Pertussis: A Highly Contagious Disease Raises Its Ugly Head in Adults

Pertussis: A Highly Contagious Disease Raises Its Ugly Head in Adults

CDC Issues New Adult Vaccination Recommendations

By Rebekah McCallister

The rising rate of pertussis, or whooping cough, cases in adults and adolescents has come as a shock to health care professionals and patients alike—so much so that the infection is being misdiagnosed in many adults, opening the door to the transmission of infection to unprotected infants in whom this illness can be life threatening.

As a result, the Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices has issued new recommendations that adults receive 1 of 2 recently approved tetanus-diphtheria-acellular pertussis boosters (Adacel, Sanofi Aventis;Boostrix, GlaxoSmithKline) instead of the previously recommended tetanus-diphtheria (Decavac) booster.

The approved indications for these vaccines are slightly different from the new recommendations. Boostrix, which is not recommended for the treatment of actual infection, is indicated for active booster immunization against tetanus, diphtheria, and pertussis as a single dose in patients aged 10 through 18 years. The use of Boostrix as a primary series or to complete the primary series has not been studied. Adacel, approved in June 2005, is indicated as a booster immunization against tetanus, diphtheria, and pertussis as a single dose in individuals aged 11 to 64 years.

The new recommendations were highlighted during a recent CDC teleconference, during which CDC epidemiologist Katrina Kretsinger, MD, lieutenant commander of the US Public Health Services, pointed out that immunity derived from childhood vaccination against pertussis begins to wane after about 5 to 10 years.

Dr Kretsinger noted that pertussis is typically thought of as a childhood disease, and many physicians “may not be aware that pertussis can cause serious illness in adults. They may not think about pertussis at all, even when an adult has very typical classic pertussis, including a whoop after the cough.”

In 2004, almost 26,000 cases of pertussis were reported to the CDC, according to Dr Kretsinger, with 7000 of these occurring in adults 19 to 64 years of age—an increase of 150% from 2003. This number is believed to represent only a small fraction of the cases that actually occur, she noted. “For every case of pertussis in adults that is reported to the CDC, there are almost 100 additional cases that are not reported.”

Speaking firsthand about how easy it can be to miss the signs of pertussis was Russell Steel, MD, of Children’s Hospital and Louisiana State University School of Medicine, both in New Orleans, who told of an experience 3 years earlier. He was working in a vaccine clinic where a nurse developed a chronic cough that persisted for several weeks. Eventually the cough became so violent that she had to be rushed to the emergency department, where she was diagnosed with pertussis. “Now, that cough had gone on for weeks,” he said. “Here I was in the clinic and didn’t recognize the diagnosis. Obviously, she was exposing other young children.”

Dr Steel described an outbreak of pertussis in Louisiana this past spring, which resulted in the deaths of 2 young children. “It was quite clear that both of these infants were exposed by their mothers,” he said.

Pertussis, which is caused by bacteria found in the mouth, nose, and throat, spreads through close contact. Adults may experience symptoms such as prolonged coughing, which is sometimes so severe that it causes vomiting. Adults with severe cases may develop pneumonia and need to be hospitalized. “Because pertussis is a highly contagious disease, about 90% of people susceptible in a household will pick up pertussis if you have 1 case in a household,” Dr Steel noted.

The efficacy of GlaxoSmithKline’s booster vaccine was recently tested in a study published in the New England Journal of Medicine (2005;353:1555-1563), which showed the acellular vaccine was protective in adults and adolescents.

This national, multicenter, double-blind study included 2781 healthy participants (aged 15-66 years) who were randomized to receive a dose of a tricomponent acellular pertussis vaccine (n = 1391) or a hepatitis A vaccine (n = 1390) and were followed for approximately 2.5 years for illnesses with cough that lasted >5 days. Nasopharyngeal aspirate for culture and polymerase chain reaction assay were used to evaluate illnesses, and serum samples from patients in both acute and convalescent stages of illness were studied for alterations in antibodies to 9 Bordetella pertussis antigens.

A total of 2672 prolonged illnesses with cough were documented among both groups, but incidence did not differ between groups, even when age, season, and duration of cough were taken into account. In the treatment group, the vaccine showed 92% protection against pertussis according to the case definition. In the control group, 0.7% to 5.7% of participants were found to have B pertussis infection, and the percentage was higher with the duration of cough.

Lead investigator Joel I. Ward, of the UCLA Center for Vaccine Research, Research and Education Institute, Harbor-UCLA Medical Center, David Geffen School of Medicine, UCLA, Torrance, Calif, and colleagues noted the similarities between the 2 vaccines and recommended their use in adolescent and adult populations.

“Although the vaccines differ slightly in formulation, they are thought to have equivalent safety, immunogenicity, and protective efficacy,” they wrote. “Data suggest that both of the newly licensed acellular pertussis vaccines will be efficacious among adolescents and adults.”

The first CDC recommendation, that all adults should receive a single dose of the new vaccine, is designed to protect adults, according to Dr Kretsinger. “This should occur whenever a given adult is next due for a tetanus booster,” she said. “This raises the question: Does an adult need to wait until they need their next tetanus booster to get their pertussis vaccine? The answer is no.”

The second recommendation is designed to protect infants and states that all adults in close contact with infants <12 months of age or who anticipate having contact with infants <12 months of age should receive the booster vaccine. “Women of childbearing age who become pregnant are encouraged to receive the new pertussis booster to protect the woman from pertussis, and in case they become pregnant, to protect the baby,” Dr Kretsinger said.

Adult groups that are not included in the recommendations include health care workers in general, pregnant women, and adults aged ≤65 years, she noted.

Susan J. Rehm, MD, of the National Foundation for Infectious Diseases and medical director at the Cleveland Clinic, commented, “One of the things that we lack in the United States is a…well-known and regulated schedule for adults to receive vaccination. We have a big job ahead of us as health care providers and educators to let people know about what vaccines are recommended and at what intervals.”