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A New Season, a New Plan:
Preventing Oyster-Associated Vibriosis
June 2007                                                                                                          Vol. 12, No. 6

During the summer of 2006, health districts reported an unprecedented increase in gastroenteritis cases associated with the consumption of raw oysters.  From May through August last year, 267 confirmed and probable reports of vibriosis attributed to Washington grown oysters, were reported from Washington and six other states or provinces.

Vibrio occur naturally in coastal waters, particularly with warmer water temperatures.  Vibrio parahaemolyticus, one of several Vibrio species pathogenic to humans, is the most common cause of shellfish-associated illness in Washington.

Although frequently present in oysters and other bivalve mollusks, V. parahaemolyticus generally does not reach levels high enough to cause illness.  However, there can be rapid growth of V. parahaemolyticus to levels that result in infection if the harvested seafood is not kept at refrigerator temperatures (<5^oC or 40^oF).  V. parahaemolyticus infection causes profuse watery diarrhea, vomiting, and fever. The incubation period is eight to 72 hours. Symptoms may last several days to a week and the diarrhea can be severe.  Rarely the resulting dehydration can be life threatening.

As we enter the warmer summer months, it is important to re-emphasize that control of illness due to V. parahaemolyticus includes actions on the part of public health agencies, health care providers, shellfish suppliers, and consumers.

New Vibrio Control Plan

In response to the outbreak of 2006, DOH established a new State Vibrio Control Plan <http://www.doh.wa.gov/ehp/sf/VpEmergencyRule246-282-006.doc > addressing shellfish safety.  DOH Office of  Shellfish and Water Protection, Food Safety Program, Communicable Disease Epidemiology, and Public Health Laboratories collaborated with external partners including the commercial shellfish industry, Centers for Disease Control and Prevention, the Food and Drug Administration, Tribes, and other states and Canada to develop the plan.

The plan is designed to implement stricter requirements relating to the harvest and shipment of oysters intended for raw consumption during the months of June through September.  Features of the plan include reduction in time to get shellfish under refrigeration after harvesting, increase in number of shellfish growing areas regularly monitored for Vibrio levels, and new sampling strategies designed to test product exposed to highest ambient temperatures.

Commercial companies operating in 24 specific shellfish growing areas will participate in the control plan during 2007.  This includes using standardized handling procedures for harvesting oysters to prevent elevated temperatures. The accuracy of information provided on licensed shellfish tags has been reviewed by DOH and companies will receive technical assistance to bring them into compliance with tagging requirements.

During 2006 the actions needed to interrupt the V. parahaemolyticus (VP) outbreak rested firmly on public health surveillance for human illness, as existing shellfish monitoring strategies did not detect an increased risk in time to prevent the outbreak.

 
Washington State Department of Health -- Communicable Disease Epidemiology Section

Local health jurisdictions (LHJs) continue to play a key role in limiting the impact of shellfish associated illness. Actions available to LHJs include encouraging health care providers and local laboratories to report cases, promptly initiating traceback investigations, assessing shellfish handling conditions at the retail level, and immediately reporting cases and shellfish source information to DOH. The investigation and immediate reporting of all suspected shellfish-associated illness including foodborne illness complaints, single case reports, as well as outbreaks, is needed for early identification of source contamination and to prevent additional illnesses.

Vibrosis is notifiable to local health jurisdictions.  Health care providers and health care facilities should report suspect and confirmed cases to the appropriate local health jurisdiction <http://www.doh.wa.gov/LHJMap/LHJMap.htm>.  Laboratories, while not required by law to report isolation of Vibrio species to public health agencies, make a valuable contribution when reporting voluntarily, particularly in health care systems where providers rely on laboratory reporting.

Recreational consumption of raw oyster
 "shooter."   Credit: Laura Slaybaugh

The local health jurisdiction conducts an interview to determine the specific products consumed by the case patient.  Public health agencies contact commercial sources of implicated shellfish in order to identify the harvest site.  Restaurants and markets provide tags from their shellfish which allow the trace back linking the purchases to the specific beds where the implicated product was harvested. Timely illness reports are a crucial element in the ability to implement appropriate harvest restrictions.

Recommendations

Lastly, before enjoying the fruits of our rich Puget Sound tidelands, recreational shellfish harvesters and consumers should heed the following recommendations:

• Always check the health status of the harvest beach at DOH’s Recreational Beach Maps
  <http://www.doh.wa.gov/ehp/sf/>

• Harvest as soon as possible after the tide goes out (at the beginning of the tide cycle instead of at the end

• Do not harvest oysters that have been exposed to direct sunlight for more than one hour

• Place oysters under refrigeration or on ice as soon as possible

• Cooking will destroy Vibrio. To reduce the risk of illness, thoroughly cook shellfish (heat oysters to 145^oF) and avoid contamination of food with raw shellfish or their juices

• Immuno-compromised persons should never consume raw shellfish

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New "Rabies Specimen Packaging Procedure" Quick Reference Sheet

During the warmer months, the Public Health Laboratories receive an increased number of calls regarding correct packaging and shipping of specimens for rabies testing.  A quick reference page  <http://www.doh.wa.gov/Notify/other/rabiesspec.pdf> for packaging and shipping rabies specimens has been developed for the convenience of local health jurisdiction personnel who answer questions regarding collection, packaging, and shipping of specimens for rabies testing. 

For complete written guidelines on rabies specimen collection, go to: http://www.doh.wa.gov/notify/other/rabiesspecimenguidelines_Aug06.pdf

Documents posted in .pdf version on the Department of Health Web site will be made available in an alternative format on request to users who are unable to download or view .pdf files on the Web. To request an alternative format, contact: Webmaster.

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