LETTER
Tuberculin Booster Reactions and Conversions
William W. Stead, MD
1 September 1994 | Volume 121 Issue 5 | Pages 387-388
TO THE EDITOR:
In their article, Menzies and colleagues [1] misquote me as defining a "booster" reaction as being at least 12 mm greater than a previous negative test result. Actually, we defined a tuberculin "conversion" as an increase of at least 12 mm greater than the size of the initially negative two-step test result some months later, particularly if patients had recently been exposed to tuberculosis. We view any lesser increase in size as a booster [2]. Our intent was to emphasize that small increases in the size of subsequent tuberculin test reactions generally do not signify new infections, which would require a course of preventive chemotherapy (usually isoniazid) [3].
The term "booster"-positive is generally used to refer to a positive tuberculin test result (induration, 
10 mm) obtained by a second application of 5U of tuberculin 1 to 3 weeks after an initial negative test result. In our report, we attempted to provide a practical distinction between a "booster-positive" result and a true "conversion." Subsequently, the Advisory Council for the Elimination of Tuberculosis of the Centers for Disease Control and Prevention picked up on our observation and, to reduce confusion, defined a conversion in the elderly as an increase of "at least 15 mm" over a previously negative two-step test result [4]. Several authors have shown that minor increases in the size of the reaction are unstable and are unlikely to be caused by a recent infection.
1. Menzies R, Vissandje B, Rocher E, St. Germain Y. The booster effect in two-step tuberculin testing among young adults in Montreal. Ann Intern Med. 1994; 120:190-8.
2. Stead WW, To T. The significance of the tuberculin skin test in elderly persons. Ann Intern Med. 1987; 107:837-42.
3. Stead WW, To T, Harrison RW, Abraham JH 3d. Benefit-risk considerations in preventive treatment for tuberculosis in elderly persons. Ann Intern Med. 1987; 107:843-5.
4. Centers for Disease Control and Prevention. Prevention and control of tuberculosis in facilities providing long-term care to the elderly. Recommendations of the Advisory Committee for Elimination of Tuberculosis. MMWR Morb Mortal Wkly Rep. 1990; 39:1-20.
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