Tuberculosis Among Foreign-born Persons in the United States

Abstract & Commentary

By Lin H. Chen, MD

Dr. Chen is Assistant Clinical Professor, Harvard Medical School, Director, Travel Medicine Center, Mt. Auburn Hospital, Cambridge, MA.

Dr. Chen reports no financial relationships related to this field of study.

Synopsis: In the United States, tuberculosis (TB) case rates and drug resistance are much higher in foreign-born persons. The greatest risk of active TB is associated with individuals from sub-Saharan Africa and southeast Asia, and those of older age at arrival. Although risk is higher in persons who arrived recently in the U.S., the majority of TB cases have occurred in foreign-born persons who have lived in the U.S. for more than 2 years.

Source: Cain KP, et al. Tuberculosis among foreign-born persons in the United States. JAMA 2008;300(4):405-412.

The authors analyzed the cases of tuberculosis that occurred in the United States among foreign-born persons from 2001 through 2006. During this period, 46,970 cases of TB were reported among foreign-born persons, of whom 28% were recent entrants who were within 2 years of entry to the United States, and 69% were not recent entrants. TB case rates were highest in recent entrants. When analyzed by country of birth, case rates in recent entrants were 3-7 times higher than among non-recent entrants. Recent entrants born in sub-Saharan Africa and Southeast Asia had annual case rates > 250/100,000 persons. Cases in persons born in sub-Saharan Africa and southeast Asia account for 53% of all TB cases in foreign-born individuals, although people born in these regions account for only 22% of the foreign-born population in the United States. Recent entrants from Central America, Eastern Europe, the Pacific Islands, and South, East, and Central Asia had annual case rates of > 100/100,000 persons.

Moreover, TB rates among foreign-born persons remained at > 10/100,000 persons even among those who have lived in the United States for more than 2 decades, 4 times higher than among U.S.-born persons. When analyzed by age at arrival to the United States, TB rates rose with increased age at arrival. In recent entrants, annual case rates increased from 25-30/100,000 persons in those who arrived at age < 5 years, to > 100/100,000 persons in those who arrived at age > 50 years. Similarly, in non-recent entrants, the annual case rates were increased from 5/100,000 persons in those who arrived at age < 5 years, to > 60/100,000 persons in those who arrived at age > 60 years.

Drug resistance is another problem in foreign-born persons with tuberculosis, occurring in 10-11% of bacterial isolates compared to 4% in U.S.-born persons. INH-resistance was highest in recent entrants from Vietnam (20%), Peru (18%), the Philippines (17%), and China (16%). Multidrug-resistant TB occurred in 6% of recent entrants from Peru and China, compared to 0.6% among U.S.-born persons.

The authors assessed pre-arrival screening, which currently includes chest radiography in persons aged 15 year or older, plus sputum smear if found to have abnormal radiograph. They found that 4499 foreign-born persons were reported with TB within 3 months of arrival to the United States, with 91% having pulmonary disease. Abnormal chest radiographs and positive sputum smears were found in 1211, which could have been identified by current overseas screening. Another 1502 had an abnormal chest radiograph, negative sputum, but positive sputum culture. Screening with CXR, sputum smear and culture would identify the latter group of individuals, 46% of whom are from Vietnam or the Philippines.

Commentary

Mycobacterium tuberculosis infects about 30% of the world's population.1 In 2006, there were 9.2 million new TB infections and 1.7 million deaths attributed to TB.2 In the United States, the majority of TB cases occur in foreign-born persons and racial/ethnic minorities.3 In 2007, foreign-born persons in the United States had a TB rate that was 9.7 times higher than in U.S.-born persons.3 The CDC found TB rates to be much higher among Hispanics, blacks, and Asians (7.4, 8.3, and 22.9 times higher, respectively) than in non-Hispanic whites; foreign-born persons comprised the vast majority of TB cases among Hispanics (77.2%) and among Asians (96.1%).3

From October 1998 to October 1999, the CDC assessed the ability of overseas screening with chest radiographs, plus 3 AFB sputum smears for those with abnormal chest radiographs, to detect pulmonary TB among U.S.-bound immigrants. At that time, overseas screening in Vietnam found that among 1179 adult immigration applicants with abnormal chest radiographs, 82 (7.0%) had positive acid-fast bacilli smears, and 183 (15.5%) had positive Mycobacterium tuberculosis cultures.4 The sensitivity of chest radiographs plus AFB smears was only 34% and inadequate to control tuberculosis among foreign-born persons.4

