Description

Mycobacterium tuberculosis is a rod-shaped bacterium that can cause disseminated disease but is most frequently associated with chronic pneumonia. Transmission occurs when a contagious patient coughs, spreading the bacilli through the airborne route to a person sharing the same air space. The exposed person may acquire latent infection (sometimes abbreviated LTBI) or, depending on host factors, tuberculosis disease. Both conditions can usually be treated successfully with medications (1).

Multi-drug resistant or MDR-TB is TB resistant to at least two of the most effective drugs, isoniazid and rifampin (also called first-line drugs). XDR-TB is resistant to at least these two drugs and three of the six second-line drugs used to treat MDR-TB.

Occurrence

In many other countries, tuberculosis is much more common than in the United States, and it is an increasingly serious public health problem (2). Although MDR-TB occurs globally, it appears to be rare compared to drug-sensitive TB. XDR-TB is of particular concern among HIV-infected or other immunocompromised persons (see Maps 4-13, 4-14).

Risk for Travelers

To become infected, a person usually has to spend a relatively long time in a closed environment where the air was contaminated by a person with untreated tuberculosis who was coughing and who had numerous M. tuberculosis organisms (or tubercle bacilli) in secretions from the lungs or larynx. Infection is generally transmitted through the air; therefore, there is virtually no danger of its being spread by dishes, linens, and other items that are touched, or by most food products. However, it can be transmitted through unpasteurized milk or milk products (e.g., some cheeses) obtained from infected cattle (1). Documented sites of XDR-TB include crowded hospitals, prisons, homeless shelters, and other settings where susceptible persons come in contact with infected persons with TB disease.

Travelers who anticipate possible prolonged exposure to tuberculosis (e.g., those who could be expected to come in contact routinely with hospital, prison, or homeless shelter populations) should be advised to have a tuberculin skin test or QuantiFERON TB-Gold test (QFT-G) before leaving the United States (1,3). If the result is negative, they should have a repeat test approximately 8-10 weeks after returning (4,5). Because persons with HIV infection are more likely to have an impaired response to the test, travelers should be advised to inform their physicians about their HIV status. Except for travelers with impaired immunity, travelers who have already been infected are unlikely to be reinfected (1).

Travelers who anticipate repeated travel with possible prolonged exposure or an extended stay over a period of years in an endemic country should be advised to have a baseline two-step tuberculin test or a single-step QFT-G (4). If the baseline test is negative, annual screening would identify recent infection, which should prompt medical evaluation to exclude disease and treatment for latent infection.

CDC and state and local health departments have published the results of six investigations of possible tuberculosis transmission on commercial aircraft. In these six instances, a passenger or a member of a flight crew traveled on commercial airplanes while contagious with tuberculosis. In all six instances, the airlines were unaware that the passengers or crew members had tuberculosis. In two of the instances, CDC concluded that tuberculosis was probably transmitted to others on the airplane. The findings suggested that the risk of tuberculosis transmission from an infectious person to others on an airplane was greater on long flights (8 hours or more). The risk of exposure to tuberculosis was higher for passengers and flight crew members sitting or working near an infectious person because they were more likely to inhale droplets containing M. tuberculosis bacteria (6).

Based on these studies and findings, WHO issued recommendations to prevent the transmission of tuberculosis in aircraft and to guide potential investigations. The risk of tuberculosis transmission on an airplane does not appear to be greater than in any other enclosed space. To prevent the possibility of exposure to tuberculosis on airplanes, CDC and WHO recommend that persons known to have infectious tuberculosis travel by private transportation (that is, not by commercial airplanes or other commercial carriers), if travel is required. CDC and WHO have issued guidelines for notifying passengers who might have been exposed to tuberculosis aboard airplanes (6). Passengers concerned about possible exposure to tuberculosis should be advised to see their primary health-care provider for evaluation.

