The average number of latent TB infection (LTBI) treatments needed to prevent one incident TB by result of QuantiFERON TB Gold (n=44 875)
| No LTBI treatment | LTBI treatment | NNT (95% CI) | |||
| n | TB | n | TB | ||
| Total study population | 42 433 | 257 | 2442 | 4 | |
| Positive, total* | 7747 | 219 | 2131 | 4 | 38 (35 to 41) |
| Low positive | 1809 | 17 | 357 | 0 | 106 (102 to 112) |
| Medium positive | 2084 | 46 | 586 | 3 | 59 (44 to 90) |
| High positive | 3854 | 156 | 1188 | 1 | 25 (24 to 27) |
| Negative | 33 835 | 33 | 293 | 0 | 1025 (1014 to 1036) |
| Inconclusive | 851 | 5 | 18 | 0 | 170 (159 to 182) |
| Foreign-born, total | |||||
| Positive, total* | 6580 | 164 | 1726 | 4 | 34 (32 to 38) |
| Low positive | 1252 | 13 | 222 | 0 | 78 (74 to 83) |
| Medium positive | 1735 | 36 | 441 | 3 | 54 (38 to 92) |
| High positive | 3593 | 115 | 1063 | 1 | 25 (24 to 27) |
| Negative | 10 760 | 14 | 111 | 0 | 598 (587 to 609) |
| Inconclusive | 229 | 5 | 12 | 0 | 46 (41 to 53) |
| Norwegian-born, total | |||||
| Positive, total* | 1167 | 12 | 405 | 0 | 90 (85 to 95) |
| Low positive | 557 | 1 | 135 | 0 | 557 (514 to 607) |
| Medium positive | 349 | 2 | 145 | 0 | 175 (158 to 195) |
| High positive | 261 | 9 | 125 | 0 | 26 (23 to 30) |
| Negative | 23 075 | 10 | 182 | 0 | 1538 (1519 to 1558) |
| Inconclusive | 622 | 0 | 6 | 0 | – |
*Low positive, IFN-γ 0.35 to <1.0; medium positive, IFN-γ 1.0 to <4.0; high positive, IFN-γ>4.0 IU/mL.
IFN-γ , interferon-γ; NNT, numbers needed to treat.