Emergence of trimethoprim-sulfamethoxazole resistance in the AIDS era

Trimethoprim-sulfamethoxazole (TMP-SMX) is widely used for Pneumocystis car inii pneumonia prophylaxis in human immunodeficiency virus (HIV)-infected p atients, but little is known about the effects of this practice on the emer gence of TMP-SMX-resistant bacteria. A serial cross-sectional study of resi stance to TMP-SMX among all clinical isolates of Staphylococcus aureus and 7 genera of Enterobacteriaceae was performed at San Francisco General Hospi tal. Resistance among all isolates was <5.5% from 1979 to 1986 but then mar kedly increased, reaching 20.4% in 1995, This was most prominent in HIV-inf ected patients: resistance increased from 6.3% in 1988 to 53% in 1995, The largest increases in resistance were in Escherichia coli (24% in 1988 to 74 % in 1995) and S. aureus (0% to 48%) obtained from HIV-infected patients. A rapid increase in the use of prophylactic TMP-SMX in HIV disease was also observed during this time in San Francisco and is likely responsible for th e increase in TMP-SMX resistance.