A bacteriologic basis for the evolution and severity of empyema

The management of pediatric empyema remains controversial. An experimental study was undertaken to evaluate the role of bacteria in the evolution and severity of empyema, using specific bacteria that are pathogens of empyema in children. A rabbit model was used. The groups were Haemophilus influenzae (n = 9), Bacteroides fragilis (n = 8), the combination (n = 12), Staphylococcus aureus (n = 6), and control (n = 6). The total bacterial inoculum (10(8)) was constant. Diagnostic thoracentesis was performed at regular intervals. Characteristics of the empyema were evaluated when the rabbits were killed (at 4, 7, and 10 days). Most rabbits other than those of the mixed-bacteria group cleared the bacteria from their pleural cavities. Eleven of 12 mixed-bacteria animals had multiloculated empyemas; only one resolved spontaneously. In the other groups, the tendency was toward unilocular empyemas, which resolved by the 10th day in one third of the H influenzae animals, two thirds of the Bacteroides fragilis animals, and half the S aureus animals. The empyemas that persisted until the 10th day were in the exudative or fibrinopurulent stage, except for those of the mixed-bacteria group, all of which were in the advanced organizing stage. The amount of pleural debris and the degree of organization were significantly greater for the mixed bacteria group (P > .01). These findings support the clinical management of monobacterial empyema by simple drainage, whereas mixed aerobic-anaerobic empyemas may require more aggressive drainage procedures.