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Tuberculosis

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Posted by  Simba Saturday, 06 May 2006 20:38

Tuberculosis

Tuberculosis

Description

Mycobacterium tuberculosis is a rod-shaped bacterium that can cause disseminated disease but is most frequently associated with pulmonary infections. The bacilli are transmitted by the airborne route and, depending on host factors, may lead to latent tuberculosis infection (sometimes abbreviated LTBI) or tuberculosis disease (TB). Both conditions can usually be treated successfully with medications.

Occurrence

In many other countries, tuberculosis is much more common than in the United States, and it is an increasingly serious public health problem.

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 voice box (larynx). Infection is generally transmitted through the air; therefore, there is virtually no danger of its being spread by dishes, linens, and items that are touched, or by most food products. However, it can be transmitted through unpasteurized milk or milk products obtained from infected cattle.

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 before leaving the United States. If the reaction is negative, they should have a repeat test approximately 12 weeks after returning. Because persons with HIV infection are more likely to have an impaired response to the tuberculin skin test, travelers who are HIV positive should be advised to inform their physicians about their HIV infection status. Except for travelers with impaired immunity, travelers who already have a positive tuberculin reaction are unlikely to be reinfected.

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 two-step baseline testing and, if the reaction is negative, annual screening, including a tuberculin skin test.

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 infectious with tuberculosis. In all six instances, the airlines were unaware that the passengers or crew members were infected with 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 might inhale droplets containing M. tuberculosis bacteria.

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. Passengers concerned about possible exposure to tuberculosis should be advised to see their primary health-care provider for a tuberculosis skin test.

Prevention

Vaccine

Based on WHO recommendations, the Bacille Calmette-Guérin (BCG) vaccine is used 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 tuberculosis infection. Therefore, it not routinely recommended for use in the United States.

Other

Travelers should be advised to avoid exposure to known tuberculosis patients in crowded environments (e.g., hospitals, prisons, or homeless shelters). 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 fitting and training. 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.

Treatment

Persons who are infected or who become infected with M. tuberculosis can be treated to prevent progression to tuberculosis disease. Updated American Thoracic Society (ATS)/CDC recommendations for treatment of latent tuberculosis infection recommend 9 months of isoniazid as the preferred treatment and suggest that 4 months of rifampin is a reasonable alternative. 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 ATS have published updated guidelines for targeted tuberculin skin testing and treatment of latent tuberculosis infection. Recent data from the WHO suggest that resistance is relatively common in some parts of the world. Travelers who have tuberculin skin test conversion associated with international travel should consult experts in infectious diseases or pulmonary medicine.

Bibliography

  • 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.
  • American Thoracic Society/Centers for Disease Control and Prevention. Update: Adverse Event Data and Revised American Thoracic Society/CDC Recommendations Against the Use of Rifampin and Pyrazinamide for Treatment of Latent Tuberculosis Infection—United States, 2003. MMWR Morbid Mortal Wkly Rep . 2003;52:735-9.

- Michael Iademarco

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