Global migration has a substantial impact on the epidemiology of tuberculosis (TB) in the United States [1]. During 2001 through 2008, 54.6% (62,364) of the 114,323 new TB cases in the United States were diagnosed among foreign-born persons [2]. The rate of TB disease among foreign-born persons varies by duration of time in the United States [3], [4]. The highest rate is among foreign-born persons who have resided in the United States for 1 year or less (121.0 cases per 100,000 population), following by those residing in the United States for 1–5 years (30.0 cases per 100,000 population), and those residing in the United States for more than 5 years (11.9 cases per 100,000 population) [4].

Based on their visa status at the time of arrival, foreign-born persons may be classified as ‘immigrants and refugees’ who intend to reside permanently in the United States, and ‘nonimmigrant visitors’ who stay in the United States temporarily (e.g., students, exchange visitors, temporary workers, tourists, and business travelers) [5]. Approximately 500,000 immigrants and refugees, 163 million nonimmigrant visitors, and an unknown number of unauthorized visitors are admitted to the United States annually [5]–[7]. Among these newly arrivals, only immigrants and refugees are required to undergo screening for TB prior to their arrival in the United States [8]. Overseas TB screening in immigrants and refugees is a relatively high-yield intervention [9]–[11]. During the following-up evaluations after arrival in the United States, active TB is diagnosed in 7.0% of immigrants and refugees with an overseas diagnosis of smear negative TB (e.g., a chest radiograph was suggestive of active TB but sputum smears were negative for acid-fast bacilli on 3 consecutive days), and in 1.6% of those with an overseas diagnosis of inactive TB (e.g., a chest radiograph was suggestive of TB that was no longer clinically active) [9]. Many nonimmigrant visitors are from countries with a high incidence of TB and can stay in the United States for a relatively long period of time [5], [8]. Due to unavailable data for immigration status of foreign-born TB cases in the U.S. National TB Surveillance System [2], it is unclear what extent of the unscreened nonimmigrant visitors contributes to the burden of foreign-born TB in the United States. We utilized data from the U.S. Department of Homeland Security (DHS), the U.S. Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO), to estimate the incidence of TB among foreign-born persons who had resided for 1 year or less after arrival in the United States during 2001 through 2008.

Of 1,479,542,654 admissions of foreign-born persons to the United States from 2001 through 2008, 0.2% (3,625,619) were immigrants and refugees, 1.5% (22,328,345) were students/exchange visitors and temporary workers, 15.6% (230,673,431) were tourists and business travelers, 0.1% (2,215,260) were diplomats and other representatives, and 82.5% (1,220,700,000) were Canadian and Mexican nonimmigrant visitors without an I-94 form (Table 1). We estimated that 11,500 TB incident cases, including 291 MDR-TB incident cases, occurred among 20,989,738 person-years for the 1,479,542,654 newly arrived foreign-born persons (Table 1). During the same period, the U.S. National TB Surveillance System has reported that 12,099 TB cases, including 249 MDR-TB cases, were diagnosed among foreign-born persons within 1 year after their arrival in the United States.

Of the 11,500 estimated TB incident cases, 41.6% (4,783) occurred among immigrants and refugees, 36.6% (4,211) among students/exchange visitors and temporary workers, 13.8% (1,589) among tourists and business travelers, 0.7% (84) among diplomats and other representatives, and 7.3% (834) among Canadian and Mexican nonimmigrant visitors without an I-94 form (Table 1). Overall, 1.3% of the 1,479,542,654 admissions of foreign-born persons were from high-incidence countries, but they accounted for 60.9% of the 11,500 estimated TB incident cases among the newly arrived foreign-born persons. Only 44.8% of the 3,625,619 admissions of immigrants and refugees were from high-incidence countries, but they accounted for 80.0% of the 4,783 estimated TB incident cases among the newly arrived immigrants and refugees (Table 2); 18.7% of the 22,328,345 admissions of students/exchange visitors and temporary workers were from high-incidence countries, but they accounted for 60.4% of the 4,211 estimated TB incident cases among the newly arrived students/exchange visitors and temporary workers (Table 3); 5.4% of the 230,673,431 admissions of tourist and business travelers were from high-incidence countries, but they accounted for 36.4% of the 1,589 estimated TB incident cases among the newly arrived tourists and business travelers (Table 4).

Only 29.8% of immigrants and refugees were from the top 5 countries (the Philippines, India, Vietnam, China, and Haiti), but they accounted for 44.8% of the estimated TB incident cases among the newly arrived immigrants and refugees (Table 2); 23.1% of students/exchanges visitors and temporary workers were from the top 5 countries (India, China, South Africa, South Korea, and the Philippines), but they accounted for 56.6% of the estimated TB incident cases among the newly arrived students/exchange visitors and temporary workers (Table 3); 35.3% of tourists and business travelers were from the top 5 countries (Mexico, Japan, South Africa, China, and India), but they accounted for 42.4% of the estimated TB incident cases among the newly arrived tourists and business travelers (Tables 4).

