When pertussis is not whooping cough.

Pediatric textbooks traditionally liken pertussis to rubella, in that a single bout of infection or a vaccination against the microbe responsible is thought to confer lifetime immunity. A spate of new studies, however, indicates that pertussis can strike repeatedly throughout life; it just remains largely misdiagnosed because few victims apart from infants develop the signature whooping cough.

Two of these new studies took place in Germany, where until recently physicians did not routinely vaccinate children against the disease.

In the most recent study, Carl Heinz Wirsing von Koenig of the municipal Institute for Hygiene and Laboratory Medicine in Krefeld and his coworkers monitored the spread of pertussis in househods after the diagnosis of a case. In the Nov. 18 Lancet, they report that 55 percent of exposed children developed the highly infectious disease, as did 27 percent of exposed adults. Moreover, at least one-third of the 80 symptomatic adults recalled having had pertussis 20 or more years earlier.

To diagnose the disease in adults, the researchers tested for high concentrations of pertussis antibodies in individuals whose cough lasted at least 6 days. Compared to children, adults exhibited fewer episodes of prolonged coughing, vomiting, or whooping but proved more likely to develop headaches, sinus pain, and attacks of sneezing, sweating, or choking.

A second team also found high rates of adult pertussis in Germany, this time during a 3.5-year-long study of 900 households where children were vaccinated. Again, generally relying on antibody counts or the polymerase chain reaction (to identify DNA from the pertussis bacterium), researchers diagnosed the disease in 32 percent of adults who had a cough that had lasted more than 2 weeks. James D. Cherry of the University of California, Los Angeles School of Medicine and his coworkers describe their findings in the October Clinical Infectious Diseases.

Three years ago, Cherry's group identified similar rates of pertussis-26 percent in a 30-month-long study-among UCLA students going to the school health service with complaints of a cough lasting at least 6 days. Unlike the German adults, most of these students had been vaccinated.

In this month's Clinical Infectious Diseases, his group reports on 255 Californians exposed to pertussis at home. They diagnosed infection in 46 percent of patients with no symptoms, in 43 percent of those with mild respiratory illness, and in 80 percent of individuals, mostly infants less than 6 months old, exhibiting the classic whooping cough. The disease tends to be lethal only in this youngest group.

Cherry's data suggest that by age 20 everyone, even in the United States, has developed infectious pertussis. But he suspects that by initiating booster immunizations for adults-perhaps at age 15 and every 10 years thereafter-"you should decrease the major source of infection during the first year of life, which is parents."