Drug-Resistant Tuberculosis in New York City

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Abstract
In their article on drug-resistant tuberculosis in New York City, Frieden et al. (Feb. 25 issue)1 demonstrate that cases of such disease are cause for serious concern. I wonder, however, whether the authors studied a representative population of patients. The survey population consisted of patients who had a positive culture for Mycobacterium tuberculosis during April 1991. Such a survey represents neither incidence nor prevalence. Like autopsy studies, laboratory-based surveys are subject to selection bias and may oversample patients with severe morbidity. Patients with treatment failure, relapse, or drug resistance are more likely to undergo serial drug-susceptibility testing than patients who respond to therapy or have drug-susceptible disease. Such possible bias is suggested by the fact that the majority of study patients with isolates available for testing (239 of the 466 patients) were reported to have previously received treatment. What proportion of the total number of cases of tuberculosis in New York City that were reported to the Centers for Disease Control and Prevention during this period was included in the study? What proportion of patients in the city's tuberculosis registry in April 1991 was included? How did patients with tuberculosis who were included in the study compare with those who were not, in terms of demographic and clinical characteristics?