Incidence trends in pertussis in the Autonomous Region of Madrid, Spain: 1982-2005.

The objective of this study was to describe the incidence (1982-2005) and epidemiologic characteristics of pertussis cases (1998-2005) in the Autonomous Region of Madrid using data drawn from the epidemiologic surveillance network and computerised hospital discharge data. In the 1990s, the trend in the pertussis incidence in the Autonomous Region of Madrid was clearly falling. The typical seasonal pattern of pertussis remained. A peak in incidence were observed in 2000, and another peak, 2.5 times higher, in 2003. They affected all age groups, but children under one year of age were the most frequent cases, followed by the five to nine year-olds. The greatest increase was seen in the age groups from 10 to 14 and from five to nine. Since 2002, the proportion of cases diagnosed serologically has increased. The incidence of hospital discharges among small children exceeded that of reported cases. More than half of the cases with known vaccination status had received at least three doses of vaccine. The upward trend observed since 2002 could be due to improved case detection, availability of serologic techniques, and a rise in the susceptible population aged five to 14 years. The fact that epidemic peaks continue to occur and that there is a seasonality to the disease seems to indicate that despite the vaccination programme the circulation of the bacteria has not been interrupted. The introduction of the acellular vaccine in 2000 does not appear to have played a significant role in the increase in disease incidence.