Characteristics of pertussis outbreaks in Catalonia, Spain, 1997 to 2010

Abstract

In Catalonia, pertussis outbreaks must be reported to the Department of Health. This study analyzed pertussis outbreaks between 1997 and 2010 in general and according to the characteristics of the index cases. The outbreak rate, hospitalization rate and incidence of associated cases and their 95%CI were calculated. Index cases were classified in two groups according to age (<15 years and ≥15 years) and the vaccine type received: whole cell vaccine (DTwP) or acellular vaccine (DTaP). During the study period, 230 outbreaks were reported. The outbreak rate was 2.43 × 10⁻⁶ persons-year, and outbreaks ranged from 2 to 32 cases, with a median duration of 18 days. There were 771 associated cases, with an incidence rate of 0.8 × 10⁻⁵ persons-year.

 

After classifying outbreaks according to the age of the index case, 126 outbreaks (1.3 × 10⁻⁶ persons-year) had an index case aged <15 y and 87 (0.87 × 10⁻⁶ person-year) had an index case aged ≥15 y (RR = 1.44, 95%CI 1.10–1.90; P = 0.007).

Between 2003 and 2010, after the introduction of the acellular vaccine, the index case was vaccinated with DTwP vaccine in 25 outbreaks (0.43 × 10⁻⁶ persons-year) and with DTaP vaccine in 32 outbreaks (0.55 × 10⁻⁶ person-year) (RR = 0.78, 95%CI 0.46–1.31; P = 0.35).

Of cases, 37.2% were correctly vaccinated, suggesting waning immunity of pertussis vaccine protection and endogenous circulation of pertussis. A greater number of outbreaks had an index case aged <15 y. No changes in the disease incidence, associated cases and hospitalization rate were observed after the introduction of DTaP.

Keywords: :

• pertussis
• hospitalization
• surveillance
• whole cell pertussis vaccine
• acellular pertussis vaccine

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgements

The authors thank the other members of the Pertussis Surveillance Group of Catalonia, Pedro Plans, Glòria Carmona, Yolanda Jordan, Irene Barrabeig, César Arias, Mònica Carol, Neus Camps, Miquel Alsedà, and José Álvarez, and reporting physicians and staff of the epidemiological surveillance units who participated in the notification of cases and in collecting vaccination histories.

Funding

This study was partially funded by CIBER Epidemiología y Salud Pública (CIBERESP), and AGAUR (expedient 2009 SGR 42).