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Table 3 Screening recommendations in low-incidence countries based on TB incidence, positive predictive value of IGRAs and TST for progression to active TB disease, and number needed to screen

From: Recommendations for the screening of paediatric latent tuberculosis infection in indigenous communities: a systematic review of screening strategies among high-risk groups in low-incidence countries

Country or Region Risk Sub-group Studied Screening Tool 2015 National TB Incidence (reported cases/million population/year) [58] PPV a for Progression to Active Disease NNT b or NNS c Screening Tool Recommendations Screening Strategy Recommendations
Canada Indigenous individuals [24] d TST 45.55 NR NNS: 5.3 Use of the TST in the paediatric population, although IGRAs may be preferable in areas where BCG vaccination persists
[26, 27]
Location-based screening in Indigenous communities with > 5 TB cases in the past 5 years [24]
Individuals in long-term care facilitiesd [59] TST   NR 1410
Australia Immigrant/refugee children or child contacts of TB cases TST & IGRAs 52.25 NR NR Although prior studies indicate potentially poorer sensitivity of IGRAs compared to the TST, [38, 43]the basis of this conclusion in the absence of a gold standard diagnostic tool is unclear, and a more recent study suggests poorer sensitivity of the TST compared to IGRAs for the detection of LTBI, based on a prospective follow-up of study subjects. [44]  
Italy Immigrant children and child contacts of TB cases TST & IGRAs 62.82 NR NR Use of IGRAs recommended in BCG-vaccinated paediatric populations [56]  
Spain Immigrant children [47] QFT-GIT & TST 91.12 NR NR Use of IGRAs is preferential in low-incidence settings to prevent unnecessary prophylactic treatment Risk-based screening: contacts of TB cases and undocumented immigrant children [46, 47]
Contacts of TB cases [46] QFT-GIT & TST   NR NR
United Kingdom [33] Immigrant children from low-incidence countries (< 150/100,000) NR 96.00 NR NNS: 5291 IGRAs are more cost-effective in low-incidence countries [37] Risk-factor-based screening: immigrants from high-incidence countries [33,34,35]
Immigrant children from high-incidence countries (> 500/100,000) NR   NR 88
United States Immigrants d [60] TST 29.66 NR NNS: 150 IGRAs are a better predictor of progression to active disease in paediatric populations [40, 41] Risk-factor-based screening: immigration status, malnutrition [31, 32, 36]
Europe d [54] Immune-compromised individuals [61] TST
QFT-GIT
T-SPOT.TB
NA 1.5
0.9
1.3
NNT:
50
80
60
  Targeted screening of close contacts [54]
Contacts of TB cases [62] QFT-GIT
T-SPOT.TB
NA 1.9
0.7
37
37
  1. aPPV = Positive Predictive Value (in this case, the number of individuals progressing to TB disease among those with a positive IGRA result)
  2. bNNT = Number Needed to Treat (in this case, the difference between the number of TB cases developing among individuals testing positive via IGRA in those receiving compared to not receiving prophylactic treatment)
  3. cNNS = Number Needed to Screen (the number of individuals needed to screen in order to prevent one TB case)
  4. dNot in exclusively paediatric populations
  5. NA Not applicable
  6. NR Not reported