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Background: Pertussis is an acute respiratory illness caused by the bacterium Bordetella pertussis that is characterized by prolonged and severe cough. California is experiencing its highest rates of pertussis reported in over 50 years.
Objectives: Understand the epidemiology of pertussis in the 2010 California epidemic.
Methods: Pertussis cases in California are reportable to local public health departments, which collect information on case demographics, clinical presentation and risk factors.
Results: 6,795 cases of pertussis, including 282 hospitalizations and 10 fatalities, with onset in 2010 were reported in California for an incidence of 17.4 cases/100,000. The majority (77%) were <18 years of age. Incidence by age-group is highest among infants <6 months (345.7 cases/100,000) followed by children and adolescents aged 7-10 years (61.7/100,000). Rates are highest in Hispanics (17.9/100,000) and whites (14.7/100,000), compared to blacks (7.1/100,000) and APIs (4.2/100,000). Among infants <6 months of age, 73% were Hispanic (426.4 cases/100,000); among those aged 7-18 years, the highest incidence was in whites (55.4/100,000). Of 1,215 cases aged 6 months to 18 years with vaccination information, 13% were unimmunized against pertussis, 34% were up-to-date and 53% were missing >1 recommended dose; 63% of these were aged 11-18 years and had not received a Tdap booster dose.
Conclusions: Young infants are at highest risk of severe pertussis and should therefore be prioritized for prevention efforts (“cocooning”), early diagnosis and treatment. Low Tdap coverage, imperfect vaccine efficacy and waning immunity contribute to sustained transmission of pertussis in the United States. The number of cases occurring in children aged 7-10 years is concerning since children in this age group may have contact with infant siblings; most in this age group were fully immunized (5 DTaPs) indicating they are at risk of disease due to primary vaccine failure or waning immunity.