The top 5 newly arrived foreign-born populations with the largest number of estimated TB incident cases per 100,000 admissions were immigrants and refugees from high-incidence countries (235.8 cases per 100,000 admissions, 95% confidence interval [CI], 228.3 to 243.3), students/exchange visitors and temporary workers from high-incidence countries, 60.9 cases per 100,000 admissions (95% CI, 58.5 to 63.3), immigrants and refugees from medium-incidence countries (55.2 cases per 100,000 admissions, 95% CI, 51.6 to 58.8), students/exchange visitors and temporary workers from medium-incidence countries (14.3 cases per 100,000 admissions, 95% CI, 13.6 to 15.0), and diplomats and other representatives from high-incidence countries (13.2 cases per 100,000 admissions, 95% CI, 9.8 to 16.7; Tables 2, 3, 4 & Figure 1).

We estimated that newly arrived nonimmigrant visitors contribute substantially to the burden of foreign-born TB in the United States. From 2001 through 2008, on average, 1,438 TB incident cases per year were estimated to occur among newly arrived foreign-born persons in the United States. Of the 1,438 annual estimated TB incident cases, 41.6% (598) were among immigrants and refugees who were screened for TB overseas, and 58.4% (840) were among nonimmigrant visitors who were not screened for TB overseas. To reduce the incidence of TB in newly arrived foreign-born populations in the United States, strategies to target nonimmigrant visitors should be considered. Such strategies may include screening for TB in nonimmigrant visitors if they are from high-incidence countries and also intend to stay in the United States for a long period of time.

Overseas TB screening is a relatively high-yield intervention [9]–[11], but it is only required for U.S.-bound immigrants and refugees [8]. This intervention consists of two integrated components, screening for TB overseas and follow-up evaluations after arrival in the United States [9], [10]. One objective of overseas TB screening is to prevent the importation of TB into the United States, and the other objective is to identify immigrants and refugees with suspected TB for follow-up evaluations in the United States [9]. A recent study has reported that during follow-up evaluations in the United States, active pulmonary TB is diagnosed in 7.0% of immigrants and refugees with an overseas diagnosis of smear-negative TB and 1.6% of those with an overseas diagnosis of inactive TB [9]. Due to the large volume of annual admissions and the overall low TB rate, screening for TB in nonimmigrant visitors to the United States is considered to be infeasible and of low-yield [22], [23]. However, this intervention could be effective if it targets those who are from countries with a high incidence of TB, particularly those who also intend to stay in the United States for a long time period. Since overseas TB screening in approximately 400,000 immigrants and refugees per year has been feasible and effective [8]–[10], we considered the potential impact of screening for TB in selected nonimmigrant visitors. For example, during 2001 through 2008, there were approximately 522,000 annual admissions of students/exchange visitors and temporary workers per year were from high-incidence countries, and they accounted for 22.1% of the 1,438 annual estimated TB incident cases in the newly arrived foreign-born persons. In comparison, there were approximately 203,000 annual admissions of immigrants and refugees from high-incidence countries and 210,000 annual admissions from medium-incidence countries, and they accounted for 33.2% and 8.1% of the 1,438 annual estimated TB incident cases in the newly arrived foreign-born persons, respectively. Furthermore, newly arrived students/exchange visitors and temporary workers from high-incidence countries had a larger number of estimated TB incident cases per 100,000 admissions than any other newly arrived foreign-born populations except immigrants and refugees from high-incidence countries. Post-arrival follow-up evaluations of students/exchange visitors and temporary workers with suspected TB is likely possible since they stay in the United States for an average of 180 days [13].

From 2001 through 2008, on average, 28.8 million of tourists and business travelers per year were admitted to the United States, but they accounted for 13.8% of the 1,438 annual estimated TB incident cases in the newly arrived foreign-born persons. Due to the large annual admissions and a small number of estimated TB incident cases per 100,000 admissions, intervention of TB in tourists and business travelers is likely to be infeasible and of low-yield. Newly arrived diplomats and other representatives likely had a small impact on foreign-born TB in the United States. Despite the large volume of admissions, Canadian and Mexican nonimmigrant visitors without an I-94 form only accounted for 7.3% of the estimated TB incident cases among the newly arrived foreign-born persons.

There are several barriers to implement the potential intervention for nonimmigrant visitors to the United States. Firstly, it increases the cost and workload for federal governmental agencies, as well as state and local health departments. Secondly, requiring proof of TB screening of nonimmigrant visitors would significantly deviate from the U.S. open-door policy and would have great logistical and political implications [22]. Finally, many high-incidence countries may not have the facility and capacity to implement the TB screening program for U.S.-bound nonimmigrant visitors.

