Travel: TB or not TB?
September 1, 2000 6 minutes read
Travel: TB or not TB?
abstract & commentary
Synopsis: The risk of tuberculosis in long-term travelers to developing countries is significant.
Source: Cobelens FGJ, et al. Risk of infection with Mycobacterium tuberculosis in travellers to areas of high tuberculosis endemicity. Lancet 2000;356:461-465.
Cobelens and colleagues examined the risk of infection with Mycobacterium tuberculosis in adults traveling for 3-12 months to countries with an annual incidence of tuberculosis (TB) of 1% or more. Significant underlying illness, prior evidence of tuberculous infection, and prior bacille Calmette-Guèrin (BCG) vaccination were among the exclusion criteria.
Twelve infections were detected among 656 subjects who were skin tested both prior to travel, which lasted a median duration of 23 weeks, and after return. Only two of the 12 had evidence of clinically active pulmonary TB. The incidence of tuberculous infection was 3.5 per 1000 person-months of travel, while the incidence of active TB was 0.6 per 1000 person-months. The incidence was highest in health care workers; among those with direct patient contact it was 9.8 per 1000 person-months. Non-health care workers had an incidence of 2.8 per 1000; this was calculated by Cobelens et al to be approximately equivalent to an annual incidence of 3.3%.
Comment by Stan Deresinski, MD, FACP
Travel allows exposure to other cultures. It may also allow exposure to other diseases. I still recall with dread a taxi ride in Bangkok —being interminably stuck in traffic with a driver who could not stop coughing. Fortunately, I did not convert my PPD as a result.
In the United States, the annual incidence of TB in 1998 was 6.8 per 100,000 population. In contrast, the World Health Organization’s (WHO) estimates of TB case rates per 100,000 population in 1995 were: 241 in southeast Asia, 140 in the western Pacific, 242 in Africa, 168 in the eastern Mediterranean, 123 in the Americas (except the United States and Canada), 47 in Eastern Europe, and 23 in Western industrialized countries and Japan.
The data presented by Cobelens et al suggest the risk of acquiring TB in these long-term travelers was significantly greater than the reported risks of travelers to developing countries of acquiring cholera, malaria, or meningococcal disease, but comparable to that of acquiring hepatitis A virus infection.1-5 The latter is estimated to be three per 1000 travelers per month among unprotected travelers, including those who stay in luxury hotels, but is almost seven times greater among those who eat and drink under poor hygienic conditions.5
Children who travel may be at even greater risk than the adults studied here. U.S.-born children who have traveled to countries with a high prevalence of TB in the previous 12 months were 4.7 times (95% CI, 2.0-11.2) more likely to have a postive tuberculin reaction than those who had not traveled.6 In addition, children who had a household visitor from a country having a high prevalence of TB were 2.4 times more likely to have a positive skin test than were those who did not have a visitor (95% CI, 1.0-5.5).
Another important issue to the estimated 2 billion (or more) passengers who will fly annually by 2005 is the potential for transmission of TB during air travel.7 The CDC has reported seven investigations involving one flight attendant and six passengers with infectious TB, more than 2600 potentially exposed passengers and crew, and a total of 191 different flights.8,9 There was, however, evidence of transmission in only two episodes. In one, evidence of transmission from the flight attendant to other crew members was found for those with 12 or more hours of exposure while working with the flight attendant with TB. Evidence of transmission from passenger to passenger was only found for a few passengers who were seated in close proximity to the passenger with active TB and only on one flight of more than eight hours duration. No secondary cases of active TB were identified in any of the investigations.
The Canadian Public Health Service has made the following recommendations for prevention of TB in travelers:10
1. All travelers to high-prevalence countries, particularly those traveling or living overseas with children, should be informed of the risk of TB.
2. Travelers with significant immune compromise, such as HIV, should be informed of the serious risk associated with TB exposure and of the important limitations of either a BCG vaccination or periodic skin testing with chemoprophylaxis in the event of conversion.
3. Travelers should be advised to avoid consumption of unpasteurized milk since it may contain M. bovis or other pathogenic organisms.
4. Medical assessment of domestic workers or other host-country nationals who are in close contact with the traveler or the traveler’s family, particularly if a chronic cough is present, may reduce the risk of TB exposure as well as potentially benefiting the local person involved.
5. Those working in health care settings in developing countries should follow current infection control recommendations to the greatest degree possible to minimize the risk of exposure to TB.
6. Travelers going to high-prevalence countries for extended periods (e.g., 3 months or less, if risk is expected to be high) or working in a health care setting in a developing country for any period of time should be offered a TST with five tuberculin units of purified protein derivative (including two-step testing where indicated) unless there is a past history of tuberculosis or a well-documented previous positive TST.
7. If the initial TST is found to be positive, current management guidelines should be followed.
8. If the TST is negative, the individual should be informed about practical means of avoiding TB exposure. Persons should be advised to choose either BCG vaccination or a TST at least every two years, but preferably annually, as well as 3-6 months after leaving the high-prevalence area. If a TST becomes positive, the traveler should be assessed by someone with expertise in TB to consider the use of chemoprophylaxis and to determine the chemoprophylactic regimen.
9. In making the choice between BCG vaccination or periodic skin testing with prophylaxis in the event of conversion, the following factors should be considered:
• anticipated feasibility of, and compliance with, repeated skin testing and chemoprophylaxis;
• likelihood of isoniazid intolerance (age, liver disease, excess alcohol use);
• likelihood that an infecting strain of M. tuberculosis may be isoniazid-resistant (depends on local rates of primary resistance);
• individual preference;
• age—the role of BCG vaccination may be particularly important in children, especially those younger than 1 year of age.
10. Where possible, BCG should be administered at least four weeks before the anticipated exposure to TB.
11. A "baseline" measurement of the tuberculin reaction three months after BCG vaccination may be considered to aid in the interpretation of any subsequent TSTs.
12. Regardless of the duration of travel or the preventive measures used, TB must be considered in the differential diagnosis of illness in travelers returning from high-prevalence countries as well as in immigrants from those countries.
The emphasis on BCG in these Canadian recommendations is greater than would be seen with U.S. recommendations. However, it seems reasonable that infants who will be staying in a country with a high prevalence of TB are candidates for BCG vaccination.11-13 Vaccination may also be considered in health care workers, although the potential value of this approach is less certain.14,15
References
1. Morger H, et al. BMJ 1983;286:184-186.
2. Lobel HO, et al. Bull World Health Organ 1990;68: 209-215.
3. Behrens RH, Roberts JA. BMJ 1994;309:918-922.
4. Koch S, Steffen R. J Travel Med 1994;1:4-7.
5. Steffen R, et al. JAMA 1994;272:885-889.
6. Lobato MN, Hopewell PC. Am J Respir Crit Care Med 1998;158:1871-1875.
7. Driver CR, et al. JAMA 1994;272:1031-1035.
8. CDC. TB Notes Newsletter 1999;1.
9. http://www.who.int/gtb/publications/index.
10. Committee to Advise on Tropical Medicine and Travel (CATMAT). Canada Communicable Disease Report—1997;23:(ACS-5).
11. Colditz GA, et al. JAMA 1994;271:698-702.
12. Colditz GA, et al. Pediatrics 1995;96:29-35.
13. Rodriques LC, et al. Int J Epidemiol 1993;22: 1154-1158.
14. Brewer TF, Colditz GA. Clin Infect Dis 1995;20: 136-142.
15. CDC. MMWR Morb Mortal Wkly Rep 1996;45: (RR-4):1-18.
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