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Vibrio increase concerns lead to risk assessment



There has been an increase in Vibrio outbreaks and presence in seafood has been known to disrupt trade, according to FAO and WHO.

The Food and Agriculture Organization of the United Nations (FAO) and World Health Organization (WHO) noted a rise in outbreaks and cases of foodborne disease attributed to pathogenic Vibrio species. As a result, there have been times where Vibrio spp. in seafood has disrupted international trade.

Food safety concerns with these microorganisms led to the need for a microbiological risk assessment to support risk management decision making for their control. Experts met to discuss risk assessment tools for Vibrio and seafood.

Vibrio outbreaks
There have been a series of outbreaks of Vibrio parahaemolyticus foodborne illnesses due to consumption of seafood. They have also occurred in regions where it was previously unreported, according to FAO and WHO.

Vibrio vulnificus can cause mild gastroenteritis in healthy people following consumption of raw bivalve mollusks. However, for those with chronic pre-existing conditions it can be a serious, often fatal, disease with one of the highest fatality rates of any foodborne bacterial pathogen.

In Asia, Vibrio parahaemolyticus is a common cause of foodborne disease. Outbreaks are normally small, involving fewer than 10 cases, but occur frequently. In Japan, from 2006 to 2008, there were 2,682 reported cases of infection. Boiled crabs caused one large outbreak, involving 691 cases.

Vibrio parahaemolyticus occurs in a variety of fish and shellfish, including clams, shrimp, lobster, crayfish, scallops, crabs, oysters and mussels.

When outbreaks of Vibrio parahaemolyticus and Vibrio vulnificus occur they are usually associated with seawater temperatures above 15 degrees C (59 degrees F) for the former and 20 degrees C (68 degrees F) for the latter.

Although thorough cooking destroys these microorganisms, oysters, mussels and other filter feeding shellfish are often eaten raw or lightly cooked.

Water temperature and salinity
Experts looked at monitoring options but noted final decision on the method selected will depend on purpose of the monitoring activity, cost, speed with which results are required and technical capacity of the laboratory.

Monitoring seawater for Vibrio parahaemolyticus and Vibrio vulnificus in bivalve growth and harvest areas has limited value to predict the presence of these pathogens in bivalves, according to the report.

Looking at seafood for these pathogenic vibrios was considered the most appropriate way to get insight into the levels of the pathogens in these commodities at the time of harvest.

Ongoing monitoring could be expensive, so a year-long study could be used to establish a relationship between total and pathogenic Vibrio parahaemolyticus and Vibrio vulnificus in seafood and factors such as water temperature and salinity. Once such a relationship is created for the harvest area of interest, measuring these factors may be a more cost-effective way of monitoring.

Quantitative risk assessments were developed in 2011 for Vibrio parahaemolyticus in oysters, finfish and bloody clams and for Vibrio vulnificus in oysters by FAO and WHO in 2005.

Post-harvest treatment technologies may reduce pathogenic vibrio but effectiveness will vary according to conditions of use, and there may be a need to balance getting the maximum possible reduction in bacterial content and retaining consumer-acceptance of the product or process.

Such methods include depuration, refrigerated storage, freezing, high pressure processing and mild heat treatment.

Experts considered the Joint FAO/WHO expert meetings on microbiological risk assessment (JEMRA) growth model for Vibrio vulnificus and the U.S. Food and Drug Administration model for Vibrio parahaemolyticus were appropriate for estimating growth in the American oyster but cannot be applied across all shellfish.

There are many variables for seafood such as practices during harvest and post-harvest and consumption that need to be considered in future modelling.

If a risk assessment model is to be commissioned it would be useful to have a database to compile information from worldwide on the variables relevant for the model.