inflammation called encephalitis.

Almost all the fatalities were among children under 6 months of age, many of whom probably hadn't received the full battery of pertussis vaccine. Indeed, the number of cases among babies over 6 months of age remained stable during the study period and included only one reported death.

Officials recommend that babies get their first shot at 2 months, followed by another at 4 months, a third two months later, and a fourth shot sometime between 15 and 18 months. That should be followed by a fifth shot between years 4 and 6. The study found that 73 percent of infants between the ages of 7 months and 18 months had received at least three doses of a pertussis vaccine -- a figure Zanardi says is better than in past decades.

Pertussis cases among infants rose 11 percent between 1997 and 2000, but dropped by 8 percent among children ages 1 to 4. Cases also remained steady among children between 5 and 9, according to the report.

While some of the increased caseload is the result of unprotected infants and waning immunity, Dr. Julia McMillan, a Johns Hopkins pediatrician, says that's not the whole story. "Some of those adolescents and adults who get pertussis were never appropriately immunized."

The DTP vaccine (there's also a DT injection) is not recommended for children over the age of 7 because of concerns about adverse reactions to the shot, which in rare instances can include very high fevers, convulsions and collapse. McMillan says there's not enough evidence yet to know if a modified and less reactive shot, called DTaP, is safer in older children.

Zanardi says two companies are now trying to obtain Food and Drug Administration approval to market a version of the pertussis vaccine to people older than age 7. If approved, the products could serve as boosters to existing shots, she says.

What To Do

For more on whooping cough, visit the King County Department of Community and Human Services or the Centers for Disease Control and Prevention.

SOURCES: Interviews with Lynn Zanardi, M.D., medical epidemiolgist, Centers for Disease Control and Prevention, Atlanta; Julia McMillan, M.D., professor of pediatrics, Johns Hopkins University, Baltimore; Feb. 1, 2002, Morbidity and Mortality Weekly Report
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