Controlling Tuberculosis among Foreign Born within Industrialized Countries
Expensive Band-Aids

Dick Menzies, M.D.

Montreal Chest Institute, McGill University, Montreal, Canada

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Of all active cases of tuberculosis (TB) diagnosed in industrialized countries, the proportion among the foreign-born population has rapidly increased over the past 20 yr. Cases among the foreign born accounted for over 60% of the total reported in many European countries (1) and Canada (2) in 1997, and 43% of cases in the United States in 1999 (3). This is because of a steady decline in cases among the native-born populations of these countries, and large scale immigration from countries with a high incidence of TB. Control of tuberculosis in the foreign-born populations within industrialized countries has emphasized screening of permanent residents at the time of arrival with passive diagnosis thereafter. The article in this issue by Weis and colleagues (pp. 953-957) (4) demonstrates the limitations of this approach, and provides support for a global strategy.

Between January 1, 1998 and December 1, 2000, foreign-born individuals accounted for 114 (42%) of the 267 reported culture positive cases of active tuberculosis in Tarrant county, Texas. Of these, 28 occurred among individuals without any visa, and 19 in individuals with short-term student, work, or visitor visas. These two groups, who were not screened, accounted for 41% of all foreign-born cases and 16% of all TB cases reported during the study period. Costs for care were high, particularly for those with short-term visas, largely because 32% were HIV positive with advanced immune suppression, and 16% had MDR-TB. Weis and colleagues suggest that screening should be considered for applicants for short-term visas (4).

Radiographic screening for active TB at or before entry has been evaluated in a number of countries. Prevalence of active TB was only 0.1-0.2% of most immigrant populations (5), although it was higher among refugees (8). Periodic radiographic screening (e.g., annually) has never been attempted for immigrants, largely because such programs are very expensive, have low yield, and detect only a small fraction of all smear positive active cases (9). Radiographic screening could have greater benefit if those identified during screening to have inactive TB are prescribed, and complete, preventive therapy. However, when evaluated under program conditions, this approach proved more expensive, less effective, and hence much less cost effective than contact investigation (7).

The benefits and cost effectiveness of immigration screening are reduced for a number of reasons. The most important limitation is that the currently available screening toolschest radiography and tuberculin testingare insensitive and nonspecific. Chest radiography will identify a higher risk subgroup, but is complex, expensive, and has poor reproducibility (9). The unit cost of tuberculin testing is less, but false positive reactions are common, and the majority of infected persons identified have very low risk of disease (10). Preventive therapy at present is lengthy, expensive because of the need for close medical monitoring, and potentially toxic. As a result, physicians and patients often do not follow treatment recommendations, further reducing any benefit of screening (7).

If these problems could be overcome, would it be feasible to screen the nonpermanent migrants? The U.S. department of Justice estimated that in 1998, 435,000 refugees and immigrants legally took up permanent residence in the United States; these individuals were screened for tuberculosis. Another 275,000 persons took up residence but without documentation, that is, illegally; this group obviously was not screened. In the same year, approximately 30 million visitors entered without visas, and another 30.2 million entered with temporary work, study, or visitor visas. Even if the costs of screening those with temporary visas were borne entirely by applicants, this screening would impoverish the migrants, and result in a huge net cash flow into curative services overseas. As well screening 30 million applicants each year would represent an enormous administrative burden for processing and reviewing medical files, particularly for complex cases and appropriate referral of individuals who required follow-up. This would also result in a huge increase in the number of individuals referred to local health departments after arrival. Because any benefit of screening will be achieved only if these individuals are properly followed, these health departments would require substantial additional resources.

A limitation of screening immigrants at the time of initial entry is that these individuals often return for prolonged periods to their country of origin. Weis and colleagues report that 23% of all foreign-born individuals had traveled to TB endemic areas within the preceding 2 yrfor a median of 42 d (4). This travel has been identified as an important risk factor for TB infection (11), and disease (12), raising the question of whether such individuals should be screened at the time of each reentry.

A further limitation of concentrating TB control efforts within industrialized countries is demonstrated by the differences in HIV sero-prevalence and drug resistance among the three foreign-born subgroups in Tarrant county (4). Given the results of statistical testing, it is unlikely these were the result of chance. Rather this may reflect self-selection by individuals who needed TB treatmentwhich is often unavailable in developing countries. Individuals who would otherwise die of untreated TB in their own country may take substantial personal and financial risks to seek life-saving therapy in an industrialized country. Given the risks and legal prohibitions, they may conceal these reasons at the time of entry, or during interviews later.

Without better screening tools to identify those who will develop disease, and/or safer, shorter, and cheaper preventive therapy, efforts to screen and prevent TB among legal immigrants will remain expensive and provide little individual or public health benefit. Additional limitations are the problems of reexposure and reinfection during return trips, and the vast number of other types of migrants, including some who are seeking treatment that is unavailable in their own country. Expanding screening of more foreign born as they arrive in industrialized countries is merely applying more Band-Aids. The search for better diagnostic and therapeutic tools is essential as it could improve TB control in all countries. However, the most effective (not to mention more just) long-term solution is to increase our efforts to control TB in developing countries.

	References

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