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Open Access Highly Accessed Research article

Infrequent cross-transmission of Shigella flexneri 2a strains among villages of a mountainous township in Taiwan with endemic shigellosis

Ching-Fen Ko12, Nien-Tsung Lin13, Chien-Shun Chiou4, Li-Yu Wang5, Ming-Ching Liu6, Chiou-Ying Yang7 and Yeong-Sheng Lee89*

Author Affiliations

1 Institute of Medical Sciences, Tzu Chi University, No. 701, Zhongyang Rd., Sec. 3, Hualien 97004, Taiwan

2 The Third Branch Office, Centers for Disease Control, No. 20, Wenxin S. 3rd Rd., Taichung 40855, Taiwan

3 Master Program, Microbiology, Immunology, and Biochemistry, School of Medicine, Tzu Chi University, No. 701, Zhongyang Rd., Sec. 3, Hualien 97004, Taiwan

4 The Central Region Laboratory, Centers for Research, and Diagnostics, Centers for Disease Control, No. 20, Wenxin S. 3rd Rd., Taichung 40855, Taiwan

5 Department of Medicine, Mackay Medical College, No. 46, Sec. 3, Zhongzheng Rd., Sanzhi Dist., New Taipei City 25245, Taiwan

6 The Sixth Branch Office, Centers for Disease Control, No. 202, Sinsing Rd, Hualien 97058, Taiwan

7 Institute of Molecular Biology, National Chung Hsing University, No. 250, Kuo Kuang Rd., Taichung 40227, Taiwan

8 Department of Public Health, Tzu Chi University, No. 701, Zhongyang Rd., Sec. 3, Hualien 97004, Taiwan

9 The Fourth Branch Office, Centers for Disease Control, No. 752, Sec. 2, Datong Rd., Tainan 70256, Taiwan

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BMC Infectious Diseases 2013, 13:354  doi:10.1186/1471-2334-13-354

Published: 30 July 2013

Abstract

Background

Shigellosis is rare in Taiwan, with an average annual incidence rate of 1.68 cases per 100,000 persons in 2000–2007. However, the incidence rate for a mountainous township in eastern Taiwan, Zhuoxi, is 60.2 times the average rate for the entire country. Traveling between Zhuoxi’s 6 villages (V1–V6) is inconvenient. Disease transmission among the villages/tribes with endemic shigellosis was investigated in this study.

Methods

Demographic data were collected in 2000–2010 for epidemiological investigation. Thirty-eight Shigella flexneri 2a isolates were subjected to pulsed-field gel electrophoresis (PFGE) genotyping and antimicrobial susceptibility testing (AST).

Results

Fifty-five shigellosis cases were identified in 2000–2007, of which 38 were caused by S. flexneri 2a from 2000–2007, 16 cases were caused by S. sonnei from 2000–2003, and 1 case was caused by S. flexneri 3b in 2006. S. flexneri 2a caused infections in 4 of the 6 villages of Zhuoxi Township, showing the highest prevalence in villages V2 and V5. PFGE genotyping categorized the 38 S. flexneri 2a isolates into 2 distinct clusters (clones), 1 and 2. AST results indicated that most isolates in cluster 1 were resistant to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and trimethoprim-sulfamethoxazole (ACSSuX); all isolates in cluster 2 were resistant to ACSSuX and tetracycline. Genotypes were primarily unique to different villages or tribes. Tribe V2-1 showed the highest endemic rates. Eighteen isolates recovered from V2-1 tribe members fell into 6 genotypes, where 5 were the same clone (cluster 1). An outbreak (OB2) in 2004 in village V2 was caused by different clonal strains; cases in tribe V2-1 were caused by 2 strains of clone 1, and those in tribe V2-2 were infected by a strain of clone 2.

Conclusions

From 2000–2007, 2 S. flexneri 2a clones circulated among 4 villages/tribes in the eastern mountainous township of Zhuoxi. Genotyping data showed restricted disease transmission between the villages and tribes, which may be associated with difficulties in traveling between villages and limited contact between different ethnic aborigines. Transmission of shigellosis in this township likely occurred via person-to-person contact. The endemic disease was controlled by successful public health intervention.

Keywords:
Shigella; Molecular epidemiology; Disease transmission/control; Pulsed-field gel electrophoresis (PFGE); Antibiotic resistance