Quinolone-Resistant Salmonella typhi in Viet Nam: Molecular Basis of Resistance and Clinical Response to Treatment

Nalidixic acid ‐ resistant Salmonella typhi (NARST) was first isolated in Viet Nam in 1993. Analysis of the quinolone resistance-determining region of gyrA in 20 NARST isolates by polymerase chain reaction and single-stranded conformational polymorphism yielded two novel patterns: pattern II corresponding to a point mutation at nucleotide 87 Asp r Gly (nA 17), and pattern III corresponding to a point mutation at nucleotide 83 Ser r Phe (n A 3). In trials of short-course ofloxacin therapy for uncomplicated typhoid, 117 (78%) of 150 patients were infected with multidrug-resistant S. typhi, 18 (15%) of which were NARST. The median time to fever clearance was 156 hours (range, 30 ‐ 366 hours) for patients infected with NARST and 84 hours (range, 12 ‐ 378 hours) for those infected with nalidixic acid ‐ susceptible strains (P o .001). Six (33.3%) of 18 NARST infections required retreatment, whereas 1 (0.8%) of 132 infections due to susceptible strains required retreatment (relative riskA 44; 95% confidence intervalA 5.6 ‐ 345; Po .0001). We recommend that short courses of quinolones not be used in patients infected with NARST.