Characteristics of a sharp decrease in Vibrio parahaemolyticus infections and seafood contamination in Japan.

Area of Science:

• Food Microbiology
• Foodborne Pathogens
• Bacteriology

Background:

• Vibrio parahaemolyticus has been a significant foodborne pathogen in Japan since the 1960s.
• A major epidemic caused by pandemic serotype O3:K6 occurred from 1997 to 2001.
• V. parahaemolyticus infections have notably decreased since the early 2000s.

Purpose of the Study:

• To investigate the reasons behind the sharp decline in V. parahaemolyticus infections in Japan.
• To analyze the trends in seafood contamination by V. parahaemolyticus and its pathogenic strains.
• To determine the relationship between seafood contamination and the reduction in human infections.

Main Methods:

• Analysis of serotypes from 977 V. parahaemolyticus outbreaks.
• Detection of total and pathogenic (tdh gene-positive) V. parahaemolyticus in 842 seafood samples.
• Molecular analysis including tdh-PCR, group-specific PCR, and pulsed-field gel electrophoresis (PFGE) of isolates from patients and seafood.

Main Results:

• A significant decrease in V. parahaemolyticus infections was observed for O3:K6 and other serotypes starting in 1999.
• Seafood contamination by tdh-positive V. parahaemolyticus decreased by only one-fourth between 2001 and 2007-2009, a small reduction compared to the 18-fold drop in outbreaks.
• The pandemic O3:K6 serotype with a consistent PFGE profile was detected in seafood and patients throughout the study period, indicating persistent contamination.

Conclusions:

• The decline in V. parahaemolyticus infections is likely unrelated to changes in seafood contamination levels from production to distribution.
• Persistent contamination of seafood with pathogenic V. parahaemolyticus, including the O3:K6 serotype, suggests that control measures after the distribution stage may be crucial.
• Future prevention efforts for V. parahaemolyticus infections should consider interventions beyond the wholesale market level.