Title Risk factors and outcomes of Stenotrophomonas maltophilia bacteraemia: a comparison with bacteraemia caused by Pseudomonas aeruginosa and Acinetobacter

Stenotrophomonas maltophilia (SM) is an important nosocomial pathogen that exhibits intrinsic resistance to various antimicrobial agents. However, the risk factors for SM bacteraemia have not been sufficiently evaluated. From January 2005 to September 2012, we retrospectively compared the clinical backgrounds and outcomes of SM bacteraemic patients (SM group) with those of bacteraemic patients due to Pseudomonas aeruginosa (PA group) or Acinetobacter species (AC group). DNA genotyping of the SM isolates using the Diversilab system was performed to investigate the genetic relationships among the isolates. The SM, PA, and AC groups included 54, 167, and 69 patients, respectively. Nine of 17 patients in the SM group receiving trimethoprim-sulfamethoxazole prophylaxis developed SM bacteraemia. Independent risk factors for SM bacteraemia were the use of carbapenems and antipseudomonal cephalosporins and SM isolation within 30 days prior to the onset of bacteraemia. Earlier SM isolation was observed in 32 of 48 patients (66.7%) with SM bacteraemia who underwent clinical microbiological examinations. Of these 32 patients, 15 patients (46.9%) had the same focus of bacteraemia as was found in the previous isolation site. The 30-day all-cause mortality rate among the SM group (33.3%) was higher than that of the PA group (21.5%, p = 0.080) and the AC group (17.3%, p = 0.041). The independent factor that was associated with 30-day mortality was the SOFA score. DNA genotyping of SM isolates and epidemiological data suggested that no outbreak had occurred. SM bacteraemia was associated with high mortality and should be considered in patients with recent use of broad-spectrum antibiotics or in patients with recent isolation of the organism. Citation: Hotta G, Matsumura Y, Kato K, Nakano S, Yunoki T, et al. (2014) Risk Factors and Outcomes of Stenotrophomonas maltophilia Bacteraemia: A Comparison with Bacteraemia Caused by Pseudomonas aeruginosa and Acinetobacter Species. PLoS ONE 9(11): e112208. doi:10.1371/journal.pone.0112208 Editor: Muna Anjum, Animal Health and Veterinary Laboratories Agency, United Kingdom Received April 27, 2014; Accepted October 7, 2014; Published November 6, 2014 Copyright: 2014 Hotta et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: These authors have no support or funding to report. Competing Interests: The authors have declared that no competing interests exist. * Email: [email protected] Introduction Stenotrophomonas maltophilia (SM) is an emerging nosocomial pathogen. In a surveillance performed from 1997 to 1999 in the Asia-Pacific, Europe, Latin America, Canada, and the United States regions, SM was the third most frequently isolated nonfermentative gram-negative bacilli, following Pseudomonas aeruginosa (PA) and Acinetobacter species (AC) [1]. SM is intrinsically resistant to beta-lactams or aminoglycosides via the chromosomal resistance genes L1 and L2 beta-lactamase and aminoglycosidemodifying enzymes [2]. Trimethoprim-sulfamethoxazole (TMPSMZ) is the first-line therapeutic drug for the treatment of SM, and it is recommended that severe infections be treated with a high dose of TMP-SMZ, similar to the dose used to treat Pneumocystis jirovecii [2]. Thus, the therapeutic options for SM are quite different from those available for other non-fermentative gramnegative bacilli, and the appropriate antimicrobial therapy is often delayed [3]. Therefore, a high crude mortality rate among SM bacteraemic patients has been reported, ranging from 14% to 69% [4]. Several studies have evaluated the risk factors for SM bacteraemia, but these studies have involved small populations or patients with specific medical conditions, such as haematological malignancies [5–9]. No study has compared SM bacteraemia in all hospitalised patients with bacteraemias due to PA or AC, which are the most important nosocomial pathogens. To elucidate the clinical characteristics of SM bacteraemia, we compared the antimicrobial susceptibility, clinical backgrounds, and prognostic factors of SM bacteraemic patients with those of patients suffering from bacteraemia due to Pseudomonas aeruginosa (PA) or Acinetobacter species (AC). The risk factors for 30-day mortality were evaluated in the SM bacteraemic patients. For the SM isolates, DNA genotyping was also conducted to investigate the genetic relationships among the SM isolates.