Sensitivity Analysis and Potential Uses of a Novel Gamma Interferon Release Assay for Diagnosis of Tuberculosis

Abstract

Sputum smears for acid-fast bacilli (AFB) are the primary methods for diagnosis of tuberculosis (TB) in many countries. The tuberculin skin test (TST) is the primary method for diagnosis of latent TB infection (LTBI) worldwide. The poor sensitivity of the former and the poor specificity of the latter warrant the development of new tests and strategies to enhance diagnostic capabilities. We evaluated the sensitivity of an "in-tube" gamma interferon release assay (IGRA) using TB-specific antigens in comparison to the TST and the sputum smear for AFB in TB cases in South Africa. The sensitivity of the IGRA for TB was considered a surrogate of sensitivity in LTBI. Among 154 patients with a positive culture for Mycobacterium tuberculosis, the sensitivity of the IGRA for the diagnosis of TB varied by clinical subgroup from 64% to 82%, that of the TST varied from 85% to 94%, and that of two sputum smears for AFB varied from 35% to 53%. The sensitivity of the IGRA in human immunodeficiency virus (HIV)-infected TB cases was 81%. HIV-infected TB patients were significantly more likely to have indeterminate IGRA results and produced quantitatively less gamma interferon in response to TB-specific antigens than HIV-negative TB patients. The overall sensitivity of the TST in all TB cases was higher than that of the IGRA (90% versus 76%, respectively). The combined sensitivities of the TST plus IGRA and TST plus a single sputum smear were 96% and 93%, respectively. The TST combined with IGRA or with a single sputum smear may have a role in excluding the diagnosis of TB in some settings.Worldwide, there were 8.8 million new cases of active tuberculosis (TB) and an estimated 1.7 million deaths from TB in 2003 (32). With increased numbers of TB cases, health systems in resource-limited settings face difficulties in coping with the large patient and specimen loads (16). Sputum smear for acidfast bacilli (AFB) (two or three smears) is the primary microbiologic method used for diagnosis of TB in resource-limited settings. Cultures for AFB require more extensive laboratory facilities, and their cost can be prohibitive. However, there is concern regarding this dependence on the sputum smear for AFB due to its limited sensitivity. Human immunodeficiency virus (HIV) coinfection can further complicate TB diagnosis with an atypical clinical picture of pulmonary TB and a higher likelihood of negative sputum smears for AFB (7,8,12,13,25). The tuberculin skin test (TST) is the standard for diagnosis of latent tuberculosis infection (LTBI), is the only test available for that purpose in resource-limited settings, and is sometimes used to aid in the diagnosis of active TB; however, its specificity is limited by cross-reactivity with nontuberculous mycobacteria and BCG vaccine strains of Mycobacterium bovis, and its sensitivity can be affected by malnutrition and immunosuppression (17,27).Because of the efficacy of current therapeutic options, the need is great for affordable and rapid diagnostic methods with high sensitivity and specificity fo...

Sensitivity of C-Tb: a novel RD-1-specific skin test for the diagnosis of tuberculosis infection

“…In contrast, TST sensitivity was ∼89%. Although this appears to be higher than reported in other studies [21], it is in agreement with previous studies from South Africa [22]. The latter is likely due to the high force of infection [23], ongoing T-cell priming by the high prevalence of environmental mycobacteria [24] and previous BCG vaccination [9].…”

Interferon-γ release assays for the diagnosis of latentMycobacterium tuberculosisinfection: a systematic review and meta-analysis

“…Four studies were from intermediate-burden countries (South Korea [55], Lithuania [59], Iran [63] and Turkey [72]) and three studies were from high-burden countries (India [56], South Africa [61] and Vietnam [65]). Seven studies were based solely on paediatric cohorts [39,51,54,59,73,75] and three studies [47,57,61] included children in the study population.…”

Diagnosis of tuberculosis infection using interferon-γ-based assays

“…58 In 4 studies that compared performance of QFT-IT in HIV-infected and non-infected adults with active TB, mean sensitivity was 64% in HIV-infected patients and 79% in non-HIV-infected patients. [59][60][61][62] Although the overall sensitivity of T-SPOT.TB is higher than that of QFT-IT in otherwise healthy people, data from head-to-head comparisons in HIV-infected patients are scarce. 60,63,64 In three studies, covering a total of 39 patients with culture-confirmed TB, QFT-IT and T-SPOT.TB detected 74% and 82% of cases respectively.…”