Article Text

Original article
Emergence of parapneumonic empyema in the USA
  1. Carlos G Grijalva1,
  2. Yuwei Zhu2,
  3. J Pekka Nuorti3,
  4. Marie R Griffin1,4
  1. 1Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
  2. 2Department of Biostatistics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
  3. 3The National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
  4. 4Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
  1. Correspondence to Carlos G Grijalva, Department of Preventive Medicine, Vanderbilt University School of Medicine 1500 21st Avenue Suite 2600, The Village at Vanderbilt, Nashville, TN 37232-2637, USA; carlos.grijalva{at}


Background Although recent reports suggest that the incidence of parapneumonic empyema has increased in several regions of the USA, national trends in disease burden are unknown. National trends in the incidence of parapneumonic empyema hospitalisations and changes in empyema by associated pathogens were examined.

Methods National hospitalisation data (1996–2008) were analysed and rates estimated using census estimates as denominators. Incidence rate ratios (IRR) compared 2008 with 1996 rates. Discharge diagnosis codes were used to characterise pathogens associated with empyema hospitalisations.

Results Overall, national parapneumonic empyema-related hospitalisation rates increased from 3.04 per 100 000 in 1996 to 5.98 per 100 000 in 2008, a 2.0-fold increase (95% CI 1.8 to 2.1). The increases were observed among children (IRR 1.9 (95% CI 1.4 to 2.7)) and adults aged 18–39, 40–64 and ≥65 years (IRR 1.8 (95% CI 1.5 to 2.1), 2.0 (95% CI 1.6 to 3.1) and 1.7 (95% CI 1.5 to 2.0), respectively). Overall, pneumococcal empyema rates remained relatively stable in all age groups whereas streptococcal- (non-pneumococcal) and staphylococcal-related empyema rates increased 1.9-fold and 3.3-fold, respectively, with consistent increases across age groups. The overall in-hospital case fatality ratio for parapneumonic empyema-related hospitalisations was 8.0% (95% CI 6.4% to 9.5%) in 1996 and 7.2% (95% CI 6.3% to 8.1%) in 2008 (p=0.395). Of the empyemas where study pathogens were listed (37.6%), staphylococcal-related empyema had the largest absolute increases across age groups and was associated with longer hospital stay and higher in-hospital mortality than other empyemas.

Conclusions Although parapneumonic empyema-related hospitalisations remained relatively rare, they increased substantially during the study period. A number of pathogens, especially staphylococcus, contributed to this increase.

  • Bacterial infection
  • clinical epidemiology
  • empyema, pneumonia

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Supplementary materials

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  • See Editorial, p 649

  • Linked articles 161315, 157842.

  • Funding This study was funded by the Centers for Disease Control and Prevention through a Cooperative Agreement with the Association for Prevention Teaching and Research (TS-1454). CGG is supported by a CDC career development award (K01 CI000163).

  • Competing interests CGG received lecture fees from Wyeth (now Pfizer) and has been a consultant for GlaxoSmithKline. MRG received grant support from Med Immune. CGG and MRG received research support for an investigator-originated project from Wyeth (now Pfizer).

  • Ethics approval This study was considered exempt from review by the institutional review boards of Vanderbilt University and the Centers for Disease Control.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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