The Centers for Disease Control and Prevention describe whooping cough as a highly communicable disease that lasts for many weeks. It is typically manifested in children with paroxysmal spasms of coughing, with the characteristic "whoop" as they try to catch their breath. In the youngest infants, there may also be gagging, vomiting, apnea and sneezing.

"If you're unvaccinated, you're more likely to have a classic illness, with the whoop. But even vaccinated kids might just have a mild cough," said Dr. Margaret Cortese of the CDC. And infants might not whoop because they are not strong enough to generate the pressure to make one.

Why is diagnosis and testing of pertussis so problematic?

"One reason is that adults and adolescents tend to go to the doctor a little later," said Cortese. After three weeks, the coughing may be persisting but the bacteria is no longer in the system. A standardized test would help identify the illness and prevent other testing that may be considered when trying to determine the cause of the prolonged cough.

The bacteria itself, Bordetella pertussis, is, as Dr. Michael Decker of Aventis Pasteur describes "very delicate outside the body.

Samples for what's called a PCR test are usually taken by inserting a swab into the back of the nose and even if you get the bug to the lab right away, the regular culture media won't grow it, he said.

There are blood tests, but "they pretty much work only in a study because they rely on having a pre-illness blood test" for comparison.

For more information

A web site, www.pertussis.com, is an educational project of the National Association of Pediatric Nurse practitioners and has video and audio of a child in the throes of whooping cough, plus a map of outbreaks and other information.

To read the CDC's technical information sheet on pertussis online, visit www.cdc.gov, click on the Emerging Infectious Diseases bar on the left, and at that page click on the Disease Information bar, also on the left.

Bordetella pertussis is a member of the same genus as Bordetella bronchiseptica, which causes kennel cough in dogs.

-- Katy Buchanan