TAIPEI, TAIWAN--The microbiology of thoracic empyema may be changing, new data suggest. For example, researchers at the National Taiwan University Hospital in Taipei found increasing rates of fungal empyema in a recent study of inpatients at their hospital.[1]

The infections often developed in the intensive care unit (ICU) and were associated with an extremely high mortality rate (73%), especially among the immunocompromised. A large proportion of these infections occurred in patients receiving broad-spectrum antibiotics, which raise the risk of fungal infection by altering the flora in the gastrointestinal (GI) tract.

A second study at the same hospital examined patients with bacterial thoracic empyemas; it found that aerobic gram-negative bacilli, such as Klebsiella pneumoniae, have replaced aerobic gram-positive and anaerobic organisms as the leading pathogens.[2] Furthermore, the mortality rate was markedly higher among the patients with K pneumoniae infections than among the other patients in the study.

MORE FUNGAL CASES IN AMERICA, TOO?

It is unclear whether fungal thoracic empyemas are becoming more common in American hospitals. "As far as I know, there has not been a study in United States that has looked specifically at fungal empyemas," said Steven Sahn, MD, in an interview with PULMONARY REVIEWS. However, he added, the Taiwanese data provide a valid warning for US physicians, who often prescribe broad-spectrum antibiotics for their inpatients. Dr. Sahn is a Professor of Pulmonary and Critical Care Medicine at the Medical University of South Carolina in Charleston.

In performing the study of fungal empyema, Shiann-Chin Ko, MD, and colleagues retrospectively analyzed the records of patients treated for that condition at the National Taiwan University Hospital between January 1990 and December 1997. A total of 67 cases were found; two thirds of the patients were male. Only one case occurred in each of the first two years of the study. The incidence then steadily increased, to six cases in 1992 and seven in 1993. More than 10 cases were recorded annually from 1994 through 1997.

The fungal thoracic empyemas were nosocomial in 56 (84%) of the patients; they were ICU-acquired in 43 (64%). Among the leading causes were previous abdominal surgery, GI perforation, and bronchopulmonary infection. Ninety percent of the patients had underlying medical conditions; the most common was immunocompromise related to malignancy, diabetes, long-term corticosteroid use, or other factors.

Forty (60%) of the patients had received broad-spectrum antibiotics for more than a week before the fungal empyemas developed. "If we continue to treat very sick patients in this country with broad-spectrum antibiotics, we also will probably see more fungal empyemas," commented Dr. Sahn.

When the patients' pleural fluid was analyzed, 73 fungal isolates were recovered. Candida species (especially C albicans and C tropicalis) were the most common, followed by Torulopsis glabrata and by Aspergillus and Cryptococcus species. Fungemia developed in 18 patients.

Despite treatment--primarily, systemic antifungal therapy (amphotericin B and/or fluconazole) and closed drainage--49 (73%) of the patients died after a mean of 66 days in the hospital. Forty-three of the deceased were immunocompromised. Multivariate analysis found a significantly greater risk of death in these patients (relative risk [RR], 1.58) and in those with respiratory failure (RR, 2.31). The mean duration of hospital stay for all patients was 66 days.

KLEBSIELLA AND DIABETES

In the second study, Kuan-Yu Chen, MD, and colleagues retrospectively analyzed the records of patients treated for acute thoracic empyema at the National Taiwan University Hospital between January 1989 and December 1998 to identify those who had bacterial infections. A total of 171 patients met the study criteria. These patients, whose mean age was 65 years, were predominantly male (3:1 ratio).

"People generally don't get empyemas unless they have an underlying disease," Dr. Sahn pointed out. "In this study, diabetes was the most common one, affecting 22% of the patients." Other prominent underlying conditions included malignancy (18%), previous lung disease (14%), and central nervous system disorders (11%).

Pleural effusion cultures were positive in 139 patients and yielded 163 types of bacteria. Fifty-nine patients had aerobic gram-negative bacteria, 47 had aerobic gram-positive organisms, 14 had anaerobic bacteria, and 19 had mixed infections.

The most frequently isolated pathogen was K pneumoniae, which appeared in about 24% of the patients. "I am not surprised," said Dr. Sahn, "because Klebsiella infection has a predilection for patients with diabetes." Indeed, patients with this pathogen were significantly more likely than those without to have diabetes (44.1% vs 15.3%) or to be an alcoholic (8.8% vs 0.7%).

Many patients required intrapleural fibrinolytic therapy, thoracic surgery, or both, in addition to antibiotics and chest tube drainage. The mean length of hospital stay was 31 days--about half that required for a fungal thoracic empyema.

The death rate was strongly influenced by the causative organism. Mortality was 22% among the patients with aerobic gram-negative bacteria, 6.4% among those with aerobic gram-positive organisms, and 15.7% among those with mixed infections. No deaths occurred among the patients with anaerobic infections. Those with K pneumoniae had a significantly higher mortality rate than did the other patients (26.5% vs 9.5%).

Because of their findings, the authors of both studies recommend more aggressive treatment for thoracic empyemas. This practice is already widespread in the United States, Dr. Sahn said. In patients with acute thoracic empyemas, for example, it is common to recommend surgery after only two or three days of failed chest tube drainage, as opposed to the 10-day average in Dr. Chen's study.

--Timothy Begany

References
1. Ko S-C, Chen K-Y, Hsueh P-R, et al. Fungal empyema thoracis: an emerging clinical entity. Chest. 2000;1672-1678.
2. Chen K-Y, Hsueh P-R, Liaw Y-S, et al. A 10-year experience with bacteriology of acute thoracic empyema: emphasis on Klebsiella pneumoniae in patients with diabetes mellitus. Chest. 2000;117:1685-1689.

Return to table of contents