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U.S. Department of Health and Human Services

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Backgrounder on Measures to Eliminate Risk Caused by Vibrio vulnificus Infection from Consumption of Raw Molluscan Shellfish

On October 17, 2009, FDA announced its intention to inform seafood producers of the need to take measures that will largely eliminate the risk of death and disease caused by Vibrio vulnificus (Vv) infection from consumption of raw molluscan shellfish (e.g., oysters and clams). The announcement was made at the biennial meeting of the Interstate Shellfish Sanitation Conference (ISSC) in Manchester, New Hampshire. The ISSC includes representatives of the shellfish industry as well as representatives of the FDA and other government agencies.

What is Vibrio vulnificus?

Vibrio vulnificus is a naturally occurring bacterium in the same family as those that cause cholera. Vv can be found in warm coastal waters, especially the Gulf of Mexico between the months of April and October. The level of Vv in Gulf of Mexico oysters greatly increases during warm weather months, resulting in the annual occurrence of illnesses in consumers who eat oysters raw. V. vulnificus can infect the bloodstream, causing a severe and life-threatening illness characterized by fever and chills, decreased blood pressure (septic shock), and blistering skin lesions. V. vulnificus bloodstream infections are fatal about 50% of the time. Generally, 15 deaths per year result from Vv infection associated with the consumption of raw Gulf Coast oysters. At greatest risk are individuals whose immune systems have been compromised or have certain health conditions, such as: chronic alcohol abuse; liver, stomach, or blood disorders; cancer; AIDS; diabetes; or kidney disease. Many of these individuals do not know that they are predisposed to V. vulnificus infection.

What has been done nationally to date to reduce the risk of Vv?

The FDA has worked with the Interstate Shellfish Sanitation Conference for more than a decade to monitor and reduce Vv contamination. In 2001 the Interstate Shellfish Sanitation Conference adopted a seven-year plan designed to reduce illness from Vibrio vulnificus infection by 60%. If this reduction could not be achieved through voluntary means, the states would mandate post-harvest processing of raw oysters by industry or other measures to reduce the risk of illness. Between 2001 and 2008, the FDA, the ISSC, and a number of State agencies undertook an extensive consumer education campaign about the risk of raw oyster consumption aimed primarily at at-risk individuals. Efforts were also made to foster voluntary adoption by the industry of technologies that eliminate this pathogen while preserving the sensory qualities of the raw product, called post-harvest processing (PHP).  Although consumer studies have demonstrated modest increases in consumer awareness of the Vv risk by the at-risk population, there is little to suggest that there has been a significant change in consumption behavior.

Recent CDC data show there has been essentially no change in the number of Vibrio vulnificus infections or deaths resulting from consumption of raw oysters in those states that permitted the sale of untreated Gulf Coast oysters during the warm months. These data clearly demonstrate that sustained education efforts and voluntary adoption of PHP have not had the intended public health results.

There is evidence that controls that were designed to reduce, but fall well short of eliminating, the risk of Vibrio illness such as implementation of a five-hour time from harvest to refrigeration also have not been effective. While such controls were in effect for most of the 2008 Vibrio risk season, there has not been a significant decline in the numbers of Vv illnesses reported in that year as compared to previous years. This could be the result of difficulties in enforcement of this type of control, natural year-to-year variability in illness numbers, or other factors.

What technologies exist to prevent Vv?

Post harvest processing (PHP) involves the use of technologies that virtually eliminate the Vibrio pathogens but retain the sensory qualities of raw product. These technologies, developed by industry, academia, and government (with support of the ISSC), include low temperature heat, individual quick freezing with frozen storage, high hydrostatic pressure, and low-dose gamma irradiation. All of these technologies have been validated to reduce extremely high levels of the pathogen to nondetectable levels. Based in part on research performed by FDA, the oyster industry began use of PHP to control the risk of Vv in the mid 1990s. PHP is economically feasible and is already being used on 15% of half-shell oyster production in the Gulf of Mexico region, but the costs and disruption to the industry to implement PHP technology will be greater, especially for some small producers, than those envisioned as a result of previous ISSC-endorsed strategies.

Is PHP required anywhere?

Yes. In 2003, the State of California required PHP for the high-risk Gulf Coast oysters during the summer months and since that time has experienced no Vibrio illnesses or deaths (an investigation is on-going that will likely link an illness in California this year to PHP oysters). Between 1991 and 2001, prior to PHP being required, it reported 40 Vibrio deaths.

In addition, many safety-conscious retailers, such as Legal Sea Foods and Costco, only sell Gulf Coast oysters that have been post-harvest processed.

In response to its audit of the U.S. system for the control of molluscan shellfish safety, the European Union (EU) insisted on assurance from FDA that Gulf Coast product would not be exported to the EU during the at-risk season unless the risk of Vv was mitigated by measures such as PHP.

What action is FDA intending that processors take now to reduce death and disease from Vv and Vp?

FDA believes that additional controls need to be put in place, particularly in light of the availability of demonstrably effective and feasible PHP methods, and the failure of other measures to achieve the purpose of the HACCP regulation. The Agency believes that application of PHP, or other equally effective controls, is the appropriate preventive measure under the regulation for the control of V. vulnificus in shellfish when the hazard is reasonably likely to occur. It does not believe measures that reduce, but fall well short of eliminating the hazard, such as improvements in refrigeration, are sufficient to meet the purpose of the regulation, especially given the availability of PHP technologies.

Therefore, the Agency intends to modify its guidance to the industry on the implementation of the Seafood HACCP Regulation, the “Fish and Fishery Products Hazards and Controls Guidance,” such that implementation of PHP or equivalent measures would be achieved for the control of V. vulnificus by the beginning of the risk season in 2011. These technologies can virtually eliminate this hazard while preserving the sensory qualities of raw product.

Implementation of FDA’s policy will substantially reduce and possibly eliminate these deaths and is justified as well by the fact that previous risk reduction measures tried over the last 7 years by the ISSC have failed.

What costs will this impose on the industry, and what will FDA do to help them?

The Agency recognizes that this action will have an economic impact on processors, particularly small ones. According to a re-analysis of data from a 2000 Research Triangle Institute study, it costs three to four cents per half-shell oyster to use high-hydrostatic or warm water pasteurization PHP measures and about thirteen cents per half-shell oyster for IQF frozen product. But these numbers don’t tell the whole story. Each of these processes offer its own set of trade-related benefits, including the ability to harvest oysters when they are in prime condition and market them when natural stocks are of lower quality; long-term frozen shelf-life; and elimination of the need for a skilled shucker in the case of shucked PHP product. The elimination of the need for a skilled shucker for product treated with hydrostatic pressure actually results in a cost savings, primarily to restaurants, per oyster over untreated shucked product.

FDA, with the assistance of other Federal Agencies, will provide technical assistance to small processors, either directly or through the ISSC, to facilitate their adoption of available post-harvest processing technologies. Further, as it has in the past, FDA will dedicate research resources to promising new technologies in an effort to further reduce costs to the industry.

What role will ISSC and the States play in the future?

FDA intends to continue to seek the advice and support of the ISSC in the control of Vv. It is FDA’s hope that the deliberations at the 2009 ISSC biennial meeting, which begins on 10/17/09, can focus on ISSC strategies for the mandatory implementation, within the ISSC framework, of PHP for the control of this pathogen when the hazard is reasonably likely to occur.