Molecular typing of multiple-antibiotic-resistant Salmonella enterica serovar Typhi from Vietnam: Application to acute and relapse cases of typhoid fever

The rate of multiple-antibiotic resistance is increasing among Salmonella e nterica serovar Typhi strains in Southeast Asia. Pulsed-field gel electroph oresis (PFGE) and other typing methods were used to analyze drug-resistant and -susceptible organisms isolated from patients with typhoid fever in sev eral districts in southern Vietnam. Multiple PFGE and phage typing patterns were detected, although individual patients were infected with strains of a single type. The PFGE patterns were stable when the S. enterica serovar T yphi strains were passaged many times in vitro on laboratory medium. Paired S. enterica serovar Typhi isolates recovered from the blood and bone marro w of individual patients exhibited similar PFGE patterns. Typing of S. ente rica serovar Typhi isolates from patients with relapses of typhoid indicate d that the majority of relapses were caused by the same S. enterica serovar Typhi strain that was isolated during the initial infection. However, some individuals were infected with distinct and presumably newly acquired S. e nterica serovar Typhi isolates.