Respiratory Care |

Performance of Tuberculin Skin Test and Quantiferon-TB-Gold in Tube Assay (QFG-IT) in Active and Latent Tuberculosis in High Burden Settings FREE TO VIEW

Maha Ghanem; Hebat Allah Rashed
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Assiut University Hospital, Assiut, Egypt

Chest. 2014;146(4_MeetingAbstracts):928A. doi:10.1378/chest.1992664
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SESSION TITLE: Respiratory Infections

SESSION TYPE: Original Investigation Slide

PRESENTED ON: Tuesday, October 28, 2014 at 11:00 AM - 12:15 PM

PURPOSE: To evaluate the performance of QFG-IT in active and latent tuberculosis infection (LTBI) in high TB burden setting in low-middle income country (LMIC).

METHODS: In a cross-sectional study, we compared the TST and QFG-IT assay in a cohort of 210 participants classified into three groups; Group I investigated for LTBI and included 74 health care workers (HCWs) with known close contact to active TB cases, Group II; 83 patients with known active TB disease, Group III; 53 apparently healthy control subjects.

RESULTS: Of 210 participants in the 3 groups, 117 (55.7%) had a TST result of ≥ 10 mm; 42 (20%) of them had indurations ≥15 mm. QFG-IT was positive in 69 (32.9%) of the cohort, in 23 (31.1%) of 74 HCWs investigated for LTBI and in 40 (48.2 %) in patients clinically suspected to be tuberculous; 63 (75.9%) of them proved to have active TB. Among healthy control, 6 (11.3%) were positive, meanwhile 21 (10.0%) from the enrolled cohort had indeterminate QFG-IT results. In patients investigated for active TB, QFG-IT was positive in 16/19 cases (84.2%) of PTB, and in 22/39 cases (56.4%) of EPTB. Sensitivity, specificity, positive and negative predictive values of QFG-IT assay were 65.62%, 80%, 95%, and 28.6%, meanwhile they were 90.57%, 50%, 90.57% and 33.33% for TST, respectively. Positive QFG-IT tests were associated with older age, female gender, BCG vaccination and longer duration of work in health care setting. Overall agreement between the 2 tests was moderate (75.66%, κ 0.526) and in healthy control was fair 78.13% (κ 0.201). Also, there were moderate agreements between the two tests among HCWs investigated for LTBI and patients investigated for active TB (76.47%, κ 0.570), and (77.49%, κ 0.511), respectively.

CONCLUSIONS: QFG-IT is more specific in the diagnosis of latent and active TB infections. There was moderate agreement between TST and QFG-IT test in diagnosing LTBI and active TB infection in high burden setting.

CLINICAL IMPLICATIONS: Despite higher specificity of QFG-IT test, TST remains a cost effective test in LMICs with limited budget for use of IGRA tests as screening tool in national control programs. However, QFG-IT in conjunction with TST improves the diagnostic yield, can help identifying at-risk groups and reduce the indication of preventive chemotherapy in high burden settings.

DISCLOSURE: The following authors have nothing to disclose: Maha Ghanem, Hebat Allah Rashed

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