Hemonc xam
Stenotrophomonas maltophilia
Bacteremia in Hematology-Oncology Patients at The Toronto Hospital - A Case Control Analysis Implicating a Central Line Related Source
S. Fung, E. Choi, , A. Humar, H. Dedier, J. Louvaris, P. Savage, I. Campbell, J. Strauss, M. Garcia, J. Brunton J. Conly
The Toronto Hospital Infection Control Unit,
Department of Microbiology and Division of Infectious Diseases ,
University of Toronto
Introduction
Stenotrophomonas (Xanthomonas) maltophilia (Sm) is an aerobic multidrug-resistant gram-negative bacillus
Ubiquitous in soil, water and moist environments
1960: First described by Ryschenkow as Pseudomona maltophilia based on polar flagellae
1983: Swings et al proposed Xanthomonas genus based on rRNA and G+C content differences
1992: Current Stenotrophomonas genus based on phenotypic differences and resistance patterns
Considered a culture contaminant in the past
Increasing importance in compromised patients
Typically causes severe infection in debilitated hosts
Spectrum of disease includes bacteremia, endocarditis, meningitis, ocular infections, respiratory tract infections, urinary tract infections and wound infections
Antibiotic resistance conferred by low outer membrane permeability and production of broad-spectrum B-lactamases
Risk Factors for Sm disease:
neutropenia less than or equal to 1.0 x 109/L
indwelling central venous catheter
recent treatment with broad-spectrum antibiotics
previous treatment with corticosteroids
An increase in the number of blood isolates of this organism in the second half of 1995 led us to investigate the emerging role of this pathogen in our hematology-oncology population.
Materials and Methods
Outbreak Investigation
- review of Microbiology Laboratory records and Ulticare HIS computer records
- environmental screening of patient rooms and the Oncology OP Clinic
- stool carriage screening of bacteremic patients using imipenem agar as selective media
- strain relatedness determined using Pulsed-Field Gel Electrophoresis (PFGE) and Randomly Primed Polymerase Chain Reaction (RP-PCR)
- PFGE macrorestriction of genomic DNA with Dra1
- RP-PCR primers:
5'CTGGCGGCTG 3'
5'CAGGCGGCGT 3'
Case-Control Study
- to determine potential risk factors for bacteremia in our heme-onc patient population
- cases defined as Sm bacteremia in inpatients on the oncology ward between July-Nov. 1995
- bacteremic controls defined as ward contemporaneous inpatients with bacteremia due to other gram-negative bacilli
- nonbacteremic controls defined as ward contemporaneous inpatients with fever but without culture-proven bacteremia
- statistics analyzed using Epi Info
Results
Outbreak Investigation
- July-November 1994 vs July-November 1995: Sm increased from 6% (3/47) to 33% (20/61) of all gram-negative bacteremias
- Sm was the second most frequent gram-negative isolate for 1995
- Screening cultures from patients' rooms from sinks, showers, soap, etc.) revealed 1 Sm isolate
- Outpatient clinic revealed 1 isolate: irregularities found with saline flush
- Perirectal screening swabs revealed no Sm
- Molecular subtyping results were analyzed by visual inspection
- PFGE of the 2 environmental isolates showed they were distinct: different from each other and from the outbreak isolates
- PFGE and RP-PCR results for 19 outbreak strains revealed no common genotype
Results
Susceptibility of Isolates
- Septra and Timentin appear to have the greatest activity against Sm
- Susceptibility to piperacillin (MIC < or = 64 mg/l) decreased from 87% to 36% between 1990-4
- Susceptibility to ceftazidime (MIC < or = 8 mg/l) decreased from 36% to 26% between 1990-4
Case-Control Study
For Sm vs bacteremic controls, no. of hospitalizations (4.8 vs 1.4), 7 or more days of ciprofloxacin use, 4 or more visits to OP clinic and polymicrobial blood culture all significantly associated with Sm infection
For nonbacteremic controls, no. of prior hospitalizations, length of stay prior to bacteremia, use of tobramycin/cefazolin, and central venous catheter duration were all significant factors
Conclusions
S. maltophilia is increasing in importance as a cause of bacteremia in oncology patients at TTH.
Oncology patients bacteremic with S. maltophilia have a significantly higher mortality when compared to nonbacteremic controls.
The multiple genomic banding patterns of the outbreak isolates, as shown by PFGE and RP-PCR, indicate no common environmental source for the outbreak in 1995, although polymicrobial bacteremia suggests a potential line-related source.
The association with outpatient clinic visits warranted a review of patient care policies in this area.
After the investigation initiated by the Infection Control Unit, greater attention to line care by caregivers resulted in a return to baseline frequency of Sm bacteremia in this patient population (2 cases for all of 1996).
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