CDC: Urge foreign-born employees to test for TB
HCWs with latent TB pose huge risk to patients
If your organization includes foreign-born employees, CDC figures on tuberculosis (TB) are important for their health and the health of others, particularly in health care facilities.
CDC figures from 2005 indicate that the rate of TB in the United States was the lowest recorded since national reporting began in 1953, with a total of just more than 14,000 cases reported. That's the good news; the bad is that the rate of decline has slowed dramatically in recent years, and the rate of TB among foreign-born residents is nearly nine times greater than for people born in the United States.
According to Vanderbilt University medical professors Timothy R. Sterling, MD, and David W. Haas, MD, health care workers born outside the United States may assume they are protected by immunizations given in childhood or that their latent TB will remain latent.
Cases of health care workers inadvertently exposing thousands of patients to TB in New York City and Boston in recent years should serve as a warning to all health care facilities of the "tremendous potential for a bad outcome" when TB infection is left untreated, Sterling and Haas wrote recently in the New England Journal of Medicine.
In the New York case in 2003, a nurse from the Philippines who worked in a newborn nursery and maternity ward had pulmonary TB that went undiagnosed for two months. A decade earlier, a routine pre-employment TB skin test was positive, but the nurse declined treatment for latent TB, because she believed that the positive test was caused by an anti-tuberculosis vaccination (Bacille Calmette–Guérin, or BCG) and, therefore, most adults from the Philippines who had positive TB skin tests were not treated. About 1,500 people came in contact with the nurse while she was considered infectious, but only one-third could be located for follow-up, report Haas and Sterling. Among those located were at least four infants who were found to be infected with TB.
The Vanderbilt researchers wrote that treatment should be provided to health care workers with latent TB infection as indicated by a positive tuberculin skin test, particularly if they meet certain high-risk criteria. (See box below.)
High-risk criteria for latent TB treatment Persons in these high-risk groups should be given treatment for latent tuberculosis infection (LTBI) if: Reaction to the tuberculin skin test (TST) is ≥5 mm of induration:
Reaction to the TST is ≥10 mm of induration:
Source: Jenson et al. Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005. MMWR Recomm Rep. 2005; 54(RR17):1-141. |
Test for TB even in BCG-vaccinated
The CDC guidelines point out that many foreign-born people received the BCG vaccine, which is not commonly given in the United States due to the low rate of TB in this country. BCG may cause a positive reaction to the tuberculin skin test (TST), which may complicate decisions about prescribing treatment.
Despite this interference, the CDC guidelines specify that the tuberculin skin test (TST) and QuantiFERON-TB Gold test (QFT-G) are not contraindicated for persons who have been vaccinated with BCG. The presence or size of a TST reaction in these people does not predict whether BCG will provide any protection against TB disease, and the extent of a TST reaction in a BCG-vaccinated person is not a factor in determining whether the reaction is caused by latent TB (LTBI) or the prior BCG vaccination.
Treatment of LTBI substantially reduces the risk that TB infection will progress to disease, but the CDC warns that careful assessment must be made to rule out the possibility of TB disease before treatment for LTBI is started. Evaluation of TST reactions in persons vaccinated with BCG should be interpreted using the same criteria for those not BCG-vaccinated.
Q and A for the occ-health professional
The CDC's tuberculosis guidelines include a question-and-answer section to provide practical solutions for occupational health professionals. Following are some pertinent to the health care setting:
A health care worker (HCW) who has been vaccinated with BCG is being hired. She states that BCG will make her TST result positive and that she should not have a TST. Should this HCW be exempted from a baseline two-step TST?
Unless she has documentation of a positive TST result or previously treated LTBI or TB disease, she should receive baseline two-step TST or one BAMT (a blood assay for M. tuberculosis). Some persons who received BCG never have a positive TST result. For others, the positive reaction wanes after five years. U.S. guidelines state that a positive TST result in a person who received BCG should be interpreted as indicating LTBI.
Does BCG affect TST results and interpretations?
BCG is the most commonly used vaccine in the world. BCG might cause a positive TST (i.e., false-positive) result initially; however, tuberculin reactivity caused by BCG vaccination typically wanes after five years but can be boosted by subsequent TST. No reliable skin-test method has been developed to distinguish tuberculin reactions caused by vaccination with BCG from reactions caused by natural mycobacterial infections.
What steps should be taken when an HCW has had a recent BCG vaccination? When should the TST be placed?
A TST may be placed anytime after a BCG vaccination, but a positive TST result after a recent BCG vaccination can be a false-positive result. QFT-G should be used, because the assay test avoids crossreactivity with BCG.
Do health-care settings or areas in the United States exist for which a baseline two-step skin TST for newly hired HCWs is not needed?
Ideally, all newly hired HCWs who might share air space with patients should receive baseline two-step TST (or one-step BAMT) before starting duties. In certain settings, a choice might be offered not to perform baseline TST on HCWs who will never be in contact with or share air space with patients who have TB disease, or who will never be in contact with clinical specimens (e.g., telephone operators in a separate building from patients).
How long may I use my respirator for TB exposures before I discard it?
Respirators may be functional for weeks to months; reuse is only limited by considerations of hygiene, damage, and breathing resistance. A disposable respirator may be reused by the same HCW as long as it remains functional. Each respirator manufacturer has a recommended user seal-checking procedure that should be followed by the user each time the respirator is worn.
When does an infectious TB patient become noninfectious?
Historically, health care professionals have believed that the effect of anti-tuberculosis treatment to reduce infectiousness was virtually immediate; older texts state that patients on antituberculosis treatment are not infectious. No ideal test is available to diagnose the infective potential of a TB patient on treatment, and it is unlikely that infectivity disappears near the moment when anti-TB therapy is initiated. After two to three weeks of treatment, infectiousness averages less than 1% of the pretreatment level.
A pregnant HCW in a setting is reluctant to get a TST. Should she be encouraged to have the test administered?
Yes. Placing a TST on a pregnant woman is safe. The HCW should be encouraged to have a TST or offered BAMT. The HCW should receive education that 1) pregnancy is not contraindication to having a TST administered, and 2) skin testing does not affect the fetus or the mother. No documented episodes of TST-related fetal harm have been reported since the test was developed, and guidelines issued by the American College of Obstetrics and Gynecology emphasize that postponement of the application of a TST as indicated and postponement of the diagnosis of infection with M. tuberculosis during pregnancy is unacceptable.
A pregnant HCW in a setting has a positive TST result and is reluctant to get a chest radiograph. Should she be encouraged to have the chest radiograph performed?
Pregnant women with positive TST results or who are suspected of having TB disease should not be exempted from recommended medical evaluations and radiography. Shielding consistent with safety guidelines should be used even during the first trimester of pregnancy.
Are periodic chest radiographs recommended for HCWs (or staff or residents of long-term care facilities) who have positive TST or BAMT results?
No. Persons with positive TST or BAMT results should receive one baseline chest radiograph to exclude a diagnosis of TB disease. Further chest radiographs are not needed unless the patient has symptoms or signs of TB disease or unless ordered by a physician for a specific diagnostic examination. HCWs who have a previously positive TST result and who change jobs should carry documentation of the TST result and the results of the baseline chest radiograph (and documentation of treatment history for LTBI or TB disease, if applicable) to their new employers.
[For more information:
Trends in Tuberculosis — United States, 2005. MMWR 2006;55:305-308. Available on-line at www.cdc.gov/mmwr/preview/mmwrhtml/mm5511a3.htm.
Sterling TR, Haas DW. Transmission of Mycobacterium tuberculosis from health care workers. N Engl J Med 2006;355(2):118-21.]
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