Epidemiologic study of Shigella sonnei from sequential outbreaks and sporadic cases using different typing techniques

Area of Science:

• Microbiology
• Epidemiology
• Infectious Diseases

Background:

• Eight sequential outbreaks of Shigella sonnei occurred in Aichi Prefecture, Japan (Oct 1992-June 1993).
• The source of these outbreaks remained unknown, necessitating epidemiological investigation.

Purpose of the Study:

• To subtype Shigella sonnei isolates from the Japanese outbreaks.
• To compare the efficacy of different subtyping methods for Shigella sonnei.
• To investigate the epidemiological links between outbreak strains and sporadic isolates from travelers.

Main Methods:

• Analysis of 53 outbreak-related Shigella sonnei isolates.
• Comparison of subtyping techniques: plasmid typing, pulsed-field gel electrophoresis (PFGE), colicin typing, and antimicrobial susceptibility testing.
• Examination of 58 sporadic Shigella sonnei isolates from international travelers.

Main Results:

• Pulsed-field gel electrophoresis (PFGE) and plasmid typing were superior to colicin typing and antimicrobial susceptibility testing for Shigella sonnei subtyping.
• PFGE analysis identified four genetically related isolates responsible for the eight sequential outbreaks.
• Some sporadic isolates from travelers in Asia shared genetic similarities with the outbreak strains.

Conclusions:

• Genetically related Shigella sonnei isolates were prevalent in Asia during 1992-1993.
• The extensive movement of people and food likely contributed to the spread of these genetically related strains.
• DNA-based subtyping methods are crucial for effective outbreak investigation and control of infectious diseases.