Prevention

Travelers should be advised to avoid exposure to known tuberculosis patients in crowded environments (e.g., hospitals, prisons, or homeless shelters) (5). Travelers who will be working in hospitals or health-care settings where tuberculosis patients are likely to be encountered should be advised to consult infection control or occupational health experts about procedures for obtaining personal respiratory protective devices (e.g., N-95 respirators), along with appropriate respirator selection and training (4). Additionally, tuberculosis patients should be educated and trained to cover coughs and sneezes with their hands or tissues to reduce spread. Otherwise, no specific preventive measures can be taken or are routinely recommended for travelers.

VACCINE

Based on WHO recommendations, the Bacille Calmette-Guérin (BCG) vaccine is used once at birth in most developing countries to reduce the severe consequences of tuberculosis in infants and children. However, BCG vaccine has variable efficacy in preventing the adult forms of tuberculosis and interferes with testing for latent infection. Therefore, it is not routinely recommended for use in the United States (7,8).

Treatment

Persons who are infected or who become infected with M. tuberculosis can be treated to prevent progression to tuberculosis disease (1,9). Updated American Thoracic Society/CDC recommendations for treatment of latent infection recommend 9 months of isoniazid as the preferred treatment and suggest that 4 months of rifampin is a reasonable alternative (1). Travelers who suspect that they have been exposed to tuberculosis should be advised to inform their physicians of the possible exposure and receive appropriate medical evaluation. CDC and the American Thoracic Society have published updated guidelines for targeted testing and treatment of latent infection (1,3). Recent data from the WHO suggest that resistance is relatively common in some parts of the world (10,11). Travelers who have test conversion associated with international travel should consult experts in infectious diseases or pulmonary medicine (1).

References

1. American Thoracic Society/Centers for Disease Control and Prevention. Targeted Tuberculin Testing and Treatment of Latent Tuberculosis Infection. Am J Respir & Critical Care Med. 2000;161:S221-47.
2. Global tuberculosis control - surveillance, planning, financing. WHO Report 2006. WHO/HTM/TB/2006.362 (http://publications/global_report/2006/pdf/full_report_correctedversion.pdf) PDF (3 MB/250 pages) Accessed 30 November 2006.
3. CDC. Guidelines for using the QuantiFERON-TB Gold test for detecting Mycobacterium tuberculosis infection, United States. MMWR Recomm Rep. 2005;54(RR-15);49-55.
4. CDC. Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care settings, 2005. MMWR Recomm Rep. 2005;54(RR-17).
5. CDC. Guidelines for the investigation of contacts of persons with infectious tuberculosis: Recommendations from the National Tuberculosis Controllers Association and CDC — MMWR Recomm Rep. 2005;54(RR-15):1-37.  
6. WHO. Tuberculosis and Air Travel: Guidelines for Prevention and Control (second edition). WHO 2006. WHO/HTM/TB/2006.363 (http://whqlibdoc.who.int/hq/2006/WHO_HTM_TB_2006.363_eng.pdf) PDF (602 KB/76 pages). Accessed 30 November 2006.  
7. CDC. The Role of BCG vaccine in the prevention and control of tuberculosis in the United States. (ACET and ACIP). MMWR Recomm Rep. 1996;45(RR-4).
8. CDC. Timing of tuberculosis screening and smallpox vaccination - recommendations for using smallpox vaccine in a pre-event vaccination program. MMWR Recomm Rep. 2003;52(RR-7).  
9. American Thoracic Society, CDC, and Infectious Disease Society of America. Treatment of tuberculosis. MMWR Recomm Rep. 2003;52(RR-11).
10. WHO. Anti-tuberculosis drug resistance in the world Report no. 3 WHO/HTM/TB/2004.343 (http://www.who.int/tb/publications/who_htm_tb_2004_343/en/index.html). Accessed 30 November 2006.
11. CDC. Emergence of Mycobacterium tuberculosis with extensive resistance to second-line drugs—worldwide, 2000-2004; MMWR Morbid Mortal Wkly Rep. 2006;55(11).

MAP 4-13 Tuberculosis incidence rate, 2004.

MAP 4-14 Multi-drug resistant tuberculosis, 2004.