Original Papers

Influenza and respiratory tract infections

Seasonal patterns in time series of pertussis

S. C. De GREEFF^a1 c1, A. L. M. DEKKERS^a2, P. TEUNIS^a1a3, J. C. RAHAMAT-LANGENDOEN^a1, F. R. MOOI^a4 and H. E. De MELKER^a1

^a1 Epidemiology and Surveillance, Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands

^a2 Expertise Centre for Methodology and Information Services, National Institute for Public Health and the Environment, Bilthoven, The Netherlands

^a3 Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA

^a4 Laboratory for Infectious Diseases and Screening, National Institute for Public Health and the Environment, Bilthoven, The Netherlands

SUMMARY

To gain insight into pertussis disease dynamics, we studied age-specific long-term periodicity and seasonality of pertussis in The Netherlands. Hierarchical time-series models were used to analyse the monthly reported pertussis incidence in January 1996–June 2006 by age group. The incidence of pertussis showed a slightly increasing long-term trend with highest incidence rates seen in 1996, 1999, 2001 and 2004. For all age groups the annual peak incidence was found in August, except for the 13–18 years age group where the peak occurred in November. Monthly trends in adults showed high correlation with trends in age groups 0–4 years (0·94) and 5–12 years (0·92). We found no evidence for a relationship between annual rises in pertussis and the opening of schools. Concurrent annual fluctuations of pertussis incidence in adults and infants suggest frequent transmission within and between these age groups. Studying trends offers insight into transmission dynamics and may facilitate decisions on future vaccination strategies.

(Accepted February 23 2009)

(Online publication March 30 2009)

Key Words:

• Pertussis;
• seasonality;
• vaccination strategies

Correspondence:

^c1 Author for correspondence: S. C. de Greeff, National Institute of Public Health and the Environment, PO Box 1, 3720 BA Bilthoven, The Netherlands. (Email: sabine.de.greeff@rivm.nl)