Role of an interferon-gamma based assay (T-SPOT®.TB) for the diagnosis of tuberculosis in routine clinical practice

Abstract number: 1733_1501

Santos J., Cordeiro M., Hanscheid T., Valadas E., Antunes F.

Objectives: Diagnosis of tuberculosis (TB) can be difficult and is often fraught with long delays, which makes the search for new diagnostic methods very important. This issue is even more relevant in HIV infected patients. We evaluated the role of a new commercial ELISPOT for the diagnosis of TB in routine clinical practice.

Methods: T-SPOT.TB was performed in consecutive patients admitted to the Department of Infectious Diseases at a large teaching Hospital in Lisbon, in 2006. Twenty healthcare workers (HCW), from the Departments of Infectious Diseases and Microbiology, agree to participate as control group. PBMCs, obtained using a Ficoll gradient, were incubated overnight in a cell culture containing ESAT-6 and CFP-10. The assay detects individual effector T cells through their secretion of interferon-gama which results in a spot. A sample was considered positive if a well showed at least 6 spots more than the negative control well.

Results: Patients (n = 79) were male, and all were BCG vaccinated. Mean age was 40 years and 55 (70%) were HIV infected. Fourteen patients (22.8%) had TB, latter confirmed by culture, and most were HIV infected (n = 12, 85.7%). Of those, ELISPOT was positive in 11 patients (78.6%), negative in two (14.3%), and indeterminate in one (7.1%). From the remaining 55 patients admitted for other infectious cause, 13 (23.6%) also had a positive ELISPOT. All 20 HCW had a negative result.

Conclusion: ELISPOT was positive in almost 80% of all TB cases, even in a population with a very high rate of HIV infection and severe imunodepression. As T-SPOT.TB uses ESAT-6 and CFP-10, Mycobacteriumtuberculosis complex specific antigens, these results were expected in TB cases. Over the last few years, several studies have showed that this test might have an important role on the diagnosis of latent infection (LTBI). As Portugal has the highest incidence of TB in Western Europe (~40/100.000), one would expect to find a high prevalence of latent infection. ELISPOT was positive in ~1/3 of all patients with other diagnosis, results that support the role of this test in the diagnosis of LTBI. Therefore, T-SPOT.TB is highly likely to become a useful and sensitive assay for the diagnosis of TB in routine clinical practice, as well as to identify individual with LTBI. The capacity of this test to identify patients that might have a worse response to treatment, as well as those individuals that can progress from infection to disease, is still to be proven.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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