An epidemiological study of outbreaks of Salmonella enterica serovar paratyphi A occurred in two Chinese families after traveled to different areas of China

摘要

We reported two familial clusters of paratyphoid fever after travel to China occurring in the same Yokohama ward from September to October 2002. Six Salmonella enterica serovar Paratyphi A (S. Paratyphi A) strains, 3 each from 2 clusters, were isolated and their characteristics analyzed using phage typing, susceptibility to antibiotics, and patterns of restriction endonuclease-digested DNA fragments in agarose gel following pulsed-field gel electrophoresis (PFGE). Mutations in genes for gyrA and parC, which determine sensitivity to fluoroquinolones, were also investigated. All isolates showed the same characteristics, i.e. "untypable", employing bacteriophages, resistant to antibiotics nalidixic acid and fosfomysin, and decreased susceptibility to fluoroquinolones. No difference was observed in PFGE patterns after digesting with 4 restriction enzymes, Xba I, Bin I, Spe I, and Xho I. We also found that the gyrA gene, which is one of the quinolone-resistance-determining regions (QRDR), was mutated at position 83 from serine to phenylalanine (from TTC to TCC) in all 6 strains. Other QRDR's, parC were not mutated commonly in them. Hearing from patients and family members, it was apparent that these 2 families had been contacted neither in Japan nor in China during ill or incubation period of paratyphoid fever, although a member of one cluster had a familial relationship with one of another family. It was also reported by them that typhoid fever is endemic in both of the areas of their visits. From these results, it was suggested that these 2 cluster cases were infected separately in China with the progeny of the same clone which is endemic in these regions.