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Rising pertussis rates spark new public health concern

Misdiagnoses and undertreatment among adults and adolescents may warrant new vaccination strategies

From the March ACP Observer, copyright 2005 by the American College of Physicians.

By Janet Colwell

Public health officials are warning that pertussis cases are on the rise—and not just among children.

Infants, of course, are particularly vulnerable, especially if they haven't completed their series of vaccinations. According to findings published Dec. 15, 2004 in Clinical Infectious Diseases, the nation's mean annual incidence of pertussis among babies younger than four months has jumped almost 40% in the last 20 years

Many of those cases, health officials claim, may be due to rising rates of pertussis among adolescents and adults. Older patients' immunity from vaccination may wane, experts say. And early pertussis symptoms mimic other upper respiratory conditions, which often leads to misdiagnoses and undertreatment among infected and contagious adults.

Concerns about those trends are leading some public health and infectious disease experts to call for extending booster immunizations through adulthood, according to Kathleen M. Neuzil, FACP, MPH. Dr. Neuzil is an associate professor of medicine at Seattle's University of Washington and the ACP representative to the CDC's Advisory Committee on Immunization Practices (ACIP).

Dr. Neuzil, whose expertise is in vaccine-preventable diseases, is a researcher with interests in epidemiological studies and clinical trials. She recently spoke with ACP Observer about this potentially fatal disease.

Q: Why is pertussis on the rise?

A: Part of the reason is thought to be waning immunity from the infant vaccine. Children before age seven get five doses of pertussis vaccine, but we don't give boosters in adolescence and adulthood. That's why we see a big surge in diagnoses in adolescents, about 10 years after they've received their last dose of vaccine. If they get the disease in adolescence, it may boost their immunity for a while, but they are still susceptible as adults.

Q: Are certain parts of the country more affected?

A: The CDC has noticed an across-the-board rise in cases generally, and in severe cases among infants. Massachusetts is one state that has brought the issue to the attention of the public, but that's because the state has a comprehensive surveillance program. In Seattle, there were more infant pertussis cases reported in 2003 than in any year since 1990.

Many adults don't know that they can get pertussis, and it's probably under-recognized by physicians. A number of studies have looked at adults with a severe cough illness that lasts two weeks or longer, and as many as 30% of adults in those studies have pertussis. It is a major, prolonged, severe coughing illness.

Q: What signs of pertussis distinguish it from other upper respiratory illnesses?

A: Pertussis has an incubation period of about seven days, and it can start with cold symptoms: watery eyes, runny nose and cough. The cough persists and becomes severe, lasting one to two months or more. The early illness can look like any other upper respiratory illness, so it is easy to miss early on when it's most contagious.

Pertussis causes coughing and gagging episodes that may end in vomiting and whooping. Children have the more classic presentation—a cough with a whooping sound—because they have smaller airways. These patients often don't have fever. Internists should consider pertussis in any adult who comes in with coughing episodes that end in vomiting, or who has a terrible cough but is fine between episodes.

Q: What steps should internists take with adults who may have pertussis?

A: Physicians have two options: test for the diagnosis or treat presumptively. Treatment of pertussis is most effective early on in the illness, but that's also when it's hardest to diagnose.

Available pertussis tests include direct fluorescent antibody, which is a rapid test, and pertussis cultures. Many health departments offer these tests, and internists should check there for local availability. If adult patients have contact with infants, it is even more important from a public health perspective to treat the patient presumptively. Polymerase chain reaction testing is becoming more widely available, and may be the test of choice in the future.

Q: What is the first line of treatment?

A: Pertussis has traditionally been treated with erythromycin, although there now are newer macrolides, such as azithromycin, that are more easily tolerated. Patients are considered to be contagious until they've received five days of antibiotics.

Q: Do you favor extending immunization to adults and adolescents?

A: It's a complex question and one the ACIP is considering now. If you took economics out of the issue, I'd like to see a comprehensive adult and adolescent program.

The question is, what's our goal? If the goal is to reduce adolescent pertussis, we should consider adolescent pertussis vaccine, which they administer in Canada.

If the goal is to reduce infant pertussis, that's much more difficult because many of those babies are partly immunized and develop the disease before they receive the full vaccine series.

To help infants, we would have to immunize the people who are spreading pertussis to them, such as adolescents and other adults in the household. If we want to have an impact on infant pertussis, we may have to consider maternal immunization or general immunization, not only in adolescents, but also every 10 years in adulthood. Pertussis immunization may also be important for health care workers, who have contact with susceptible persons.

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