An epidemic of pertussis among elderly people in a religious institution in The Netherlands

An epidemic of pertussis is described among elderly people in a religious institution in the Netherlands in 1992. Subjects were evaluated for their vaccination status and for history and presence of respiratory symptoms. Specimens were collected for culture, polymerase chain reaction, and serological evaluation. None of the 75 residents and 19 of 24 nonresident personnel had been vaccinated against pertussis. The overall attack rate of clinical pertussis, defined as persistent cough lasting at least 2 weeks, was 49%. In five subjects with clinical pertussis, either culture or polymerase chain reaction or both were positive for Bordetella pertussis. A significant (at least 4-fold) change in specific antibody titre was observed in 85% (41/48) and 20% (10/49) of subjects with and without clinical pertussis, respectively (P < 0.0001, chi-square 41.1). The attack rate of laboratory-confirmed pertussis was 42% (41/98). This rate was 5% (1/19), 20% (1/5), and 53% (39/74) in vaccinated personnel, nonvaccinated personnel, and nonvaccinated residents, respectively (not significant). Among residents aged between 55-74 years and 75-94 years, the attack rates were 47% (17/36) and 58% (22/38), respectively (relative risk=0.8; 95% confidence interval 0.5-1.3). Four of 75 residents (5%) died from intracranial bleeding, while they were symptomatic for pertussis. It is concluded that the attack rate of pertussis was high among nonvaccinated elderly and that pertussis tended to increase with age. There may be a considerable risk of mortality from pertussis in this population. Physicians should be alert to the diagnosis of pertussis in the elderly with nocturnal and prolonged periods of coughing.