Two-year tuberculosis risk in untreated adult contact subgroups and indices of performance with QFT for screening
| Subgroups of contact exposure | ||||
|---|---|---|---|---|
| All adult contacts | Non-smear positive | Smear positive (all) | Smear positive (≥36 years) | |
| 2-year risk [cases/cohort size]† | ||||
| All untreated | 2.5 (1.7 to 3.2) [39/1669] | 1.3 (0.8 to 2.1) [16/1263] | 6.2 (4.6 to 8.1) [23/406] | 6.5 (3.4 to 10.5) [12/211] |
| QFT positive | 13.4 (7.7 to 21.1) [14/112] | 13.7 (4.6 to 31.1) [4/32] | 13.4 (6.8 to 22.8) [10/80] | 8.9 (3.3 to 19.1) [5/62] |
| QFT negative | 1.1 (0.4 to 2.3) [6/601] | 0.3 (0.01 to 1.7) [1/371] | 2.4 (0.8 to 5.4) [5/230] | 3.4 (0.8 to 9.4) [3/98] |
| Rate ratio (QFT pos: All)‡ | 4.9 (2.7 to 8.7) p<0.001 | 8.9 (3.1 to 25) p<0.001 | 2.1 (1.02 to 4.2) p=0.041 | 1.4* (0.5 to 3.9) p=0.503 |
| Prevalence QFT positive/% | 26.3 (23.2 to 29.0) | 19.5 (16.0 to 23.0) | 34.5 (29.6 to 39.4) | 39.1 (31.5 to 46.7) |
| Sensitivity§ | 70.0 (45.7 to 88.1) | 80.0 (28.4 to 99.5) | 66.7 (38.4 to 88.2) | 62.5 (30.6 to 86.3) |
| Specificity§ | 85.9 (83.0 to 88.4) | 93.0 (89.9 to 95.3) | 76.3 (71.0 to 81.0) | 62.5 (54.6 to 69.8) |
| PPV§ | 12.5 (7.0 to 20.1) | 12.5 (3.5 to 29.0) | 12.5 (6.2 to 21.8) | 8.1 (2.7 to 17.8) |
| NPV§ | 99 (97.8 to 99.6) | 99.7 (98.5 to 99.9) | 97·8 (95.0 to 99.3) | 96.9 (91.3 to 99.4) |
| LR+ | 4.95 (3.5 to 7.0) | 11.4 (6.5 to 20.0) | 2·8 (1.9 to 4.2) | 1.7* (0.94 to 3.0) |
| LR− | 0.35 (0.18 to 0.68) | 0.22* (0.04 to 1.2) | 0.44 (0.21 to 0.90) | 0.6* (0.24 to 1.5) |
| Number needed to screen | 35.0 (21.5 to 93.1) | 41.5 (20.0 to 432) | 40.0* (−18.3 to 217) | 105* (−39.6 to 22.5) |
| Number needed to treat | 6.8 (3.8 to 9.9) | 6.5 (3.6 to 33.8) | 7.0 (4.5 to 15.0) | Not applicable |
All figures in parentheses are 95% CI of the mean unless stated otherwise.
*p Value >0.05.
†Two-year risk is presented as a cumulative percentage (95% CI). Figures in square brackets refer to the actual numbers of cases and the size of the cohort from which they arise, for each subgroup.
‡For rate ratio calculations, all contacts refers to the group selected for longitudinal analysis that was adherent with the screening algorithm (see Methods section).
§PPV, NPV, sensitivity and specificity are all presented as % values.
LR−, likelihood ratio associated with a negative QFT result; LR+, likelihood ratio associated with a positive QFT result; NPV, negative predictive value; PPV, positive predictive value; QFT, QuantiFERON tuberculosis Gold-In Tube.