Reduction in High Rates of Antibiotic-Nonsusceptible Invasive Pneumococcal Disease in Tennessee after Introduction of the Pneumococcal Conjugate Vaccine

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Abstract
Background. Invasive pneumococcal disease (IPD) is a burgeoning problem, with rates of antibiotic-nonsusceptible IPD, in particular, increasing during the past decade. One measure to combat IPD is vaccination with the recently introduced 7-valent pneumococcal conjugate vaccine (PCV). Methods. To evaluate the effects of the introduction of PCV in 2000 on the epidemiology of antibiotic-nonsusceptible IPD, a database of IPD cases from January 1995 through December 2002 identified through active surveillance in 5 Tennessee counties was examined. For each case, clinical data were collected, and antibiotic susceptibility testing and serotyping were performed on available isolates. Results. Among children younger than 2 years, IPD rates peaked at 235 cases per 100,000 in 1999 before decreasing, after PCV licensure, to 46 cases per 100,000 in 2002 (P < .001). The proportion of penicillin-nonsusceptible IPD isolates from this age group declined from 59.8% in 1999 to 30.4% in 2002 (P < .01). After 2001, similar decreases in IPD rates and in the proportion of antibiotic-nonsusceptible isolates recovered were seen among persons aged 2 years and older (P < .01). Rates of IPD due to PCV-associated serotypes declined after PCV introduction in all age groups (P < .001), whereas the rate of IPD due to nonvaccine serotypes increased among persons aged 2 years and older. Conclusions. In the 2 years since licensure, widespread PCV vaccination of children has resulted in dramatic declines in the proportion of antibiotic-nonsusceptible isolates in Tennessee. PCV vaccination of children also appears to be a highly effective method for reducing the burden of IPD in adults.