Impact of the pneumococcal conjugate vaccine on pneumococcal parapneumonic empyema

BACKGROUND: Pediatric pneumococcal parapneumonic empyema (PPE) has become increasingly common. In the last decade, Utah has had one of the highest rates of PPE in the United States, 14/100,000 children, attributed primarily to Streptococcus pneumoniae serotype 1. Our objective was to describe the temporal trends in PPE in Utah before and after the availability of the 7-valent pneumococcal conjugate vaccine (PCV-7). METHODS: The Intermountain Health Care (IHC) data warehouse was queried for all cases of empyema in children younger than 18 years, defined as International Classification of Diseases, 9th revision, Clinical Modification code 510.9, for the study period March 1996-June 2005. We also retrieved and serotyped all blood and pleural fluid isolates of S. pneumoniae from children younger than 18 years with a diagnosis of PPE at Primary Children's Medical Center (PCMC) between March 1996 and June 2005. The pre-PCV-7 period (PRE) included 57 months (March 1996-December 2000) and the post-PCV-7 period (POST) included 54 months (January 2001-June 2005). RESULTS: We identified 776 cases of pediatric empyema in the IHC system, and 478 (62%) were managed at PCMC. In the years 1996-2000, we managed a mean of 38 cases of empyema per year compared with 71.5 cases per year between 2001 and 2004 (P = 0.006). At PCMC, there were 295 cases of invasive pneumococcal disease (IPD), and 74 (25%) were PPE. During the PRE period, PPE represented 24 of 137 (17.5%) cases of IPD compared with 50 of 158 (32%) in the POST period (P = 0.008). One-half of the children with PPE required intensive care and 4 died. During the PRE and POST periods, PPE was most often caused by serotype 1 (46 and 34%, respectively), but in the POST period serogroups 3 (20%), and 19A (14%) were also prevalent. PPE in PCV-7-immunized children was caused exclusively by nonvaccine serotypes. CONCLUSIONS: PPE in the post-PCV-7 era is more common, representing one-third of the IPD in children in UT. PPE is associated with significant morbidity and mortality. Serotype 1 remains the most common cause of PPE, but serotypes 3 and 19A are emerging.