Cluster of Stenotrophomonas maltophilia endocarditis after prosthetic valve replacement

Early postoperative prosthetic valve endocarditis due to Stenotrophomonas maltophilia was diagnosed in seven patients (two men) aged from 68 to 84 years (mean age 78.1 years) over a three-year period. All patients had undergone aortic valve replacement. S. maltophilia was isolated from at least two blood cultures per patient. Four patients experienced CNS embolic complications. Three patients died. All patients were treated with ceftazidime, one in combination with amikacin, one with ciprofloxacin and one with levofloxacin. Because a common source of infection in the operating theater was suspected, 24 environmental samples were taken, of which two contained S. maltophilia. Six of the seven clinical isolates from the patients and two isolates from the environment were analyzed using molecular typing by pulsed-field gel electrophoresis (PFGE). The patients' isolates were resistant to gentamicin, ciprofloxacin, trimethoprim/sulfamethoxazole and, except in one case, to amikacin and piperacillin/tazobactam and susceptible to ceftazidime and levofloxacin. In contrast, the environmental isolates were resistant to ceftazidime, showed intermediate susceptibility to ciprofloxacin, and were susceptible to trimethoprim/sulfamethoxazole. PFGE demonstrated indistinguishable or closely related (1-3 band difference) PFGE patterns in isolates from the patients, but a different pattern in the environmental isolates. No common source of infection was found despite intensive investigation. Extensive cleaning and other measures of infection control were carried out and no new cases were recorded in the two year follow-up period.