Within-subject interlaboratory variability of QuantiFERON-TB gold in-tube tests.

BACKGROUND: The QuantiFERON®-TB Gold In-Tube test (QFT-GIT) is a viable alternative to the tuberculin skin test (TST) for detecting Mycobacterium tuberculosis infection. However, within-subject variability may limit test utility. To assess variability, we compared results from the same subjects when QFT-GIT enzyme-linked immunosorbent assays (ELISAs) were performed in different laboratories. METHODS: Subjects were recruited at two sites and blood was tested in three labs. Two labs used the same type of automated ELISA workstation, 8-point calibration curves, and electronic data transfer. The third lab used a different automated ELISA workstation, 4-point calibration curves, and manual data entry. Variability was assessed by interpretation agreement and comparison of interferon-γ (IFN-γ) measurements. Data for subjects with discordant interpretations or discrepancies in TB Response >0.05 IU/mL were verified or corrected, and variability was reassessed using a reconciled dataset. RESULTS: Ninety-seven subjects had results from three labs. Eleven (11.3%) had discordant interpretations and 72 (74.2%) had discrepancies >0.05 IU/mL using unreconciled results. After correction of manual data entry errors for 9 subjects, and exclusion of 6 subjects due to methodological errors, 7 (7.7%) subjects were discordant. Of these, 6 (85.7%) had all TB Responses within 0.25 IU/mL of the manufacturer's recommended cutoff. Non-uniform error of measurement was observed, with greater variation in higher IFN-γ measurements. Within-subject standard deviation for TB Response was as high as 0.16 IU/mL, and limits of agreement ranged from -0.46 to 0.43 IU/mL for subjects with mean TB Response within 0.25 IU/mL of the cutoff. CONCLUSION: Greater interlaboratory variability was associated with manual data entry and higher IFN-γ measurements. Manual data entry should be avoided. Because variability in measuring TB Response may affect interpretation, especially near the cutoff, consideration should be given to developing a range of values near the cutoff to be interpreted as "borderline," rather than negative or positive.

Improving detection of extended-spectrum beta-lactamase-producing bacteria in a deployed setting.

INTRODUCTION: Organisms that produce extended-spectrum beta-lactamase (ESBL) are significant causes of infection among deployed service members. These specific organisms have increased resistance to several antibiotics, limiting the choice of therapy for the provider. Currently, the deployed microbiology lab uses, by default, the Siemens NBPC30 panel to identify and measure antibiotic susceptibility of gram-negative organisms. However, when an ESBL is suspected, additional confirmatory testing is performed, during which time the health care provider is forced to use broad spectrum antibiotics to protect the patient from infection. In this study, we evaluated the NBPC30 and NBC41 panels for their ability to rapidly and accurately detect ESBL-producing organisms. METHODS: Identification and antimicrobial susceptibility testing of 79 strains of Enterobacteriaceae isolated from patients treated at Ibn Sina tertiary hospital (Baghdad) were performed using the NBPC30 and NBC41 panels. These results were confirmed using a Kirby-Bauer disk diffusion reference method described by the Clinical Laboratory Standards Institute. Sensitivities and specificities of the panels were determined in relation to this reference method. RESULTS: Sensitivity and specificity of the NBC41 were 96.7% and 89%, while they were 86.7% and 72% for the NBPC30 panel. False positive and false negative rates were higher for the NBPC30 panel. CONCLUSION: Our data shows that the NBC41 panel is superior to the NBPC30 panel in rapidly identifying ESBL-producing organisms. Use of the NBPC41 panel decreases the turnaround time by 24 hours, allowing the provider to more accurately apply appropriate antibiotic therapy. Additionally, the NBPC41 panel provides more useful antibiotic susceptibility results compared to the NBPC30. We recommend use of this panel as a primary identification and susceptibility panel for gram-negative organisms.

PCR for rapid diagnosis of acute Q fever at a combat support hospital in Iraq.

Acute Q fever is occasionally seen in U.S. military service members deployed to Iraq. Diagnosis relies on serology, which is not available in the combat zone. Improved diagnostic modalities are needed. We performed a pilot study investigating whether Joint Biological Agent Identification and Diagnostic System (JBAIDS), a ruggedized, deployable polymerase chain reaction (PCR) platform, might be useful in the diagnosis of acute Q fever. Patients presenting to a Combat Support Hospital in Iraq with undifferentiated fever had blood drawn for Q fever PCR and these results were compared with serology. PCR was positive in 6 of 9 patients with acute Q fever by serology and negative in all 9 patients with negative serology. These results suggest that PCR using the JBAIDS platform could be of use in the diagnosis of Q fever in deployed settings. Further research into this modality is warranted.