Prospective pertussis surveillance in Switzerland, 1991–2006

Abstract

Pertussis has been monitored in Switzerland since 1991 by the nationwide Swiss Sentinel Surveillance Network (SSSN), consisting of approximately 200 general practitioners, internists and pediatricians representing about 3% of the total primary care physicians of these specialities. SSSN members report patients with cough ≥14 days plus either an epidemiological link or characteristic symptoms (paroxysms, whoop, post-tussive vomiting) on a weekly basis to the Federal Office of Public Health. Confirmatory PCR from nasopharyngeal specimens is offered for free. A total of 4992 cases have been reported until 2006. Yearly incidence has dropped from 70 cases per 100,000 inhabitants in 1992 to 40 in 2006, with a single epidemic in 1994–1995 with 280–370 cases/100,000. On average 80% of reported cases were tested by PCR, 24% of these were confirmed as Bordetella pertussis infections. For 2.6% of patients complications were reported, most commonly pneumonia, asthma bronchiale, otitis media, bronchitis and rib fractures. On average, 1.5% of patients were hospitalized. Disease in vaccinated patients was mitigated with less frequent complications (unvaccinated: 5.1%; 3 doses: 3.0%; ≥4 doses: 1.7%), hospitalizations (unvaccinated: 3.6%; ≥1 dose: 1.1%) and various clinical symptoms compared to unvaccinated patients. Comparing the periods 1991–1996, 1997–2001 and 2002–2006, a shift of pertussis from age group 1–9 years to 10–19 and ≥40 years was observed among patients cared for by general practitioners and internists. The benefits of further booster doses in adolescents and/or adults need to be considered.