California pertussis epidemic, 2010.

OBJECTIVE: In 2010, California experienced the highest number of pertussis cases in >60 years, with >9000 cases, 809 hospitalizations, and 10 deaths. This report provides a descriptive epidemiologic analysis of this epidemic and describes public health mitigation strategies that were used, including expanded pertussis vaccine recommendations.

STUDY DESIGN: Clinical and demographic information were evaluated for all pertussis cases with onset from January 1, 2010, through December 31, 2010, and reported to the California Department of Public Health.

RESULTS: Hispanic infants younger than 6 months had the highest disease rates; all deaths and most hospitalizations occurred in infants younger than 3 months. Most pediatric cases were vaccinated according to national recommendations, although 9% of those aged 6 months to 18 years were completely unvaccinated against pertussis. High disease rates also were observed in fully vaccinated preadolescents, especially 10-year-olds. Mitigation strategies included expanded tetanus, diphtheria, and acellular pertussis vaccine recommendations, public and provider education, distribution of free vaccine for postpartum women and contacts of infants, and clinical guidance on diagnosis and treatment of pertussis in young infants.

CONCLUSIONS: Infants too young to be fully vaccinated against pertussis remain at highest risk of severe disease and death. Data are needed to evaluate strategies offering direct protection of this vulnerable population, such as immunization of pregnant women and of newborns. The high rate of disease among preadolescents suggests waning of immunity from the diphtheria, tetanus, and acellular pertussis series; additional studies are warranted to evaluate the efficacy and duration of protection of the diphtheria, tetanus, and acellular pertussis series and the tetanus, diphtheria, and acellular pertussis series.