J Porcel, P Vázquez, M Vives, A Nogués, M Falguera, A Manonelles
empyema, pleural effusion, pneumonia
J Porcel, P Vázquez, M Vives, A Nogués, M Falguera, A Manonelles. Pleural Space Infections: Microbiologic And Fluid Characteristics In 84 Patients. The Internet Journal of Pulmonary Medicine. 2002 Volume 3 Number 1.
Parapneumonic effusions and empyema are a common clinical problem without a good variety of treatment options, occasionally having poor outcomes. Empyema is usually a complication of pneumonia but may arise from infections at other sites. The microbial etiology of pleural space infections has changed since the introduction of antibiotics, and is modified by either specific patient factors such as surgical procedures, trauma or underlying conditions, or by methodological factors, namely the proper specimen collection, transport and culture. For these reasons, several studies have found discordant results in the spectrum of pathogens causing pleural infections1. We reviewed our experience with the microbial causes of pleural empyema over a 10-year period at a University hospital. In addition, we sought to ascertain the biochemical characteristics of these fluids and whether all culture positive effusions need drainage.
Patients and Methods
The medical records of all patients who had a positive culture of pleural fluid at University Hospital Arnau de Vilanova, a 470-bed teaching hospital in Lleida, during the period of January 1992 through December 2001, were reviewed. We excluded cases of tuberculous pleuritis.
A parapneumonic effusion was diagnosed in patients with an effusion associated with a pulmonary infiltrate, and clinical signs of infection (fever, leukocytosis). Typical or non-complicated parapneumonic effusions received appropriate antibiotics alone. Complicated parapneumonic effusion referred to those nonpurulent-appearing effusions that did not resolve without tube thoracostomy, whereas empyema described pus within the pleural space, the end stage of a complicated effusion.
All patients underwent diagnostic thoracentesis under aseptic conditions, and the pleural fluid was processed for measurement of pH, glucose, protein, lactate dehydrogenase, adenosine deaminase (ADA), cell count and differential, cytology, and both aerobic and anaerobic bacterial cultures. Media routinely used were: McConkey and Columbia agar, Chocolate PVX, Schaedler sheep blood, thioglycolate-enriched media (bio-Mérieux, France), and blood culture media ESP 80A and ESP 80N (Trek Diagnostic Systems, USA). Fungal cultures were done at the discretion of the attending physician. The microbiology of pleural effusions was classified as follows: aerobic Gram-positive bacteria, aerobic Gram-negative bacteria, anaerobic bacteria and other organisms.
The following data were collected for each patient: age, gender, predisposing factors, size and location of effusion, requirement of chest tube drainage, and biochemical and microbiological characteristics of pleural fluid. The size of the effusion was assessed on the posteroanterior radiograph by visually estimating the area of the hemithorax occupied by pleural fluid. Large effusions were defined as those that occupied 50% of the hemithorax.
Continuous data are reported as medians (25th-75th percentile). The χ2 and Kruskal-Wallis tests were used to compare groups for qualitative and quantitative variables, respectively. A two-tailed
From a total of 205 patients diagnosed of infectious pleural effusion, about 10%, 30% and 75% of typical, complicated parapneumonics and empyema respectively showed culture positive fluids. Specifically, the study population was comprised of 84 patients (41%) with positive cultures of pleural fluid. The median age was 61 (40-74) years, 33 (39%) patients were > 65 years of age, and male/female patient ratio was about 3:1. Excluded from analysis were 27 additional patients whose pleural fluid cultures showed growth of contaminant bacteria, including 9 cases of
Ninety-three microorganisms, including 62 (67%) aerobic Gram-positive bacteria, 22 (24%) aerobic Gram-negative bacteria, and 6 (6%) anaerobic bacteria were recovered from the 84 patients (Table 1). In the aerobic Gram-positive group, viridans streptococci (19 isolates),
aNumbers in parentheses indicate the number of isolates that were recovered in pure culture TPE, typical parapneumonic effusion; CPE, complicated parapneumonic effusion; RBC, red blood cell count; WBC, white blood cell count; LDH, lactate dehydrogenase; ADA, adenosine deaminase
An underlying disease or associated medical conditions were present in 58 (69%) patients, of which the most common were malignancy (16 patients, 19%), human immunodeficiency virus disease (10 patients, 12%), and chronic obstructive pulmonary disease (8 patients, 10%), followed by alcoholism (7 patients, 8%), diabetes (4 patients, 5%), and cirrhosis (2 patients, 2%). With regard to specific organisms, 41%, 53%, 83% and 86% of patients with
No chest tube drainage was inserted in 10 (12%) patients, from whom the following bacteria were isolated:
The fluid in culture-positive effusions was invariably an exudate. In more than 90% of cases, the pleural fluid differential white blood cell count revealed predominantly polymorphonuclear leucocytes. Overall, 63% (35/56) of culture positive fluids of parapneumonic origin, and in particular 74% (28/49) of post-pneumonic empyemas had an ADA level that exceeded the diagnostic cutoff for tuberculosis (40 U/L). When we moved from the initial pathophysiologic stage of a parapneumonic effusion (typical or non-complicated) to later stages (complicated and empyema), pleural fluid yielded higher white-cell counts, percentage of neutrophils, lactate dehydrogenase, and ADA, but lower pH and glucose content (Table 2). Likewise, positive bacterial cultures entailed more frequently an empyema (68%) than a complicated or uncomplicated parapneumonic effusion (20,5% and 11% respectively, p<0.001). In addition, when compared to the patients with typical parapneumonic effusions, a substantial percentage of patients with complicated parapneumonic effusions or empyema had large effusions (12% vs 65%, respectively, p<0.001).
aData are given as median (25th-75th percentile)
This study highlights the continuing importance of streptococci in parapneumonic effusions and empyema. Thus, viridans streptococci and
In eight separate comprehensive reports2,3,4,6,7,8,9, including this one, which represent 772 patients and 1201 microorganisms, aerobic Gram-positive, aerobic Gram-negative and anaerobic bacteria were isolated in 42%, 23% and 35% of cases, respectively. Of these,
Several comorbid conditions that alter systemic or local pulmonary host defenses such as malignancy, human immunodeficiency virus infection, and chronic obstructive pulmonary disease increase the risk of empyema. In our study, Gram-negative bacterial infection of the pleural space was associated with the higher incidence of underlying disease (86%). Conversely, in otherwise healthy adults, the bacteria most commonly causing pleural infection was
High levels of ADA, a diagnostic test for tuberculous pleuritis, were found in the pleural fluid of a significant proportion of patients with parapneumonic effusion and especially empyema. However, tuberculosis is most commonly suspected only in lymphocytic effusions, which easily exclude most of the parapaneumonic and empyema fluids10. The main problem in dealing with parapneumonic effusions is the selection of patients for pleural drainage11. Generally, when bacteria invade pleural space (fibronopurulent stage of a parapneumonic effusion) the ability to resolve the infection with antibiotics alone is lost. Thus, although not evaluated in prospective studies, expert consensus recommends that a positive pleural fluid culture warrants drainage of the pleural space12,13. We should stress that occasional patients with culture-positive pleural fluid can be successfully treated without chest tube drainage, specially if pleural effusion is small (a third or less of the hemithorax). Thus, a positive bacterial culture is a strong, but not an absolute indication for drainage14, although we clearly favor its use11.
José Manuel Porcel, MD, FACP, FCCP Department of Internal Medicine University Hospital Arnau de Vilanova Alcalde Rovira Roure 80 25198 Lleida (SPAIN) E-mail: firstname.lastname@example.org Phone.: 34 973 705262 Fax: 34 973 248754