AJM Theme Issue: Pulmonology/Allergy
Clinical research study
Thoracic Empyema in Patients with Community-Acquired Pneumonia

https://doi.org/10.1016/j.amjmed.2006.03.042Get rights and content

Abstract

Purpose

The objective of this study was to update the incidence and natural history of empyema in patients admitted to hospital with community-acquired pneumonia (CAP).

Methods

A prospective population-based study of 3675 patients with a diagnosis of CAP was carried out. Patients were classified as “definite empyema” based on one or more of the following criteria: presence of microorganisms in pleural fluid Gram stain or culture, pleural pH less than 7.2 associated with radiographic features of empyema, or frank pus in the pleural space at the time of thoroscopy. All others were classified as either “suspected empyema” or CAP. We then compared characteristics and outcomes between subgroups.

Results

A diagnosis of empyema was made in 47 patients (1.3%) by the attending physician; 24 patients (0.7%) met criteria for definite cases. Few clinical, laboratory, or radiographic features were useful in differentiating patients with definite empyema. The most commonly isolated pathogen from pleural fluid of patients with definite empyema was Streptococcus milleri group (50%). The in-hospital mortality rate for patients with definite empyema was 4.2%.

Conclusion

In the 21st century, empyema is an uncommon complication of CAP with an incidence of 0.7%. The S. milleri group has emerged as the most common causative microbial pathogen. The diagnosis remains difficult, although outcomes have improved from that previously reported.

Section snippets

Subjects

All patients admitted to a hospital within the Capital Health region (Edmonton, Canada) with a clinical diagnosis of CAP between November 15, 2000, and November 14, 2002, were included in the study population. Capital Health region is an integrated health system that serves a population of approximately 1 million people and is composed of 2 tertiary care hospitals, 2 hospitals that provide secondary and some tertiary care, 2 community hospitals, and 1 freestanding emergency department. This

Results

Over a 2-year period, 3675 patients were admitted to Capital Health region with suspected CAP. Of these, 47 (1.3%) patients were given a diagnosis of empyema by the attending physician. After our definition of empyema was applied to this subgroup, 24 (0.7%) were definite cases, and 23 (0.6%) were classified as suspected cases of empyema (Figure 1).

Discussion

The true incidence of thoracic empyema complicating CAP has not been well defined and was previously noted to be 1.6%10 In our study, 1.3% of patients admitted to a hospital with a clinical diagnosis of CAP were diagnosed with empyema by the attending physician. Of these, only half (24/47 patients) actually met conventional microbiologic, pleural fluid, or radiologic criteria for the diagnosis, giving a true incidence of 0.7%. The remaining patients had complicated pleural effusion and not true

Conclusion

This study shows several important updated features of empyema caused by CAP. First, empyema seems to be an uncommon complication of CAP with an incidence of 0.7%. Clinical and laboratory features remain nonspecific and should be used with caution when differentiating among empyema, complicated parapneumonic effusion, and CAP. This study is also consistent with the trend of S. milleri group as an emerging pathogen in the pathogenesis of empyema. Finally, in-hospital mortality seems to be

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