Improving detection of extended-spectrum beta-lactamase-producing bacteria in a deployed setting.
Beta lactamases (Health aspects)
Drug resistance (Research)
Drug resistance (Health aspects)
Antibiotics (Health aspects)
Bacterial infections (Risk factors)
Bacterial infections (Diagnosis)
Aldous, Edgie-Mark A. Wade K.
Hamilton, Lanette R.
|Publication:||Name: U.S. Army Medical Department Journal Publisher: U.S. Army Medical Department Center & School Audience: Professional Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 U.S. Army Medical Department Center & School ISSN: 1524-0436|
|Issue:||Date: July-Sept, 2011|
|Topic:||Event Code: 310 Science & research|
|Product:||SIC Code: 2834 Pharmaceutical preparations|
|Geographic:||Geographic Scope: United States Geographic Code: 1USA United States|
Extended-spectrum beta-lactamase (ESBL) production in bacterial isolates is becoming a worldwide problem. ESBL-producing organisms have been associated with limited therapeutic treatment options due to their broad spectrum resistance to ureidopenicillin, third-generation cephalosporins, and aztreonam. (1,2) Furthermore, these organisms can have a severe impact in wound, burn and bloodstream infections, often resulting in adverse outcomes. (3-6) In the United States, 75% of medical centers report the occurrence of EBSL producers, and there has been a relative increase in isolation of ESBL-producing Escherichia coli (E. coli) around the world. (7,8) Furthermore, overseas travel, particularly to India, Africa, and the Middle East, has also been identified as a risk for ESBL producer acquisition. (7) This trend is worrisome with the continued worldwide deployments of US service members in support of Operations New Dawn and Enduring Freedom, and Operation Enduring Freedom--Horn of Africa. In these regions there is a predisposition to infection by ESBL-producing organisms among US service members due to their increased exposure to battle-trauma injuries. (9) According to the National Nosocomial Infection Surveillance System, 40% of the isolated ESBL producers in US medical centers were obtained from intensive care units. (10) This is of particular interest because the intensive care unit is the hospital section responsible for proving care to severely injured US service members.
The phenotypic characteristic of ESBLs is concomitant/ simultaneous resistance to aztreonam, cefotaxime, ceftriaxone, and ceftazidime. (10) The Clinical Laboratory Standards Institute (http://www.clsi.org/) recommends a confirmatory test to identify ESBL-producing organ isms, which increases the time required to obtain results. (11,12) This delay causes the clinician to rely on empiric therapy, which may or may not be sufficient depending on the accuracy of the local antibiogram. Studies have shown that inadequate initial antimicrobial therapy is a significant predictor of mortality, underscoring the importance of accurate antimicrobial susceptibility reporting. (6,8) Thus, early identification of such organisms at the combat support hospital (CSH) level is critical to avoid inappropriate treatment prior to evacuation, which is especially important since many such injuries are initially treated empirically. (13)
Currently the microbiology augmentation set (N403) normally deployed with the CSH uses the Negative Breakpoint Combo Panel Type 30 (NBPC30) (Siemens Healthcare Diagnostics Inc, Deerfield, IL). This panel is able to analyze growth and susceptibility patterns of rapidly growing aerobic and facultative gram-negative bacteria with a turnaround time of 48 to 72 hours. Studies have shown its effectiveness in gram-negative organism identification and susceptibility. (14,15) Similarly, Siemens produces the Negative Breakpoint Combo Panel Type 41 (NBC41). This panel is similar in many respects to the NBPC30 panel and is also available as an alternative for gram-negative identification and susceptibility testing. Standard operating procedures for the panels are published in the field laboratory information program disk, (16) but the default in many in-theater standard operating procedures is use of the NBCP30 for gram-negative identification and susceptibility testing (ID/AST).
The objective of this study was to compare and evaluate the efficiency of the NBPC30 and the NBC41 in the identification of ESBLs against the gold standard method. We performed bacterial ID/AST of isolated Enterobacteriaeceae in our laboratory using both panels. The reference method was the Kirby-Bauer method using Clinical Laboratory Standards Institute guidelines. Sensitivities and specificities of each panel were also calculated.
MATERIALS AND METHODS
Facilities and populations were previously described by Yun et al. (17) Patients were seen at the Ibn Sina hospital tertiary care facility in Baghdad, Iraq, which treated a wide variety of patient populations including US military personnel, US civilians, coalition forces, foreign national contract employees, Iraqi local nationals, and detainees. The hospital also provides a spectrum of surgical, intensive, emergent, and outpatient care. The colocated outpatient clinic provides specialty services such as dermatology and physical therapy. Blast injuries and gunshot wounds are the most common cases seen. (9)
Strains included in this study were isolated using the CSH's normal microbiology laboratory operating procedures. The types of strains isolated and the degree of resistance is described elsewhere. (18) Isolates were initially identified as gram-negative organisms from the family Enterobacteriaceae using the NBPC30 panel. Any isolated members of the Enterobactericeae were subsequently tested on the NBC41. Panels were read using the Microscan Autoscan 4 (Siemens Healthcare Diagnostics Inc, Deerfield, IL).