In 2007, the CDC initiated additional TB screening for U.S.-bound immigrant applicants, which included: targeted tuberculin skin testing of children 2-14 years old who live in countries with high TB incidence (i.e., WHO-estimated rates of > 20 cases per 100,000 population) and all known TB contacts; and adding cultures and drug-susceptibility testing for persons with suspected TB.3 These new initiatives were started in 2007 in Mexico, Nepal, the Philippines, and Thailand, and are being expanded in 2008 to Vietnam and some African countries.3

The report by Cain, et al., substantiates data from past TB analyses, and highlights the following:

  • Foreign-born individuals who arrived in the United States within 2 years are 3-7 times more likely to have active TB infection than non-recent entrants.
  • Persons born in sub-Saharan Africa and Southeast Asia have the highest risk of having been infected with TB.
  • Older age at arrival to the United States is associated with increased case rates.
  • TB drug resistance is more common in foreign-born persons compared to U.S.-born persons.
  • Pre-arrival TB culture in addition to chest radiograph and sputum smear should be useful for screening persons born in Vietnam or the Philippines.
  • Non-recent entrants comprised the majority (69%) of the TB cases in foreign-born persons, clearly an important group to target for diagnosis and treatment.

The great proportion of TB among foreign-born persons underscores the importance to screen persons born in high-incidence countries for TB. Screening for latent TB is even more important in foreign-born persons who came to the United States before the enhanced overseas screening was instituted. A model of lifetime TB reactivation estimated the risk to be at least 20% among most persons with ≥ 10 mm of PPD induration who have either evidence of old healed TB or are HIV infected.5 The lifetime risk is estimated to be 10-20% among persons with recent tuberculin skin test conversion, among persons younger than 35 years of age who are on infliximab treatment and have ≥ 15 mm of induration, and in children ≤ 5 years of age with ≥ 10 mm induration.5

The development of whole-blood interferon-g release assays holds promise as alternative TB screening tools. These tests avoid the cross reactivity due to immunization with BCG, which has plagued the interpretation of tuberculin skin tests in the past. The tests have recently been approved by the FDA, and wider use is anticipated in the near future.6,7

Travel medicine practitioners can contribute to the TB control efforts through the screening of travelers who were born in high-risk countries for TB (sub-Saharan Africa and Southeast Asia in particular, but also Central America, Eastern Europe, the Pacific Islands, and South, East, and Central Asia). Travelers who are visiting friends and relatives are especially at risk, even if prior TB screenings were negative, when they plan to spend time in countries with high risk for TB. The TB screening can be done when travelers present for pre-travel evaluations, or can be performed after the travelers return. If available, screening can utilize a interferon-g release assay when there is concern about BCG-associated positivity contributing to the positive tuberculin skin test.

References

  1. Corbett EL et al. The growing burden of tuberculosis. Arch Intern Med 2003;163:1009-1021.
  2. WHO. Global tuberculosis control: Surveillance, planning, finance: WHO report 2008. Geneva, World Health Organization. Available at http://www.who.int/tb. Accessed May 7, 2008.
  3. CDC. Trends in tuberculosis—United States, 2007. MMWR 2008;57(11):281-285.
  4. Maloney SA, et al. Assessing the performance of overseas tuberculosis screening programs: A study among US-bound immigrants in Vietnam. Arch Intern Med 2006 Jan 23;166(2):234-40.
  5. Horsburgh CR. Priorities for the treatment of latent tuberculosis infection in the United States. N Engl J Med 2004;350(20):2060-2067.
  6. Mazurek GH, Weis SE. Prospective comparison of the tuberculin skin test and 2 whole-blood interferon-g release assays in persons with suspected tuberculosis. Clin Infect Dis 2007;45:837-845.
  7. Mazurek GH, et al. Detection of Mycobacterium tuberculosis infection in United States navy recruits using the tuberculin skin test or whole-blood interferon-g release assays. Clin Infect Dis 2007;45:826-836.