Epidemiology of invasive pneumococcal disease in Southern California: Implications for the design and conduct of a pneumococcal conjugate vaccine efficacy trial

Population-based prospective surveillance of invasive pneumococcal disease was done in Southern California from 31 March 1992 to 1 April 1995; 814 cases were identified for an incidence of 12.5/100,000 persons/year. The incidence among persons ≤2, ≤5, and ≤65 years of age was 145, 72, and 32/100,000, respectively. More than 95% of cases included bacteremia: incidence of meningitis was 0.8/100,000. Among children ≤2 years of age, 79% of isolates were obtained in the outpatient setting, compared with 16% of isolates among persons ≤15 years of age. Eighty percent of isolates were serotypes included in heptavalent pneumococcal conjugate vaccines currently being evaluated. Children ≤2 years of age were at highest risk of having an isolate resistant to penicillin. Among resistant isolates, high-level resistance increased from 4% to 21% over a 3-year period. Prospective epidemiologic data are needed to perform a protective efficacy trial of pneumococcal conjugate vaccines in infants, among whom most invasive pneumococcal disease is vaccine-preventable.