Background. The California Department of Public Health (CDPH) declared a pertussis epidemic on 23 June 2010. More cases were reported in 2010 (9146) than in any year since 1947. We describe the characteristics of pertussis epidemiology and disease from 986 reported cases in children in San Diego County (population 3.2 million).
Methods. Descriptive statistics were abstracted from CDPH pertussis case report forms that were completed by public health nurses investigating reports of positive laboratory results for pertussis and reports of illnesses compatible with pertussis.
Results. Of 1144 reported adult and pediatric cases, 753 (66%) were confirmed and 391 were probable/suspect. Children aged <19 years comprised 86% of all reported cases in San Diego County; of these, 22% were aged 11–18 years, 29% were aged 6–10 years, 27% were aged 1–5 years, and 22% were aged <1 year (with 70% aged <6 months). Case rates were highest in infants aged <6 months (651 per 100 000 population). Of those aged >1 year, the highest attack rates were in preschool children aged 1–5 years (114 per 100 000) and elementary school children aged 6–10 years (141 per 100 000). Of 51 children hospitalized, 82% were aged <6 months; 2 deaths occurred in these young infants. Paroxysmal cough was noted in over 70% of children in all age groups; post-tussive vomiting occurred in 36% (aged 11–18 years) to 57% (aged <6 months) of children.
Conclusions. Pertussis vaccine efficacy may decrease more rapidly than previously believed, facilitating spread of pertussis in elementary school–aged children. The highest case rates and the only mortality occurred in infants aged <6 months.
Journal: J Ped Infect Dis Soc, 2013