An Urgent Problem of Aerobic Gram-Negative Pathogen Infection in Complicated Parapneumonic Effusions or Empyemas

Abstract

Complicated parapneumonic effusion or empyema is a troublesome disease with a high mortality. The most common involved microorganisms seem to have changed over recent decades, influenced by the introduction of new antibiotics, and the increase of immunocompromised hosts, and the elderly population. More epidemiological studies on the current bacteriology are needed to help us to empirically select adequate antibiotics. A retrospective study via chart review in a university-affiliated tertiary medical center was conducted to assess the underlying bacterial pathogens and outcome of patients with complicated parapneumonic effusions or empyemas. During the 43-month study period (from December 2000 to June 2004), 304 patients were diagnosed with complicated parapneumonic effusions or empyemas and the mortality of these patients was 23% (69/304). Among these 304 patients, a total of 292 microorganisms were cultured from the pleural fluid samples of 207 patients (to yield a positive microbiological culture rate of 68% (207/304). Isolated bacteria included aerobic Gram-negative bacteria (n=129), aerobic Gram-positive bacteria (n=105), anaerobic bacteria (n=51), and M. tuberculosis (n=7). Of these aerobic bacterial infections, Gram-negative bacteria were isolated more frequently from the older population and involved a significantly higher mortality rate and longer stay, compared to those with other bacteria (p=0.001 and p<0.001 respectively). The increasing incidence of infection with aerobic Gram-negative pathogens may cause more critical conditions in complicated parapneumonic effusions or empyemas.