To the Editor.
—The beautiful demonstration by Dr Frieden and colleagues1 that transmission of a single strain of Mycobacterium tuberculosis accounted for much of the recent increase in multidrug-resistant tuberculosis (TB) in New York City raises the question of the generalizability of this finding to other cities.We perform drug susceptibility testing on approximately 180 isolates each year in our clinical microbiology laboratory, located in a tertiary care referral center in Mexico City. Between January 1990 and December 1991, 178 initial isolates from 178 patients referred from Mexico's National Institutes of Health were tested for resistance to 9 antibiotics using the Bactec system (Becton: Dickerson, Cockeyville, Md). Although this is not a systematic sampling for TB in Mexico City, it included isolates from a wide variety of settings, including 26 cases infected with human immunodeficiency virus (HIV). Of these 178 isolates, 40 were resistant to isoniazid and rifampin. Knowing
de Leon AP, Small PM, Sifuentes-Osornio J. Highly Drug-Resistant Tuberculosis. JAMA. 1997;277(8):628-629. doi:10.1001/jama.1997.03540320030027