Study finds very low rates of pertussis in children with cough

Contrary to some recent studies, only a low percentage of children treated for respiratory illness with cough have unsuspected pertussis, reports a study in the August issue of The Pediatric Infectious Disease Journal. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

Although some children with respiratory viral illnesses are also infected with the Bordetella bacteria that cause pertussis, the most likely explanation is coincidence—rather than any predisposition to secondary infection. The study was performed by Drs. Ulrich Heininger and Marie-Anne Burckhardt of University Children's Hospital, Basel, Switzerland.

Very Low Rates of Pertussis in Children with Cough
The researchers analyzed nasopharyngeal (nose and throat) swabs from 1,059 infants, children, and adolescents with cough illness treated over a one-year period. In addition to respiratory viruses, the swabs were tested for Bordetella bacteria, including Bordetella pertussis—the main cause of pertussis. They were also tested for a related species, Bordetella parapertussis, which can also cause pertussis.

In addition, the researchers looked at how often children with common respiratory viruses had concurrent infection with Bordetella bacteria. Some recent studies have suggested that many children with cough related to common viral infections may also have unsuspected Bordetella infection.

The tests showed low rates of Bordetella infection: 2.0 percent for B. pertussis and 0.5 percent for B. parapertussis. The rates were low even for children whose doctor ordered a test for Bordetella to check for possible pertussis.

Rates of Bordetella infection were also low in children with confirmed respiratory viral infections. Of 268 patients who tested positive for respiratory syncytial virus (RSV)—a very common respiratory infection in infants—just one was also infected with Bordetella.

Pertussis is a serious, highly communicable childhood disease. It has the descriptive name "whooping cough" because it causes a distinctive-sound, uncontrollable cough. Although routine vaccination is effective, outbreaks of pertussis still occur.

The new findings help reassure doctors that they aren't overlooking unsuspected cases of pertussis in infants and children with cough illness—the vast majority of which are caused by RSV or other viruses.

The study also provides no evidence that infection with respiratory viruses makes children more vulnerable to Bordetella infection. When the infections occur together, it's most likely a coincidence, rather than any special susceptibility, Dr. Burckhardt and colleagues believe.

At the same time, they emphasize that detecting RSV or other respiratory viruses doesn't ensure that the child isn't also infected Bordetella. They also acknowledge some important limitations of their study—including the fact that it was carried out in a single year during which there were no pertussis outbreaks.