Department: CLINICAL QUERIES: Global Insights
Elizabeth Heavey is the RN-BSN program director and an associate professor of nursing at The College at Brockport, State University of New York, in Brockport, N.Y. Dr. Heavey is also a member of the editorial board of Nursing2013.
The author has disclosed that she has no financial relationships related to this article.
I'm an RN originally from the Ukraine, where I received the bacille Calmette-Guérin (BCG) vaccine as a child over 30 years ago. When I came to the United States 4 years ago, I had a positive (22 mm) tuberculin skin test (TST) with purified protein derivative (PPD) and a negative chest X-ray. I was told not to have any more TSTs. When I applied to an RN-to-BSN program, however, I learned that I should also be treated for latent tuberculosis (TB) infection (LTBI). I've never had any TB signs or symptoms and don't understand why I should be treated.—M.N., PA.
Elizabeth Heavey, PhD, RN, CNM, replies: Because the BCG vaccine contains Mycobacterium bovis, it doesn't protect against TB infection with M. tuberculosis.1 However, it offers some protection against certain childhood complications of active TB disease, such as miliary TB and TB meningitis.2 Although the BCG vaccine generally isn't used in the United States, it's still administered in parts of the world with high prevalence of TB.
Most adults with a childhood history of receiving the BCG vaccine will have a positive TST—not because of the vaccination, but because they've been exposed to TB; in other words, they have LTBI.3 They were exposed to and infected with TB, but their immune responses have so far prevented active disease from developing.1
Patients who've received the BCG vaccine have an increased likelihood of a false-positive TST when they're screened for TB. However, the chance of having a false-positive response 5 to 10 years after vaccination, particularly a response greater than 10 to 14 mm, is very low.3
Although patients with LTBI don't have active disease and can't infect anyone else, the CDC recommends treating them regardless of BCG status, particularly those in high-risk groups, to prevent LTBI from progressing to active disease.1 Conversion from latent infection to active disease is one of the major factors contributing to the presence of TB in low-endemic countries such as the United States.1
In patients with LTBI, the immune response must remain strong to prevent active disease. Changes in immune status related to medication, disease processes, or even pregnancy or aging put the infected patient at risk for development of active disease.
An estimated 5% to 10% of those with LTBI eventually experience a conversion to active disease.4 For most, this occurs 6 to 18 months after the initial infection.
Those who've had the BCG vaccine and a positive TST may want to consider a blood test for TB called the interferon-gamma release assay. It's available in two FDA-approved commercial forms, with a sensitivity (ability to correctly identify those with the disease as having the disease) of up to 96% among patients vaccinated with BCG.5 The blood test is the gold standard for determining TB infection status among those who've received the BCG vaccine.5 A positive test result indicates exposure to and infection with M. tuberculosis, but distinguishing between LTBI and active disease requires additional testing.
Anyone with LTBI who begins treatment with corticosteroids, chemotherapy, or other immunosuppressants is at an increased risk of conversion to active disease.3 Nurses should share their LTBI status with their primary care providers and discuss completing a full course of treatment to prevent the conversion to active disease.6 Large-scale community investigations have followed nurses who converted to active disease status and exposed patients, coworkers, and others. One such case resulted in 900 patients, 613 infants, and 32 coworkers exposed by one maternity nurse.7
Completing a full course of treatment for LTBI not only prevents active TB but also prevents resistant strains of TB from developing. Patients who don't complete treatment for LTBI may later develop active TB disease resistant to the drug used. These patients are extremely difficult to treat and require extensive monitoring.3
2. Wertheim HFL, Horby P, Woodall JP. Atlas of Human Infectious Diseases. Chichester, UK: Wiley-Blackwell; 2012.
4. CDC. Recommendations for use of an isoniazid-rifapentine regimen with direct observation to treat latent Mycobacterium tuberculosis infection. MMWR Morb Mortal Wkly Rep. 2011;60(48):1650–1653.
5. Dyrhol-Riise AM, Gran G, Wentzel-Larsen T, Blomberg B, Haanshuus CG, Mørkve O. Diagnosis and follow-up of treatment of latent tuberculosis: the utility of the QuantiFERON-TB Gold In-tube assay in outpatients from a tuberculosis low-endemic country. BMC Infect Dis. 2010;10:57.
6. Horsburgh CR Jr, Goldberg S, Bethel J, et al. Latent TB infection treatment acceptance and completion in the United States and Canada. Chest. 2010;137(2):401–409.
7. Todd B. Are you 'PPD positive'? Am J Nurs. 2012;112(4):53–55.
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