Genotypic analysis of Salmonella enterica serovar Typhi collected during two successive autumnal typhoid outbreaks in southeast Tunisia


N. Ben Saidaa, S. Mhallaa, N. Bouzouïab, J. Boukadidaa


Objective: Investigation of two successive autumnal outbreaks of typhoid fever that occurred in southeast Tunisia.

Patients and methodsSalmonella typhi isolates collected from confirmed cases of typhoid fever during the two outbreaks occurred in autumn 2004 and 2005 and from healthy carriers were analyzed by antibiogram and pulsed-field gel electrophoresis (PFGE).

Results: A total of 86 isolates of Salmonella enterica serovar Typhi (76 from blood culture or stool of patients involved in both outbreaks and 10 from stool of healthy carriers) were obtained. All isolates of S. typhi were fully sensitive to all antibiotics tested, particularly to co-trimoxazole and ciprofloxacin. All isolates of 2004 (39 from patients and 10 from healthy carriers) appeared to be genetically identical when digested with SpeI, AvrII and XbaI. XbaI digestion of 2005 outbreak isolates gave five different patterns with predominance of the 2004 outbreak pattern. Both outbreaks were concomitant with the season of “legmi”, fermented juice traditionally extracted from palm-tree.

Conclusion: PFGE with XbaI was discriminatory and can be useful for epidemiological routine investigation of typhoid fever. Typing results suggests the monoclonality of 2004 outbreak and the multiclonality of the 2005 outbreak. The epidemic clone of S. typhi is able to persist for long period in a quiet state in the population and to give again a new outbreak, when the conditions become favorable.


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