Confirmation of Homologous Strains as the Cause of Bacillary Dysentery Outbreaks in Nanjhuang Township of Miaoli County and Heping Township of Taichung County by Molecular Epidemiology
2006 Vol.22 NO.7
Between Nov. 18 and Dec. 5 in 2005, an outbreak of bacillary dysentery caused by Shigella sonnei occurred in Nanjhuang Township of Miaoli County. Twelve cases were identified (asymptomatic positive rate was 8.3%). Cases included the index case, his/her family members, his/her neighbors and relatives of the neighbors, with an infection rate of 14.5% (12/83). Between Jan. 1 and 23 in 2006, an outbreak caused by S. sonnei also occurred in Heping Township of Taichung County. Five positive cases were indentified, including the index case, his/her classmates and their family members, and the director of the class, with an infection rate of 14.7% (5/34). The average infection rate of the two outbreaks was 14.5%, and the positive rate of water specimens was 0% (0/82). Since the two outbreaks had close temporal and spatial relationships, pulsed-field gel electrophoresis was used to analyze the DNA fingerprint maps of isolated strains, the results of which suggested that the strains in the two outbreaks were homologous. Subsequent disease surveillance also confirmed the relationship between these two outbreaks: that is, the outbreak occurred in Heping Township was related to two infected cases in Nanjhuang Township. We suspected that the two cases brought the bacteria to Heping Township, leading to subsequent transmissions by contact. Comparing with the Shigella DNA fingerprint map database of the CDC, the strains in the two outbreaks were most closely related to strains from Indonesia.