Risk factors for emergence of Stenotrophomonas maltophilia in cystic fibrosis.

The number of patients with cystic fibrosis (CF) whose sputum culture has yielded Stenotrophomonas maltophilia has increased in the last 5 years at St. Christopher's Hospital for Children. We conducted a case-control study to determine risk factors for recovery of S. maltophilia in respiratory secretions from patients with CF. We reviewed the outpatient and inpatient records of patients colonized with S. maltophilia between 1993 and 1997, and of age-matched (at time of initial recovery of S. maltophilia) control patients with CF who had never had a positive sputum culture for S. maltophilia. Variables included age at time of CF diagnosis, gender, severity of CF (based on Shwachman-Kulczycki (S-K) scores and spirometry), frequency of hospitalizations, use of oral, intravenous, or inhaled antibiotics, and use of oral or inhaled corticosteroids in the 2 years prior to the first isolation of S. maltophilia from respiratory secretions. Statistical methods included stepwise logistic regression to determine risk factors for acquisition of S. maltophilia. During the study period, 58 patients with CF had a positive sputum or deep throat culture for S. maltophilia. The distribution of S. maltophilia acquisition by year increased from 7 patients in 1993 (incidence, 2.8%) to 16 in 1997 (incidence, 6.2%). Patients positive for S. maltophilia were found to have significantly worse growth parameters, S-K score, and spirometric values than S. maltophilia-negative CF controls (P < 0.05). Stepwise logistic regression demonstrated that treatment with long-term antibiotics (P = 0.0016) and number of days of intravenous antibiotic therapy (P = 0.035) were significant risk factors for S. maltophilia colonization in our group of CF patients. We conclude that patients with CF whose respiratory secretions yield S. maltophilia have an overall worse clinical status at the time of initial S. maltophilia isolation than noncolonized patients, and that preceding treatment with antibiotics may have predisposed them to the acquisition of this bacterium in their respiratory secretions.