Food-borne Illness From Raw Shellfish

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:

The FDA has neither approved, nor rejected, the ICP. The FDA, while commending the ISSC for adopting the ICP, has expressed some concerns regarding the it, including the following:
  These concerns must be addressed by shellfish control authorities to adequately protect the health of consumers of raw shellfish.