Nearly 40 per cent of school-age children in Britain who go tothe doctor with a persistent cough have signs of whooping cough infection, even though most were immunized, researchers found.

Whooping cough, also known as pertussis, is easily spread by coughing or sneezing. It gradually worsens to violent coughing spells that have a distinctive gasping or whooping sound, particularly in infants.

The results suggest whooping cough is endemic among school-age children in the U.K. But family doctors seldom diagnose or consider the infection for that age group, because the symptoms may not be as clear, the team said.

"Whooping cough is perceived as a disease of very young children who have not been immunized and who have classic features such as whoop," Anthony Harnden of Oxford University and his colleagues wrote in Friday's online issue of the British Medical Journal.

International studiesshowed whooping cough is endemic among teens and adults with a persistent cough, and thatimmunization and infection don't offer lifelong protection against whooping cough.

Harnden's team studied 172 children aged five to 16 who visited their family doctor with a cough lasting at least two weeks.

Immunization records were checked, symptoms noted and blood samples taken to test for Bordetella pertussis, the bacteria that cause whooping cough.

Of these, 64 or 37 per cent showed signs of whooping cough infection, although nearly 86 per cent were immunized against the bacterial infection.

Children with whooping cough were more likely than others to demonstrate:

  • Whooping.
  • Vomiting.
  • Sputum production.
  • A cough lasting two months.
  • More than five coughing episodes a day.
  • Disruption oftheir parents' sleep.

Given the results, the team urges family doctors to be aware of the potential diagnosis of whooping cough in children with a persistent cough.

If doctors secure a diagnosis, they can tell parents how long the cough could likely last, and thereby prevent unnecessary prescriptions for asthma or referrals.