Canada and some European countries require TB screening for long-term nonimmigrant visitors from medium and high-incidence countries [24], [25]. In the United States, some nonimmigrant visitors have TB screening after arrival [26]–[29]. Approximately 600,000 nonimmigrant visitors who have been living in the United States for at least 1 year apply to adjust their status to U.S. permanent residence annually and are required to undergo TB screening [5], [8], [26]–[28]. Some U.S. universities and colleges require international students to have TB screening [29]. Despite these efforts, the TB rate among newly arrived foreign-born persons remains very high in the United States [3], [4], indicating additional TB interventions are needed.

We did not predict the potential yield of screening latent TB infection (LTBI). The current algorithm for overseas TB screening in U.S.-bound immigrants and refugees focuses on preventing the importation of active TB [30], [31]. However, this analysis estimated that there were 1,438 TB incident cases occurred among newly arrived foreign-born persons annually, indicating that screening and treating LTBI is important. A current study has also recommended that U.S. TB control programs should focus on finding and treating LTBI prior to or shortly arrival in the United States since 83.7% of the U.S. foreign-born TB cases are attributed to reactivation TB [32].

From 2001 through 2008, we estimated that 11,500 TB incident cases, including 291 MDR-TB incident cases, occurred among foreign-born persons within 1 year after arrival in the United States. During the same period, according to the U.S. National TB Surveillance System, 12,099 TB cases, including 249 MDR-TB cases, were diagnosed among foreign-born persons within 1 year after arrival in the United States [2]. However, we should be cautioned for comparing our estimate with the reported cases in U.S. National TB Surveillance System since 1) immigration status of foreign-born TB cases was unavailable in the U.S. National TB Surveillance System, 2) our estimate included cases among foreign-born persons with a short length of stay, but these cases might not seek care in the United States and were less likely to be reported to the system, 3) our estimate included incident cases only, but both incident and prevalent cases were reported to the system, and 4) our estimate did not include incident cases among newly arrived unauthorized visitors, but cases among unauthorized visitors were reported to the system.

We compared our estimates with the results of some previous studies. One study reported that, of 114 foreign-born TB cases diagnosed in Tarrant County, Texas, 59.0% was among immigrants, 28.0% among unauthorized visitors, and 19.0% among nonimmigrant visitors. However, this study included foreign-born persons who had been in the United States for >1 year and also likely included more unauthorized visitors because of the study location [33]. Another study found that, in California, 38.1% of 2,549 foreign-born TB cases within 1 year after arrival in the United States were among immigrants and refugees with an overseas TB diagnosis [34]. A recent study reported that, 4,285 immigrants and refugees with an overseas diagnosis of smear-negative TB and 4,480 immigrants and refugees with an overseas diagnosis of inactive TB were admitted to the United States annually during 1999 through 2005 [9]. Based on the findings in the same study, 372 cases of active pulmonary TB (4,285*7.0%+4,480*1.6%) were likely diagnosed among immigrants and refugees with an overseas TB diagnosis annually. In comparison, we found that immigrants and refugees accounted for 41.6% (598) of the 1,438 annual estimated TB incident cases in newly arrived foreign-born persons. Our estimates were larger since we included TB incident cases in newly arrived immigrants and refugees without an overseas TB diagnosis.

This analysis had several limitations. Firstly, the DHS-estimated length of stay might be biased since DHS used the 2003 departure data for nonimmigrant visitors with an I-94 form and the 2004 departure data for Canadian and Mexican nonimmigrant visitors without an I-94 form in its estimations. Secondly, we did not estimate the incidence of TB among newly arrived unauthorized visitors due to the lack of available data. DHS has reported that, of the estimated 10.8 million unauthorized visitors in January 2009, 4.4% (470,000) were from two high-incidence countries (the Philippines and India) and 79.6% (8.6 million) were from eight medium-incidence countries (Mexico, El Salvador, Guatemala, Honduras, South Korea, Ecuador, Brazil, and China) [7]. DHS has also estimated that 37.0% (4.0 million) of the 10.8 million unauthorized visitors in January 2009 had entered the United States in January 2000 or later [7], but it did not estimate the annual arrivals of unauthorized visitors by country of citizenship. Finally, U.S.-bound immigrants and nonimmigrant visitors likely have better socioeconomic status, therefore might have a lower TB incidence rate than the general population of their country of citizenship. However, a recent study has found that, for foreign-born persons from 9 of the top 10 countries of origin with the largest number of TB cases in the United States, the TB rates among those who have been in the United States for 1 year or less after arrival are actually higher than the TB rates of their countries of origin [4].

Newly arrived immigrants and refugees, as well as nonimmigrant visitors, contribute substantially to the burden of foreign-born TB in the United States. CDC has already implemented modernized TB screening which includes mycobacterial cultures, drug-susceptibility testing, and directly observed therapy for immigrant visa applicants in the Philippines, China, Vietnam, Indian, Mexico, and other countries [31], [35]. To further reduce the incidence of TB in foreign-born populations in the United States, strategies to target nonimmigrant visitors, especially those who are from high-incidence countries and also intend to stay for a long period of time in the United States, should be considered. Cost-effectiveness analyses and studies to better estimate the TB rates in U.S.-bound foreign-born populations could guide decisions about which populations should be targeted.