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Characteristics of 12 Case-patients With Bacteremia Caused by Alcaligenes xylosoxidans*

Figure 1.  

Scanning electron micrograph of lumen of segment of central venous catheter removed from an asymptomatic patient. Biofilm contains rod-shaped bacteria (Alcaligenes xylosoxidans) in association with fibrinlike material on the catheter surface.

Figure 2.  

Pulsed-field gel electrophoresis of isolates from patients with Alcaligenes xylosoxidans bloodstream infection. Lane 1, laboratory standard; lanes 2 and 6, community strains of A. xylosoxidans; lanes 3–5 and 7–13, outbreak strains; lane 14, central venous catheter (CVC) port biofilm outbreak strain; lane 15, CVC port outbreak stain.

Alcaligenes xylosoxidans Bloodstream Infections in Outpatient Oncology Office: Methods



The outbreak investigation focused on Office B. To identify all patients associated with Office B who had had a positive A. xylosoxidans culture, we requested a review of medical records and laboratory reports.

Matched Case–Control Study

A matched case–control study was performed to determine risk factors for infection. A case-patient was defined as a patient of Office B who had a positive A. xylosoxidans blood culture from November 2001 through January 2002. Controls were defined as patients who had no symptoms or signs of bloodstream infection (fever, chills, rigors, myalgias, nausea, vomiting, weakness, or hypotension). For each casepatient, 5–7 controls were randomly selected and matched by the closest date of their visits to Office B to the casepatient's date of visit. Variables included age, sex, underlying diagnosis, intravenous medications received, peripheral white blood cell counts, presence and type of central venous catheter (CVC), clinic visits, hospitalization dates, symptoms, and types of invasive procedures. Data were collected on standardized forms and analyzed by using Epi Info 2000 version 1.1.2 (Centers for Disease Control and Prevention [CDC], Atlanta, GA, USA); odds ratios were used to estimate risk, t tests were performed for continuous variables, and p <0.05 indicated statistical significance.

Prospective Cohort Study

To identify possible A. xylosoxidans bloodstream infection, ACDC conducted prospective blood culture surveillance. On February 15, 2002, all patients with a CVC who had visited Office B since November 2001 were sent a letter requesting them to have a culture performed on blood drawn through the CVC. CVCs were removed from those whose culture results were positive.

Environmental Investigation

On January 17, 2002, numerous open containers (multidose 30-mL vials of heparin; 100-mL and 150-mL bottles of saline; and containers of alcohol, hydrogen peroxide, betadine, and iodine) were collected and sent to the Los Angeles County Public Health Laboratory for analysis. On February 15, 2002, environmental samples and swabs were collected for culture from work surfaces (e.g., countertops, sinks, hoods, kitchens) and from tap water and hands of healthcare workers who accessed CVCs, collected blood, prepared flushes, or administered chemotherapy.

Infection Control

During January and February 2002, we made several site visits to Office B to observe procedures, review medical records, and interview the office staff. Specifically, we observed procedures for preparation and administration of intravenous medications and asked office staff about level of technical training, experience, and license status.

Molecular Studies

Blood isolates of A. xylosoxidans from case-patients were obtained from Hospital A's laboratory. For comparison, all A. xylosoxidans isolated from patients from Los Angeles County in the past 6 months were obtained from a large local reference laboratory. Pulsed-field gel electrophoresis (PFGE) was performed at the Los Angeles County Public Health Laboratory by using standard methods[18] for Salmonella spp. with the exception that isolates were digested with XbaI and SpeI. PFGE pattern comparisons were performed visually by using criteria established by Tenover et al.[19]

Examination of CVC for Biofilm

A CVC (PASport, a single-lumen, 6 French catheter with an under-the-skin titanium port; SIMS Deltec, Inc., St. Paul, MN, USA) was surgically removed from an asymptomatic patient identified in the prospective cohort study. Aseptic methods were used. The distal lumen opening was clamped with a sterile hemostat to retain the liquid within the lumen, and the catheter was placed in a sealed, sterile container and shipped overnight to CDC in Atlanta for processing within 24 hours of collection. At CDC, the CVC was placed into a Class II Biological Safety Cabinet, and a 1-cm segment was removed with a sterile scalpel. This segment was cut lengthwise to expose the lumen, and the individual pieces were placed into 5% glutaraldehyde (Ted Pella, Redding, CA, USA) in 0.67 M cacodylate buffer, pH 6.2, and processed for scanning electron microscopy.[20] Samples were examined by using a Philips XL 20 Scanning Electron Microscope (FEI Company, a subsidiary of Philips, Hillsboro, OR, USA). The remaining catheter attached to the titanium port was clamped, and the outer surface was cleaned with a 70% alcohol wipe, disinfected, and processed to recover biofilm organisms.[20] The recovered organisms were plated on trypticase soy agar containing 5% sheep blood (blood agar; Becton, Dickinson, Sparks, MD, USA). Plates were incubated for up to 72 h at 35°C and then examined. Colonies were spread onto blood agar for subculture and identified by using standard clinical microbiologic methods.[21] Biofilm isolates were also characterized by PFGE (methods described above).

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