Testing for Latent Tuberculosis. Applying the Best of Intentions

For latent tuberculosis infection testing, the contemporary public health mantra is “intent to test is intent to treat” (1). From both public health and economic perspectives, this strategy seems quite practical—that is, focus limited resources on the highest-risk individuals to obtain the most “bang” for the precious public health “buck.” Reactivation of latent tuberculosis accounts for the large majority of active tuberculosis cases in the United States, so that latent infection screening and treatment remains the cornerstone of the U.S. tuberculosis elimination strategy (1–3). Based on the impressive decline in U.S. tuberculosis incidence over the last 20 years, the latent infection “intent to test is intent to treat” approach appears to be a valuable component of an overall successful program (4). So, who should we intend to test (i.e., target) for latent tuberculosis infection? The last Centers for Disease Control and Prevention guidelines for targeted latent tuberculosis infection testing (published 14 years ago) identified high-risk groups based on contemporary risk stratification for progression from latent infection to active disease (1). However, important new risks emerged between that 2000 statement and the present day. Principal among them was the advent of immune-suppressive “biologic” agents for treatment of chronic noninfectious inflammatory processes that could produce profound vulnerability for progression from latent infection to active disease. Although they were quickly and widely recognized for their infectionpromoting potential, the last latent tuberculosis guidelines predated their emergence (1). As Baker and colleagues point out in this issue of AnnalsATS (pp. 480–488), other important areas impacting latent tuberculosis infection testing are also changing, in this case not based on some new insidious threat to immune function, but rather as a consequence of demographic shifts that are a function of multiple social and economic factors altering immigration patterns between Mexico and the United States (5). The previous guidelines suggested that foreign-born individuals living in the United States for less than 5 years should be tested for latent infection and treated if diagnosed (1). This recommendation was apparently based on the dual observations that the majority of new tuberculosis cases in foreign-born individuals were due to reactivation of latent disease and that 50% of the foreign-born individuals with active disease were diagnosed within 5 years after entering the country (1, 2). Two epidemiologic trends, one foreseeable and one serendipitous, intervened to require reconsideration of this recommendation. First, and predictably, the number of foreign-born individuals diagnosed with tuberculosis has become a progressively larger percentage of total U.S. tuberculosis morbidity. As U.S tuberculosis control measures became increasingly successful, and the tuberculosis incidence rate in U.S.-born individuals has declined to approximately 1/100,000 population, the primary source of new active disease diagnosed in the United States is not surprisingly individuals from areas of the world where tuberculosis control is not as successful (4). Tuberculosis in foreign-born individuals now accounts for more than 60% of U.S. tuberculosis morbidity. Second, and less predictable (except perhaps to demographics cognoscenti), were social, economic, and political factors that slowed the pace of immigration from Mexico into the United States, making longer-term immigrant residents a larger percentage of the total pool of foreign-born persons from Mexico in the United States. The public health consequences of these socioeconomic forces has been to make long-term U.S. immigrant residents from Mexico a more important target for tuberculosis control efforts, specifically latent infection diagnosis and treatment (2, 5). In the study by Baker and coworkers, among persons from Mexico living in the United States formore than 5 years, there was an increase in tuberculosis cases and an increase in population as opposed to newly arrived persons, who had a decrease in tuberculosis cases and a decrease in patient population. In 2010, 66.7% of Mexico-born cases were among non–recently arrived persons (compared with 51% in 2000). “If current trends continue, TB morbidity among Mexico-born persons in the United States will be increasingly driven by the non–recently arrived population” (5). The suggestion that foreign-born persons living in the United States for more than 5 years should also receive the same scrutiny as those here less than 5 years is not new (6). From the advent of the 2000 guidelines, it was noted that 50% of the new tuberculosis cases occurred in immigrants who resided in the United States for more than 5 years. In a recent study using a model