By Melanie R. Margolis

Now that summer has arrived, those who enjoy eating raw shellfish may think twice about ordering their next plate of oysters on-the-half-shell as they recall warnings about raw oyster consumption from summers past. The naturally occurring Vibrio parahaemolyticus bacteria has caused illnesses related to oysters harvested in New York, Texas, and Washington during the last two summers. Because New York, Texas, and Washington had the first Vibrio parahaemolyticus illnesses linked to consumption of raw oysters in the United States, the states did not have in place statutes or regulations addressing the particular problem.

It is not unusual for Vibrio parahaemolyticus to be found in raw oysters but usually it is found at levels that do not cause health problems. The bacteria naturally occur in marine coastal waters throughout the year but are more abundant in warm weather. Symptoms of illness include watery diarrhea and abdominal cramps, sometimes accompanied by nausea, vomiting, fever and headache. The incubation period varies from 4 to 30 hours with the illness usually lasting from 1 to 7 days. The illness is rarely fatal, but can be life-threatening to persons who have liver problems or weakened immune systems. Thorough cooking destroys the bacteria.

In Texas, Senate Bill 1685, which unanimously passed both houses and was sent to Governor George Bush on May 26, 1999, addresses, among other oyster-related issues, the closing and reopening of bays for harvesting of oysters in the event of the presence of higher than normal amounts of illness-causing, naturally occurring marine bacteria in oyster meat. The Texas bill provides that the Texas Department of Health (TDH) shall employ standards at least as stringent as the National Shellfish Sanitation Program NSSP guidelines and that TDH's approach must be consistent with the purpose and intent of the federal Food and Drug Administration (FDA) policy statements regarding the consumption of raw shellfish.

The FDA is responsible for federal administration of the NSSP. The NSSP is a program for state shellfish control agencies, the shellfish industry, and federal agencies that sets guidelines for the sanitary control of the shellfish industry. NSSP's Manual of Operations, published by the FDA, is a guide for establishing state shellfish laws and regulations. It is updated at the annual Interstate Shellfish Sanitation Conference (ISSC), formed in 1982 to foster and promote shellfish sanitation through the cooperation of federal and state authorities, the shellfish industry and the academic community. One of the ISSC's purposes is to adopt uniform procedures to be implemented by all shellfish control agencies. The FDA provides technical assistance to the ISSC and helps develop program criteria and guidelines.

The ISSC adopted the Interim Control Plan for Vibrio parahaemolyticus (ICP) as a guidance document. It was developed after Washington state faced a Vibrio parahaemolyticus problem in 1997. The ICP sets forth actions to be taken in the event of varying numbers of human illnesses reported and detection of varying degrees of bacteria levels, as follows:

• If waters of a state have been determined to be the source of two or more Vibrio parahaemolyticus-caused illnesses, the state shall adopt a plan for all affected shellfish growing areas. Shellfish authorities shall implement an environmental sampling plan to monitor Vibrio parahaemolyticus levels. Authorities shall notify the shellfish industry and local health jurisdictions of the potential for Vibrio parahaemolyticus-caused illnesses at least once a year and prior to times problems occurred historically.

• When more than 5 confirmed illnesses occur in a 30-day period or 3 in a 7-day period from any harvest area, or more than 1 sample with more than 100 MPN but less than 1,000 MPN Vibrio parahaemolyticus bacteria per gram of shellfish meat is detected, the authority shall collect 2 or more samples per month from each indicator station, notify the shellfish industry, recommend that shellfish stock be refrigerated under 50°F within 10 hours of harvest, and advise other relevant authorities and the industry of the potential problem.

• When more than 10 confirmed illnesses occur in a 30-day period or 6 in a 7-day period from any harvest area, or more than 1 sample with more than 1000 MPN but less than 5,000 MPN Vibrio parahaemolyticus bacteria per gram of shellfish meat is found, the authority shall collect samples weekly from each indicator station, require that shellfish stock be refrigerated under 50°F within 10 hours of harvest, notify the ISSC, other authorities and members of the shellfish industry in the state, issue a health advisory to the public about the potential problem, and encourage the industry to educate wholesalers, retailers, and consumers about the potential problems with recommendations that the product not be consumed raw.

• When more than 20 confirmed illnesses occur in a 30-day period or 10 in a 7-day period from any harvest area, or more than 1 sample with more than 5,000 MPN but less than or equal to 1,000 MPN Vibrio parahaemolyticus bacteria per gram of shellfish meat is detected, the authority shall collect samples weekly from each indicator station, ban harvesting from affected areas for raw consumption, require "cook thoroughly" labeling, and educate wholesalers, retailers, and consumers not to consume shellfish raw.

• When an outbreak is confirmed or more than one sample has more than 10,000 MPN Vibrio parahaemolyticus bacteria per gram of shellfish meat, the authority shall conduct an investigation, collect samples weekly from each indicator station, issue health advisories to the public, and prepare a written report to the FDA region. In determining whether to reopen an area to harvesting, the authority shall consider: (i) if the level of Vibrio parahaemolyticus has increased in concert with the outbreak, reopening of the affected areas could occur when the levels are reduced to baseline levels for that area; (ii) Vibrio parahaemolyticus strains of virulent genotypes are absent; and/or (iii) environmental conditions shift to those unfavorable to Vibrio parahaemolyticus growth or to those historically unrelated to Vibrio parahaemolyticus growth.

• The ICP is triggered based on: (i) numbers of reported illnesses within specified time periods and/or (ii) shellstock samples. According to the FDA, such illnesses are not timely and uniformly reported nationwide. Also, the level of pathogen per sample is arbitrary and does not relate to risk of illness. The ICP calls for 10,000 MPN of Vibrio parahaemolyticus bacteria per gram to trigger closure of a harvest area. This number has traditionally been used in regulating shellfish, but recent information indicates that the number may be too high and the presence or absence of a virulent strain of Vibrio parahaemolyticus may be more relevant than the total count.

• 20 illnesses in a 30-day period or 10 illnesses in a 7-day period from any harvest area may occur before restrictions on harvesting are triggered. The numbers of illnesses may exceed these numbers and harvesting and sale of shellfish are permitted with the addition of labeling and notification requirements to indicate that the shellfish should be cooked thoroughly. The FDA does not agree with delaying harvesting restrictions until such a high number of illnesses are confirmed, nor does it approve of shipping shellfish that is not safe for raw consumption.

• The FDA further noted that the criteria for reopening harvesting areas should be clarified because they may be misinterpreted.

05/31/99