Incidence of Invasive Pneumococcal Disease among Individuals with Sickle Cell Disease before and after the Introduction of the Pneumococcal Conjugate Vaccine

Abstract

We sought to determine the incidence of invasive pneumococcal disease (IPD) among individuals with sickle cell disease (SCD) before and after the introduction of the pneumococcal conjugate vaccine (PCV). Individuals with SCD who were enrolled in Tennessee Medicaid from January 1995 through December 2004 were identified using SCD-specific International Classification of Diseases, Ninth Revision, Clinical Modification codes. Population-based surveillance data were used to identify individuals with IPD and were linked to patients with SCD in the Tennessee Medicaid database to determine incidence rates of IPD. Clinical data were collected on all subjects with IPD, and antibiotic susceptibility testing and serotyping were performed on all available pneumococcal isolates. We identified 2026 individuals with SCD, who constituted 13,687 person-years of follow-up. During the study period, 37 individuals with SCD developed IPD, and 21 of these patients were aged <5 years. In a comparison of the pre-PCV period (1995-1999) with the post-PCV period (2001-2004), the rate of IPD decreased by 90.8% in children aged <2 years (from 3630 to 335 cases per 100,000 person-years; P<.001) and by 93.4% in children aged <5 years (from 2044 to 134 cases per 100,000 person-years; P<.001). Rates of IPD for patients with SCD who were aged >or=5 years decreased from 161 cases per 100,000 person-years during the pre-PCV period to 99 cases per 100,000 person-years during the post-PCV period (P=.36). The rate of IPD among children with SCD who are aged <5 years has decreased markedly since the introduction of routine administration of PCV to young children.