Increasing fluoroquinolone resistance in Salmonella typhi in Ontario, 2002-2007.

We reviewed the antibiotic susceptibility patterns of all isolates of Salmonella typhi in Ontario, Canada from January 2002 to December 2007. We identified a total of 381 unique cases over the 5-year period (50-73 cases per year). Of the 381 cases, 171 were female, 164 were male, and no gender was identified for 33 cases. Age of the patients ranged from less than 1 to 102 years of age (median age of 20 years). Although resistance patterns for ampicillin, trimethoprim-sulfamethoxazole, third generation cephalosporins (cefotaxime until May 2005 and ceftriaxone from June 2005 to present), and chloramphenicol remained stable, nalidixic acid resistance rose sharply between 2003 and 2005 and has remained at approximately 80% of isolates since 2005. The significant and sustained increase in nalidixic acid-resistant S. typhi suggests that ciprofloxacin should no longer be used as the drug of choice for the empiric treatment of typhoid fever in Ontario.