Increased attention is being given to TB among immigrants as a public health issue in industrialized countries (8), which underscores use of our data in determining how to best augment current TB control programs. Our international evaluation of immigrant screening policies among industrialized OECD countries indicated that although screening for active TB is frequently performed, LTBI screening is less common. Moreover, screening that is performed for active TB and LTBI varies among countries. Our results indicate that heterogeneity exists in screening location, selection criteria for which immigrant subgroups to screen, and screening methods used.

The primary objective of immigrant screening in industrialized countries appears to be to diagnose active TB, either before immigration or soon after arrival in the host country. Although diagnosing and treating infectious TB reduces transmission, data from numerous settings suggest that yields for active TB diagnosed at or around the time of migration are low: 0.35% in recent meta-analyses and lower in UK studies (23–26).

Although most countries in our study screened for active TB, screening was not universal, and countries differed in which immigrants they screened. Among countries that screened for active TB, asylum seekers and refugees were most commonly targeted for screening. Although these groups are at high risk for having TB infection and disease (because of poor social circumstances, inadequate housing, poor nutrition, and stress of migration), and yields and effects from screening are likely to be higher among them (23), they constitute only 2.1% of all immigrants to industrialized OECD countries and are likely to have a smaller role in TB epidemiology (12). However, a limitation of current national surveillance data is that it does not stratify TB cases among foreign-born persons by immigration status, which makes it impossible to know what proportion of TB cases arise from documented versus undocumented or illegal immigrants.

There was evidence of heterogeneity for specific countries of origin and TB incidence in countries of origin that were selected for active TB screening. Immigrants from countries with high incidence of TB were generally targeted. However, this targeting was partly modulated because free movement of citizens between EU member states indicated that citizens of certain EU nations with a high incidence of TB (particularly where countries based the decision to screen solely on country of origin) were not eligible to be targets for screening when migrating within the EU, although they would be targeted when migrating to countries (mainly non-EU) that based screening policy on TB incidence. In those industrialized countries that used TB incidence as the selection criteria, screening was performed at incidence thresholds from >15 cases/100,000 to >100 cases/100,000.

It is unclear why countries had such different policies although setting the threshold at a higher level may have increased the yield of screening. The specific immigrant subpopulations targeted (either by country of origin or TB incidence in country of origin) may reflect unique migration patterns to each OECD country (5), which may stem from colonial, historic, or linguistic links, financial resources, the current health care system, and infrastructure to deal with immigrants. A possible limitation of current screening protocols is that they may not target immigrants from regions with a high incidence of TB who arrive in industrialized, low-incidence settings, acquire citizenship, and then move to a country with a low incidence of TB (although this group might be small).

Similar variation was observed in screening tools used to diagnose active TB. Younger children were often screened by clinical examination with or without a TST, although making a diagnosis of active TB in children is often difficult when based on such limited evidence (27). Adults and older children were usually screened by chest radiograph, although the lower age limit at which chest radiographs were permissible varied from birth to 18 years of age. The wide range likely reflects reluctance to unnecessarily expose children to radiation and different, more adult-like patterns of pulmonary disease seen in older children (28).

The prevalence of active TB at entry is small and imported active disease that is detectable among immigrants arriving in their country of destination is not driving the increasing disease incidence seen in foreign-born persons in industrialized OECD countries (24). Moreover, because epidemiologic data suggest a high and increasing proportion of extrapulmonary TB in foreign-born persons, chest radiographs would play a limited role in diagnosis (29,30). This finding would limit screening systems that many industrialized countries currently use for adults. The UK Health Protection Agency has reviewed port health and recommended urgent review of continued use of chest radiography as the initial diagnostic test for new entrants (currently underway) (26).

In contrast, TB epidemiology in OECD countries and molecular typing data indicate that reactivation of imported LTBI in the first few years after immigration is driving the increase in TB cases among foreign-born persons (3). Therefore, although screening for active TB is needed, without commensurate targeting of LTBI, screening is unlikely to control TB at a population level. We found that only half of industrialized countries screened immigrants for LTBI, and refugees/asylum seekers were most commonly targeted for screening. This finding indicates that screening legal immigrants for LTBI remains a low-priority TB control measure in industrialized countries, a potential gap that needs to be urgently addressed.

Among countries that screen for LTBI, there was heterogeneity in which immigrant subgroups were screened. For age, children and young adults were most commonly targeted because these groups have the highest risk for progression to active TB and are most likely to benefit from chemoprophylaxis. However, 47% of countries screened all age groups for LTBI, which suggests that in certain countries, older immigrants are given chemoprophylaxis, despite often-cited concerns about hepatotoxicity (31).

