Immigrant screening for latent tuberculosis infection: numbers needed to test and treat, a Norwegian population-based cohort study

Abstract

ObjectivesTo estimate the number needed to screen (NNS) and the number needed to treat (NNT) to prevent one tuberculosis (TB) case in the Norwegian immigrant latent tuberculosis infection (LTBI) screening programme and to explore the effect of delay of LTBI treatment initiation.DesignPopulation-based, prospective cohort study.ParticipantsImmigrants to Norway.OutcomeIncident TB.MethodsWe obtained aggregated data on immigration to Norway in 2008–2011 and used data from the Norwegian Surveillance System for Infectious Diseases to assess the number of TB cases arising in this cohort within 5 years after arrival. We calculated the average NNS and NNT for immigrants from the top 10 source countries for TB in Norway and by estimated TB incidence rates in source countries. We explored the sensitivity of these estimates with regard to test performance, treatment efficacy and treatment adherence using an extreme value approach, and assessed the effects of emigration, time to TB diagnosis (to define incident TB) and intervention timing.ResultsNNS and NNT were overall high, with substantial variation. NNT showed numerically stronger negative correlation with TB notification rate in Norway (−0.75 [95% CI −1.00 to −0.44]) than with the WHO incidence rate (IR) (−0.32 [95% CI −0.93 to 0.29]). NNT was affected substantially by emigration and the definition of incident TB. Estimates were lowest for Somali (NNS 99 [70–150], NNT 27 [19–41]) and highest for Thai immigrants (NNS 585 [413–887], NNT 111 [79–116]). Implementing LTBI treatment in immigrants sooner after arrival may improve the effectiveness of the programme.ConclusionUsing TB notifications in Norway, rather than IR in source countries, would improve targeting of immigrants for LTBI management. However, the overall high NNT is a concern and challenges the scale-up of preventive LTBI treatment for significant public health impact. Better data are urgently needed to monitor and evaluate NNS and NNT in countries implementing LTBI screening.

Effectiveness of nationwide programmatic testing and treatment for latent tuberculosis infection in migrants in England: a retrospective, population-based cohort study

“…We provide a programmatic NNT estimate of relevance for national and international policy makers. Our estimates of NNT were similar to other studies in the UK and Norway, 35 , 36 and lower than modelling-based estimates for the USA. 37 , 38 The high NNT raises important issues because LTBI treatment might be given with no benefit, while exposing individuals to potential adverse events, even if this risk is low.…”

Factors Associated with Treatment Prescription to Pulmonary Tuberculosis Contacts in Catalonia (2019–2021): A Population-Based Epidemiological Study

“…LTBI treatment prescription was also associated with migrant contacts aged ≥6 years. LTBI treatment decisions regarding migrants from countries with high TB incidence continues to be challenging, as the rate of active TB development over the long term appears to be higher in migrants with detected TB infection [ 20 , 21 ]. While Tang et al [ 19 ] reported no association between migrant status and LTBI treatment prescription, our results suggesting that Catalan physicians take migrant status into account when prescribing treatment corroborates findings for a study carried out among new migrants in Montreal [ 22 ].…”

Cost-effectiveness of IGRA/QFT-Plus for TB screening of migrants in Oman

“…et al, 2017). A study from Norway estimated the number needed to treat (NNT) to prevent one case of active TB (Winje et al 2019); the number varied from 17 for migrants from Somalia to 111 for migrants from Thailand.…”

“…Another option is to limit treatment to persons with a strongly positive IGRA result, defined as >4 IU/ml. These persons are at high risk of developing active TB within the next 2 years (Andrews et al, 2017;Winje et al, 2019). Cost-effectiveness would increase if focus was placed on this group.…”