Epidemiological Investigation of Salmonella enterica Serovar Kedougou in Thailand

Objective: Salmonella enterica serovar Kedougou is among the top 10 serovars reported in northern Thailand. The objective of this study was to identify risk factors associated with Salmonella Kedougou infection in Thailand and to compare the molecular types and antimicrobial resistance with Salmonella Kedougou isolates of human origin from United States and of animal origin from the United Kingdom.

Methods: Data from 13,976 Salmonella infections of which 253 were Salmonella Kedougou collected in Thailand between 2002 and 2008 were analyzed by logistic regression. Antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE) were performed on selected Salmonella Kedougou strains causing infections in Thailand (n = 66), and compared to isolates from the United States (n = 5) and the United Kingdom (n = 20).

Results: Logistic analysis revealed season (hot/dry; p = 0.023), region (northern Thailand; p <0.001), and specimen (stool; p <0.001) as significant risk factors associated with Salmonella Kedougou infection compared to other nontyphoid Salmonella. Of the Salmonella Kedougou isolates of human origin, 84% exhibited resistance to at least three antimicrobial classes.

Three strains recovered from human stool in Thailand were resistant to third-generation cephalosporins: two harbored blaCTX-M-63 and one blaCMY-2. PFGE revealed 45 unique clusters. Isolates obtained from humans in Thailand and the United States presented identical PFGE profiles suggesting a travel association, whereas the majority of the animal isolates from United Kingdom clustered separately.

Conclusions: This study reveals Salmonella Kedougou as a major cause of human infections in northern Thailand especially during the hot period and suggests a global spread probably due to travel. The clonal types causing infections in humans differed from those observed in animals in United Kingdom, which suggests the absence of an epidemiological link and could suggest differences in virulence.

The high frequency of antimicrobial resistance, including emergence of resistance to fluoroquinolones and third-generation cephalosporins, might pose problems for treatment of infections.