Pleural fluid evaluation is important both in diagnosis and in guiding treatment in such cases. Pleural fluid collections are defined as transudative or exudative based on biochemical evaluation. Evaluation includes cell type and differential, pH, glucose, protein and LDH. Gram-stained smear needs to be performed on all specimens at the time of culture. Empyema is exudative, typically with low glucose and high LDH (Table 2 on page 64) (2).
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Figure 3. Tenacious exudate in the intrapleural space at the time of VATS in a child with empyema.
Changing Epidemiology and Antibiotic Decision Making
Data presented by Finland and Barnes in 1978 confirmed that S. pneumoniae, group A streptococcus (GAS), and Staphylococcus aureus were the most commonly identified pathogens in empyema cases in 1935, with S. aureus emerging in the 1950s (3). Most literature from the 1960–1980s detailing etiology of pneumonia with pleural empyema continued to emphasize the role of S. aureus in such cases. In all reviews, staphylococcal pneumonia is noted primarily to be a disease of infants. In 1 review of 100 cases of staphylococcal pneumonia, the median age was 5 months, 78 patients being below 1 year of age (4). Chartrand and McCracken analyzed 79 cases of staphylococcal pneumonia and noted that in about 75% of cases, staphylococcal pneumonia was a primary pneumonia in infants with a median age of 6 months. In this study, older children were more likely to have pulmonary involvement as a secondary finding in the setting of disseminated staphylococcal disease. A pleural effusion was found in 80% of infants with primary pneumonia and in 61% of those with secondary disease, thus providing the tip-off of a more serious process to the clinician (5). A high index of suspicion for S. aureus in the young infant with pneumonia is important, as physicians need to expect a rapidly progressive clinical course. Those infants frequently require ventilatory support, alteration in antibiotic choice, and the prompt recognition of pleural complications including pneumothoraces and pneumatoceles.
Data in the 1990s emphasized the role of multidrug resistant pneumococcus as a pathogen in empyema. In a recent review of cases in the postpneumococcal conjugate disease era, pneumococcus remained the most commonly confirmed etiologic agent, with other gram-positive pathogens, including GAS and S. aureus, also documented (6). Despite widespread implementation of pneumococcal conjugate vaccine (PCV), and a population based surveillance study in the US that suggested that adding PCV to the childhood immunization schedule was associated with a 10-fold greater reduction in pneumonia (7), serious pneumonia caused by S. pneumoniae continued to be reported. The prevalence of serotype 1 and 3 as the etiologies of such infections may limit the utility of the current vaccine. One study from Greece demonstrated that the most common serotypes causing bacteremic pneumonia were 14, 6B, 1 and 19F (8). Childhood empyema in the UK is noted to be increasing, and a recent study of 47 empyema cases confirmed pneumococcus as the major pathogen, with over half caused by serotype 1 (9).
More recent data suggest yet another change to the epidemiology of empyema. Schultz et al. from Houston, TX, reviewed a decade of experience from 1993–2002, and while they identified a decrease in total cases of empyema, the emergence of methicillin-resistant S. aureus (MRSA) infection was noted (10).
While MRSA has long been considered an important pathogen in the etiology of healthcare-associated infection, experience in our institution also confirms the appearance of an increasing number of cases of community-acquired MRSA disease. Vancomycin is clearly part of the treatment regimen in the child at risk for staphylococcal pneumonia, though many have utilized clindamycin for the non–critically ill patient. The increase in such cases clearly has important implications for treatment decisions, as MRSA with inducible clindamycin resistance is not yet recognized in every facility. Data are not available to confirm the utility of trimethoprim-sulfamethoxazole in serious community-aquired MRSA infections, and the role for newer antibiotics, such as linezolid, has not been clearly defined.