A report from the United States confirmed that paratyphoid fever most often was caused by nalidixic acid-resistant S. paratyphi A, and like typhoid fever,

was usually acquired while traveling internationally. In this observation, infection with S. paratyphi A was associated with travel to selleck chemical South and Southeast Asia, and nalidixic acid-resistant infection was associated with travel to South Asia [20]. PFGE is currently the method for the subtyping of sporadic or epidemic Salmonella isolates. By the use of a standardized PFGE protocol in this study, the PulseNet protocol, all isolates of S. paratyphi A were assigned to type A, subtype A1 or A2, which suggests endemic disease from the presence of a single clone over 6-year period. By investigating 62 medical records of inpatients infected www.selleckchem.com/products/citarinostat-acy-241.html by S. paratyphi A, it was confirmed that five patients infected by S. paratyphi A had traveled to other domestic cities or regions, and one had traveled internationally to Bangladesh. Our data also suggests that the same clone of S. paratyphi A was present in China over the study period. An outbreak of paratyphoid fever associated with S. paratyphi A in New Delhi, India was investigated by PFGE [21]. The five

sporadic isolates of S. paratyphi A gave PFGE patterns following XbaI digestion that were distinct, with differences of 8 to 12 bands. In contrast, the 13 outbreak isolates shared only four closely related PFGE patterns differing only in 1 to 6 bands. Similar results were obtained after digestion with a second restriction endonuclease, SpeI. In another study, a total of the 39 human isolates of S. paratyphi A from Pakistan, India, Indonesia and Malaysia were typed by PFGE using XbaI restriction digests. This study suggested that a limited number of clones were responsible for paratyphoid fever in those countries [22]. Similarly,

the high proportion of S. paratyphi A infection in Nepal during 2001 was due to the emergence of a single clone [23]. In a recent report by Gupta et al [20], 110 isolates of S. paratyphi A were typed by PFGE of XbaI and BlnI restriction digests, which were obtained from patients with paratyphoid fever in the United States from 2005 to 2006. Thirty-one molecular subtypes (unique combinations of XbaI and BlnI patterns) were identified, and six subtypes (19%) accounted for 90 (82%) of these isolates. Conclusions Nalidixic acid-resistant S. typhi and S. paratyphi A blood isolates were highly prevalent in Shenzhen, China. PEGF showed the variable genetic diversity of nalidixic acid-resistant S. typhi and limited genetic diversity of nalidixic acid-resistant S. paratyphi A that suggests a clonal expansion of S. paratyphi A infection in the community. Acknowledgements The authors express sincere appreciation to Xiaolu Shi and Quanxue Lan for their guidance in PFGE typing. We thank Dr. Lance R. Peterson for helpful comments on our manuscript.