Use of QuantiFERON-TB Gold In-tube assay in screening for neutralizing anti-interferon-γ autoantibodies in patients with disseminated nontuberculous mycobacterial infection

OBJECTIVE

Anti-interferon- γ (IFN-γ) autoantibodies (anti-IFN-γ Abs) have been increasingly recognized as an important cause of disseminated nontuberculous mycobacterial (DNTM) infection, and identification of this immunodeficiency impacts clinical management. However, the protean disease manifestations and inaccessibility to diagnostic tests in clinical settings hamper its early diagnosis. Here, we sought to determine whether QuantiFERON-TB Gold In-tube (QFT-GIT), a commercialized IFN-γ release assay, could be used to screen for neutralizing anti-IFN-γ Abs among previously healthy adults with DNTM infection.

METHODS

Non-HIV patients with DNTM infection were prospectively enrolled for the QFT-GIT assays. We measured their plasma concentration of anti-IFN-γ Abs and their neutralizing capacity through enzyme-linked immunosorbent assay and flow cytometry. We then analysed the correlation between QFT-GIT results and the presence of neutralizing anti-IFN-γ Abs among patients with and without previously recognized immunosuppression, respectively.

RESULTS

Irrespective of the autoantibody concentration or disease activity, all patients with neutralizing anti-IFN-γ Abs (100%, 30/30) had indeterminate QFT-GIT results because of extremely low or undetectable IFN-γ levels in the mitogen tubes. None of the four DNTM patients who were previously healthy and tested negative of anti-IFN-γ Abs had an indeterminate QFT-GIT result, and their IFN-γ levels in the mitogen tube were significantly higher than those of the patients with anti-IFN-γ Abs (8.28 IU/mL vs. 0.05 IU/mL, p 0.001).

CONCLUSION

An indeterminate QFT-GIT result because of undetectable or extremely low IFN-γ level in the mitogen tube suggests the presence of neutralizing anti-IFN-γ Abs in a previously healthy patient with DNTM infection.

Incidence and species distribution of candidaemia in Asia: a laboratory-based surveillance study

The epidemiology of candidaemia varies between hospitals and geographic regions. Although there are many studies from Asia, a large-scale cross-sectional study across Asia has not been performed. We conducted a 12-month, laboratory-based surveillance of candidaemia at 25 hospitals from China, Hong Kong, India, Singapore, Taiwan and Thailand. The incidence and species distribution of candidaemia were determined. There were 1601 episodes of candidaemia among 1.2 million discharges. The overall incidence was 1.22 episodes per 1000 discharges and varied among the hospitals (range 0.16-4.53 per 1000 discharges) and countries (range 0.25-2.93 per 1000 discharges). The number of Candida blood isolates and the total number of fungal isolates were highly correlated among the six countries (R² = 0.87) and 25 hospitals (R² = 0.77). There was a moderate correlation between incidence of candidaemia and the intensive care unit (ICU)/total bed ratio (R² = 0.47), although ICUs contributed to only 23% of candidaemia cases. Of 1910 blood isolates evaluated, Candida albicans was most frequently isolated (41.3%), followed by Candida tropicalis (25.4%), Candida glabrata (13.9%) and Candida parapsilosis (12.1%). The proportion of C. tropicalis among blood isolates was higher in haemato-oncology wards than others wards (33.7% versus 24.5%, p 0.0058) and was more likely to be isolated from tropical countries than other Asian countries (46.2% versus 18.9%, p 0.04). In conclusion, the ICU settings contribute, at least in part, to the incidence variation among hospitals. The species distribution is different from Western countries. Both geographic and healthcare factors contribute to the variation of species distribution.

Risk factors and outcomes of Escherichia coli bacteremia caused by strains that produce CTX-M or non-CTX-M extended-spectrum-beta-lactamases

To determine whether there are differences in risk factors and outcomes among patients with E. coli bacteremia caused by strains that produce CTX-M or non-CTX-M extended-spectrum beta-lactamases. From 1 July 2005 to 30 June 2007, patients with positive blood culture of extended-spectrum β-lactamases (ESBL)-producing E. coli were reviewed. Sixty patients with ESBL-producing E. coli bacteremia were identified. These included 41 (68.3%) isolates with CTX-M β-lactamases. CTX-M-14 accounted for 31 (75.6%) and CTX-M-3 for 9 (22.0%) of the 41 CTX-M isolates. Patients with CTX-M strains were less likely, by univariate analysis, to have significant risk factors for infection including age ≥ 65 years, chronic renal insufficiency, ICU stay at bacteremia onset, central venous catheter use and mechanical ventilation. Multivariate analysis revealed that chronic renal failure and ICU stay were independent predictors. Antibiograms were similar for CTX-M and non-CTX-M producers except that CTX-M strains were significantly more susceptible to cefmetazole (92.7 vs 36.8%, p < 0.0001). The overall mortality and length of hospitalization were not significantly different between the two groups. E. coli with CTX-M β-lactamases was more likely than non-CTX-M strains to invade non-compromised patients. There were no differences in clinical outcomes between the two groups.