Similar variability was seen in which countries of origin of immigrants were targeted for screening. Among industrialized countries that selected immigrants on the basis of TB incidence in the country of origin, the TB incidence screening threshold ranged from >20 cases/100,000 to >500 cases/100,000. This wide variation likely reflects uncertainty about the optimal threshold at which to screen. Setting the incidence threshold too low would result in large numbers of immigrants needing to be screened. Thus, a low threshold would increase costs and likely overwhelm TB screening services, although many immigrants from lower-incidence countries (who have a low prevalence of TB) often do not contribute to TB incidence in industrialized countries (32). In contrast, if the incidence screening threshold is set too high, few immigrants would be screened, which means that a large proportion of the immigrant population that has LTBI, and subsequently converts to active TB, would be missed (32).

The most cost-effective policy option is likely to be to target at an intermediate incidence that balances, most cost-effectively, the numbers of immigrants being screened (and therefore associated costs) against prevalence of LTBI in the immigrant population (33). However, in many OECD countries, making cost-effective policy decisions about immigrant screening for LTBI is hampered by gaps in evidence in several areas, including which immigrant groups to screen (depending on TB incidence/country of origin), which screening methods to use, and which location is best for screening. This policy may partly explain variability in screening models adopted by OECD countries. These gaps could be appropriately addressed by obtaining prospective, multicenter data on prevalence of LTBI in immigrants and assessing performance of screening tools and outcomes of screening in different locations. This policy would enable investigators to calculate yields and relative cost-effectiveness of screening at different incidence thresholds (as was conducted recently in the United Kingdom [33]), for different screening tools and in different locations, thereby enabling countries to formulate country-specific, evidence-based, immigrant screening policies.

LTBI screening methods also varied widely. The most commonly used screening method was TST. Although TST is widely used and inexpensive, it has poor specificity in Mycobacterium bovis BCG–vaccinated populations (e.g., immigrants arriving in industrialized countries), poor sensitivity in immunocompromised persons, and logistic drawbacks, including the need for a return visit and trained staff (34). Although data suggest that IGRAs have higher specificity and sensitivity than TST (34), their use was limited to 40% of industrialized countries as a confirmatory test for a positive TST result and increasingly as a single-step test to replace TST. This finding may reflect recent evidence that suggests that IGRAs are cost-effective and, if results are positive, can predict progression to active TB (35,36). However, the predictive power of IGRA for progression to active TB does not appear to be higher than that of TST (37). Empirical data are needed for relative performance of these tests in immigrant populations so that contemporary health economic analyses can conclude which screening modality is most cost-effective. Given the pivotal need for predictive power in improving cost-effectiveness of testing for LTBI (33), a more powerfully prognostic test would transform the cost-benefit equation for LTBI screening.

A major factor when considering the potential effect of screening for and treating LTBI is that suboptimal completion rates for chemoprophylactic regimens adversely affect efficacy of screening programs, thereby underscoring the need for adopting a patient-centered approach and new, faster-acting, drugs for LTBI (38). Given these potential drawbacks, an alternative approach, depending on patient preference and risk perception, could be to follow-up persons with LTBI for clinical signs over a defined period to rapidly identify and treat those with infections that become active. This approach is used in parts of the United Kingdom and the Netherlands (39).

Our study builds on previous research, which focused on fewer industrialized countries (40) and was conducted some years ago. However, it failed to capture recent changes in guidance (40), did not specifically focus on LTBI, and failed to identify the critical elements of immigrant screening programs, such as which immigrants were selected for screening (10,40).

Our study had several limitations. Information was gathered through a questionnaire with potential for recall/responder bias, although this limitation was minimized by clarifying ambiguous responses of responders or cross-referencing against national guidelines. In addition, our study only captured what screening is currently recommended and thus presents an idealized situation of how screening should be conducted, which may be different from actual practice at the local level (14). Only a detailed assessment of national practice can determine the extent to which national guidance is followed.

TB in industrialized countries primarily occurs in foreign-born persons. Current immigrant screening policies in these countries focus primarily on identifying active TB. Although the contribution of active TB at the time of immigration is crucial, data from 2 large contemporary meta-analyses suggest that the prevalence of active disease in immigrants arriving from countries with a high incidence of TB remains relatively low (0.35%) (23,24), making cost-effectiveness and value of the current screening strategies uncertain. In contrast, epidemiologic data suggest that LTBI reactivation in immigrants plays a central role in determining national TB incidence. However, LTBI screening is paradoxically limited, and there is no consensus on which immigrants to screen and how to screen.

Addressing these issues is critical to effective TB control in industrialized countries, as is identification and treatment of persons with LTBI, and where control measures should be targeted while remaining vigilant about timely diagnosis and treatment for active disease. To address this problem effectively, robust evidence-based data are urgently needed to develop affordable, effective, and cost-effective policies on which immigrant subgroups to screen (33). Such policies will need to be developed in the context of nation-specific economic considerations, including resource availability and the funds policy makers are willing to spend to control the incidence of active TB.