RESULTS AND COMMENT
Seventy-nine potential ESBL-producing organisms were included in this study, with the most isolated organism was E. coli, followed by K. pneumoniae. Other Enterobacteriaceae species such as K. oxytoca, and Proteus mirabilis (P. mirabilis) were also isolated. Common sources include respiratory, wound, urine, and blood, with wound and urine being the most prevalent. As the CSH mostly treats battle-related traumatic injuries, wound cultures were among the most prevalent culture tests requested (Table 1).
When compared to previous studies, our data showed that the NBPC30's sensitivity and specificity were better than those previously reported by Wiegand et al. (15) They compared the performance of the VITEK (bioMerieux, Inc, Durham, NC), Phoenix (BD Diagnostic Systems, Sparks, MD), and the MicroScan, with the MicroScan's sensitivity at 84%. However, their studies did include 150 samples, twice the number tested in this study. Another study by Linscott et al evaluated the MicroScan ESBL plus ESBL confirmation panel. This panel has similar antibiotics to the NBC41 with 2 exceptions; addition of cefpodoxime and cefotetan, and use of minimum inhibitory concentration determination. They reported 100% sensitivity and 98% specificity in ESBL detection. (20) This panel is available for use in the N403 kit. A study comparing the performance of the NBC41 to the ESBL confirmation panel will allow a direct evaluation of the former's performance in ESBL detection. Furthermore, additional studies with more isolates are required to determine the positive and negative predictive values of the panels.
Our data showed the NBC41 to be superior in detecting ESBL producers when compared to the currently used NBPC30 panels. The NBC41 panels also showed better concordance with the Kirby-Bauer method and did not show discrepancies in identification. Furthermore, the panel also tests 10 more antibiotics compared to the NBPC30 panel. As previously described, the main difference is the high utilization of antibiotic breakpoints in the NBC41 panel. This provides the clinician with a qualitative measure of susceptibility, which may be sufficient in most cases. Furthermore, although the MicroScan ESBL and ESBL confirmation panel is available for order with the N403 kit, it suffers from the same problem of additional turnaround time as the NBPC30 panel. Although evaluated as a valuable tool for ESBL confirmation, (21) this panel cannot perform bacterial identification and ESBL confirmation simultaneously. In comparison, the NBC41 panel eliminates the need to use additional confirmatory panels, shortening ID/ AST of ESBL-producing organisms to 48 hours. Our study shows that using the NBC41 can substantially decrease turnaround time in ID/AST, while providing a confirmed result of the status of an isolate as an ESBL-producing organism.
In theater, the N403 microbiology augmentation kit currently includes a MicroScan Autoscan 4 for routine bacterial identification. This equipment set is fielded with dried panels for the identification of gram-positive and gram-negative organisms. Currently, many in-theater labs use the NBPC30 as the default panel for identification of gram-negative organisms. However, due to the nature of the infection types ESBL-producing organisms cause, we highly recommend using the NBC41 as the primary panel for identification of gram-negative organisms. This panel is a better choice to provide crucial susceptibility data to the health care provider with its capability to test more antibiotics. Our data shows that isolates can be reported as confirmed ESBLs with confidence using the NBC41 panel. Benefits of this change include reduced turnaround time for antibiotic susceptibilities and, as a consequence, effective antibiotic treatment management for the patient.
We thank MAJ Miguel Arroyo-Cazurro of the 86th Combat Support Hospital for his contribution of the panel pictures.
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CPT Co is with the Division of Experimental Therapeutics at the Walter Reed Army Institute of Research, Silver Spring, MD.
LTC Aldous, CPT Keen, and CPT Robinson are with the Dept of Pathology and Area Lab Services at the Brooke Army Medical Center, Fort Sam Houston, TX.
COL Hamilton is participating in a Long-Term Health Education Training program with the Division of Laboratory and Genomic Medicine, Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO.
Table 1. Breakdown of isolates (N=79) by species and specimen source. Organism Blood Peritoneal Respiratory Fluid Escherichia coli 1 0 6 Klebsiella pneumoniae 8 0 9 Klebsiella oxytoca 0 0 0 Proteus mirabilis 0 1 0 Total 9 1 15 Organism Skin stool Wound Escherichia coli 2 6 14 Klebsiella pneumoniae 0 0 8 Klebsiella oxytoca 1 0 1 Proteus mirabilis 0 2 1 Total 3 8 24 Organism Urine Total Escherichia coli 13 42 Klebsiella pneumoniae 4 29 Klebsiella oxytoca 0 2 Proteus mirabilis 2 6 Total 19 79 Table 2. Specificities, PPV, and NPV of MicroScan panels for the detection of ESBL production with disk diffusion as a reference method (isolates N=79). Panel Positive Negative False False Positives Negatives NBPC30 58 21 5 8 NBC41 60 19 1 2 Panel sensitivity specificity (%) (%) NBPC30 86.9 72 NBC41 96.7 89
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