Background Notifications for tuberculosis (TB) in the United Kingdom (UK) increased by 30% between 1992 and 2007 with overseas-born migrants accounting for 72% of cases in 2007. Much of this increase is due to the synergy of migration from high-TB burden countries and the reactivation of pre-existing latent TB infection (LTBI). Since 2006, NICE guidance advocates screening for LTBI in all children from countries with a TB incidence >40/100 000 and adults from Sub-Saharan Africa and countries with a TB incidence >500/100 000. The rationale underpinning these guidelines remains unclear particularly as there are little data on the prevalence of LTBI in immigrants to the UK from regions with different TB incidence rates.
Aims To quantify the prevalence of LTBI in immigrants, assess factors associated with IGRA positivity and to determine LTBI yield from current screening thresholds recommended by NICE.
Methods Analysis of data prospectively obtained through IGRA testing (QuantiFERON-Gold/QuantiFERON-Gold-in-tube) of immigrants in three different centres in the UK during 2008–2010. Descriptive analyses were undertaken. Yields at different screening thresholds were calculated. Subsequent univariate and multivariate analyses were undertaken to assess independent factors associated with IGRA positivity; p<0.05 considered significant.
Results In total 915 immigrants were screened during the study period. Median age was 26.8 years (interquartile range 22–33), 50.6% were female and 72.5% had previously been BCG vaccinated. 48.9% and 28.5% of migrants screened originated from the Indian Subcontinent and Sub-Saharan Africa, respectively. Overall 911/915 individuals had determinate IGRA results—199 (21.7%) tested positive and 712 (77.8%) tested negative; 4 (0.4%) individuals had indeterminate results. Multivariate analysis revealed that increasing age (p<0.0001) and increasing TB incidence of country of origin (p=0.0014) were independently associated with IGRA positivity. Applying current NICE guidance resulted in a yield of 76/311 (24.4%) but would miss 61.8% of the immigrant population with LTBI (Abstract S5 Table 1).
Conclusions Immigrants have a high prevalence of LTBI but current NICE guidance detects only 38.2% of new entrants with LTBI. Given the high rates of reactivation of LTBI in new entrants, our findings suggest that consideration should be given to reducing the screening threshold to include those from the Indian Subcontinent (incidence 170/100 000) which would result in 67.8% of all LTBI cases being identified.