TUESDAY, Aug. 25 (HealthDay News) -- Increasingly, Salmonella ser Typhi bacteria strains isolated from typhoid fever cases in the U.S. are resistant to the standard antibiotics, and most of these drug-resistant cases appear to be contracted by U.S. citizens visiting India, according to a U.S. Centers for Disease Control and Prevention report in the Aug. 26 issue of the Journal of the American Medical Association.
Michael F. Lynch, M.D., of the CDC in Atlanta, and colleagues analyzed data on 1,902 U.S. citizens with typhoid fever from 1999 to 2006, and information on 2,016 S Typhi specimens forwarded to the CDC's National Antimicrobial Resistance Monitoring System Laboratory for susceptibility testing. The researchers evaluated the proportion of S Typhi bacteria isolates with resistance to antibiotics and assessed risk factors for resistant infections.
Of the S Typhi specimens evaluated, the investigators found that 272 (13 percent) were resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole, while 758 (38 percent) were resistant to nalidixic acid. Further, 734 (97 percent) of the isolates resistant to nalidixic acid also had decreased susceptibility to ciprofloxacin. The proportion of nalidixic acid-resistant isolates increased from 19 percent in 1999 to 54 percent in 2006. In addition, five ciprofloxacin-resistant isolates were identified.
"Infection with antimicrobial-resistant S Typhi strains among U.S. patients with typhoid fever is associated with travel to the Indian subcontinent, and an increasing proportion of these infections are due to S Typhi strains with decreased susceptibility to fluoroquinolones," the authors write.
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