TB Guidelines To Address Latent Disease

Key Point

About one quarter of TB cases occur among foreign-born persons who have been US residents for more than five years. Therefore, to eradicate TB in the US, it is necessary to screen that segment of the population for latent infection.

ATLANTA—For the United States to have any chance of reaching its goal of completely eliminating tuberculosis (TB), it has to address the problem of latent tuberculosis infection (LTBI) in foreign-born residents. Because of LTBI, the risk of full-blown TB remains high in these individuals years after immigration, a CDC study has shown.¹

“It was previously thought that TB risk for foreign-born persons reverted to that of the general US population within five years after their arrival,” explained principal investigator Kevin P. Cain, MD, in an interview with Pulmonary Reviews. “But we found that 24% of TB cases in this country occur in foreign-born persons who arrived more than five years ago,” he related. According to Dr. Cain, a medical epidemiologist in the CDC’s Division of Tuberculosis Elimination in Atlanta, former residents of sub-Saharan Africa and Asia are at particularly high risk.

It may be necessary to alter current TB guidelines, which recommend LTBI testing for foreign-born individuals who have been in the US for five years or less, Dr. Cain and colleagues concluded. In fact, the CDC, along with state TB controllers and the Advisory Council for the Elimination of TB, are currently working to update the guidelines using data from this study and many other data sources.

TB Rates Varied by Country, Region of Origin

Using 2004 data from the US National TB Surveillance database, Dr. Cain and colleagues determined TB rates among foreign-born citizens, stratified by duration of US residence and country and region of origin. Of the 14,517 TB cases reported, 7,806 occurred among foreign-born persons; there were 28 cases in people with an unknown country of origin.

The investigators excluded 975 foreign-born residents with TB, because their date of entry into the US was unknown. Among the remaining 6,831 foreign-born persons with TB, the duration of US residence was less than a year for 1,620 (24%), one to five years for 1,767 (26%), and longer than five years for 3,444 (50%).

“In 2004, the rate of TB disease among foreign-born persons was 21.5/100,000 person-years, whereas the rate among US-born persons was 2.7/100,000,” the investigators reported. The TB rates for foreign-born residents living in the US for a year or less, one to five years, and more than five years were 121/100,000, 30/100,000, and 11.9/100,000, respectively.

When the TB incidence of foreign-born persons living in the US for more than five years was analyzed, rates of more than 30/100,000 were found among those from the Philippines, Vietnam, South Korea, and Ethiopia. “These rates were higher than those in persons from Mexico and China who had been in the United States for one to five years,” the investigators observed.

When this analysis focused on the region of origin rather than the specific country, the TB rate was greater than 21/100,000 among foreign-born individuals from sub-Saharan Africa, South Asia, East Asia, and the Pacific. By contrast, the TB rate among persons from the Middle East and North Africa who had been living in the US for longer than five years was lower than 6/100,000.

Study Results Suggested Changes Are Needed

Dr. Cain’s findings refuted those from the mid to late 1990s showing relatively lower TB rates among foreign-born persons who had been in the US for more than five years. This earlier data provided a basis for the current recommendation to limit LTBI testing and treatment to those residing in the US for five years or less. However, this study suggests the need to amend the current TB guidelines to reflect the new findings, Dr. Cain asserted.

Other potentially useful measures to control TB in the foreign-born population include conducting studies to identify the best practices, assessing the feasibility of expanding immigrant screening for TB, and improving the screening techniques used overseas. Investment in international TB control programs and efforts to find and treat LTBI before those infected enter the US may be important as well.

“All of these approaches have great long-term potential to decrease the burden of TB in the foreign-born population,” Dr. Cain and colleagues stated. However, a comprehensive strategy will be needed, they added, “with different approaches for different groups.”

—Timothy Begany

Reference
1. Cain KP, Haley CA, Armstrong LR, et al. Tuberculosis among foreign-born persons in the United States: achieving tuberculosis elimination. Am J Respir Crit Care Med. 2007;175:75-79.

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