Immigration screening for latent tuberculosis infection

In Australia, 1222 cases of tuberculosis (TB) were notified in 2011, which represents an annual incidence of six cases per 100 000 population.1 Despite this relatively low incidence by global standards, TB disease continues to cause significant morbidity and mortality, and has a substantial impact on the health and wellbeing of affected individuals and communities.2 In addition to the direct clinical impact, effective management of TB imposes a substantial burden on health care systems and public health programs. Opportunities to reduce TB incidence further in Australia, therefore, would be welcome and should be actively pursued.

Over the past decade, 80%–90% of people who developed TB in Australia were born overseas, with by far the most common clinical pathway to presentation being reactivation of previously latent TB infection (LTBI).3 People migrating to Australia from countries with high TB incidence are at significant risk of developing TB disease, even decades after arrival.4 In 2012, the National Tuberculosis Advisory Committee highlighted the importance of migrants in their strategic plan for control of TB in Australia, identifying overseas-born people in general, and overseas-born students in particular, as priority populations in the plan to reduce TB risk.5 Effective therapy for preventing reactivation is available, but most people who have LTBI have not been diagnosed and are unaware of their risk of developing active TB disease. Practical approaches to diagnosing LTBI among groups who are at high risk of TB disease are required, particularly close to the time of arrival in Australia because this is when diagnosis of LTBI would be most effective in preventing subsequent disease. While a variety of different strategies might accomplish this aim, perhaps the most efficient would be incorporating a screening program for LTBI into the existing immigration process.

Currently, TB screening in immigrants consists of a chest x-ray and a clinical examination before entry, to identify those with active disease. This program, combined with postmigration follow-up (the TB Health Undertaking) is effective in identifying migrants who have active TB infection.6 However, no testing for LTBI — with tests such as the tuberculin skin test or the interferon-γ release assay (eg, the QuantiFERON-TB Gold In-Tube assay [Cellestis], which is in use in Australia) — is performed routinely, apart from the testing done in accordance with recommendations to screen refugees and asylum seekers. Thus, the opportunity to systematically identify those at highest risk of progression to active TB is missed, as is the chance to intervene and prevent TB disease.

Arguably, the most appropriate approach to identifying LTBI in immigrants would be a requirement for LTBI testing to be performed on those arriving from countries with a high incidence of tuberculosis, followed by provision of effective LTBI therapy after arrival. For such a strategy to be justifiable, it should screen immigrants with an appropriately large risk of LTBI, using a test with high specificity, and positive test results should not be used to restrict migration.7 Data from LTBI screening programs in the United Kingdom suggest that the use of an interferon-γ release assay for screening immigrants from high-incidence countries would have a high yield of positive results — a positive test result is seen in 20% and 28% of migrants from the Indian subcontinent and sub-Saharan Africa, respectively.8 These programs are cost-effective when used to screen those younger than 35 years from countries with TB incidence of more than 40 cases per 100 000 population per year, with optimal efficiency for country thresholds of about 150 cases per 100 000 population per year.8 While an optimal threshold for the Australian context remains to be established, it is likely to be broadly comparable with the UK experience, suggesting that an efficient and cost-effective immigration screening program is a realistic consideration.

TB rates in Australia are likely to continue to rise due to the ongoing arrival of migrants with LTBI. While international efforts to control TB disease in high-incidence countries are critical for reducing transmission, prevention of LTBI reactivation is very important in terms of eradicating TB as a global public health issue. An immigration screening program for LTBI would be an effective and practical way to improve the health of new Australians through prevention of TB, reduce TB incidence and risk of secondary transmission in the Australian community, and further strengthen TB control programs in the Asia–Pacific region.