© 2006 American Thoracic Society
The Scope and Impact of Treatment of Latent Tuberculosis Infection in the United States and CanadaTo the Editor:The recent article by Sterling and colleagues (1) regarding treatment of latent tuberculosis infection (LTBI) most likely overestimates the impact of such treatment, because it was based on a questionable assumption taken from an earlier article written by a coauthor of the current article, Dr. Horsburgh (2). In the earlier article, Horsburgh states: "The lifetime risk of reactivation tuberculosis (TB) was assumed to decrease for the first nine years after skin-test conversion and then to continue to decrease at a rate of 10% per decade—a rate that is consistent with the reported decreases in skin-test reactivity" (2). By contrast, two 20-year studies (3, 4) have shown that among tuberculin reactors with normal chest X-rays, who were not identified as recent converters, reactivation rates decreased much more rapidly in two decades: 54.8% in a Centers for Disease Control (CDC) study (3) and 94.6% 80.5%, and 90% in three groups in a Medical Research Council (MRC) study (4) (Table 1).
While TB rates are considerably higher in elderly persons (5), it is not known how much of this is potentially preventable by LTBI treatment given earlier in the patient's life because the introduction of tubercle bacilli occurred before LTBI treatment or is not preventable because tubercle bacilli were acquired for the first time after LTBI treatment or by exogenous reinfection (6). When all factors are taken into consideration, it is highly probable that the rates of reactivation fall much more rapidly than 10% per decade after the first 9 years following tuberculin conversion, at least until the person reaches the later years of life. If so, the benefit from LTBI treatment and the nationwide impact is considerably lower than that estimated by the authors.
These comments are not meant to discourage the use of LTBI treatment for persons who have a significantly increased risk of developing TB, such as children, definite converters, contacts of active cases, those with HIV infection or old, healed tuberculosis, and patients taking anti–tumor necrosis factor-
Harbor UCLA Medical Center, Torrance, California FOOTNOTES Conflict of Interest Statement: T.M. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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therapies.