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Introduction and spread of multi-resistant Shigella dysenteriae I in Thailand
D N Taylor1, L Bodhidatta, J E Brown
1Department of Bacteriology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
Abstract:
Outbreaks of Shigella dysenteriae I occurred in northeastern Thailand in the fall of 1986 and again in the spring and fall of 1987 for the first time in over 20 years. The epidemic strain of S. dysenteriae I was resistant to tetracycline, streptomycin, chloramphenicol, and trimethoprim-sulfamethoxazole, but susceptible to ampicillin. Trimethoprim resistance was chromosomally encoded by type I dihydrofolate reductase. In Ubon Province, where 10,000 cases of dysentery were reported, there were 3-5 cases of dysentery per 1,000 residents during the peak months, with 2-5 hospitalizations per 100 cases of reported dysentery. There were 2 deaths among 101 hospitalized, culture-confirmed cases. The overall case-fatality rate among reported cases of dysentery in this province was 0.9%. In contrast to S. flexneri infections, which occurred predominantly among children less than 5 years old, S. dysenteriae I infections occurred in all age groups. The large number of susceptibles appeared to be important in allowing rapid spread of S. dysenteriae I. In 1 village, 46% of 434 villagers reported dysentery; S. dysenteriae I was isolated from 24 out of 81 (30%) individuals cultured. Based on the prevalence of IgG antibody to S. dysenteriae I lipopolysaccharide, it was estimated that 76% of the villagers had been infected.
Insights
Shigella dysenteriae I outbreaks in Thailand showed a drug-resistant strain. High infection rates occurred across all ages, highlighting the importance of susceptible populations in disease spread.
Area of Science:
- Epidemiology
- Infectious Diseases
- Microbiology
Background:
- Recurrent outbreaks of Shigella dysenteriae serotype I (S. dysenteriae I) occurred in northeastern Thailand in 1986 and 1987, marking the first emergence in over two decades.
- The prevalent epidemic strain exhibited resistance to multiple antibiotics, including tetracycline, streptomycin, chloramphenicol, and trimethoprim-sulfamethoxazole, while remaining susceptible to ampicillin.
Purpose of the Study:
- To investigate the epidemiology and characteristics of the S. dysenteriae I outbreaks in northeastern Thailand.
- To determine the antibiotic resistance patterns and genetic basis of trimethoprim resistance in the epidemic strain.
- To assess the clinical impact, including incidence, hospitalization, and case-fatality rates, and identify factors contributing to the rapid spread.
Main Methods:
- Surveillance data collection on dysentery cases in Ubon Province.
- Antimicrobial susceptibility testing of the S. dysenteriae I epidemic strain.
- Molecular characterization of trimethoprim resistance, identifying type I dihydrofolate reductase.
- Serological surveys using IgG antibody to S. dysenteriae I lipopolysaccharide to estimate infection prevalence.
Main Results:
- In Ubon Province, 10,000 dysentery cases were reported, with an incidence of 3-5 per 1,000 residents during peak months and a 0.9% overall case-fatality rate among reported cases.
- The epidemic S. dysenteriae I strain was resistant to tetracycline, streptomycin, chloramphenicol, and trimethoprim-sulfamethoxazole, with trimethoprim resistance encoded by type I dihydrofolate reductase.
- Infections affected all age groups, unlike S. flexneri, and a village study indicated high attack rates (46%) and infection prevalence (76% estimated by serology).
Conclusions:
- The re-emergence of S. dysenteriae I in Thailand was driven by a multi-drug resistant strain.
- The susceptibility of the broader population across all age groups facilitated the rapid dissemination of the pathogen.
- Effective control strategies must consider the antibiotic resistance profile and the widespread susceptibility within the population.