Oyster Related Health Risks: Paralytic Shellfish Poisoning and Vibrio parahæmolyticus

Paralytic shellfish poisoning (PSP) is caused by consumption of shellfish (raw or cooked oysters, clams, mussels), or broth from cooked shellfish, that contain marine toxins elaborated by the plankton upon which the shellfish feed. Currently, all King County beaches, and several other beaches in the Puget Sound Region, are experiencing dangerously high levels of marine biotoxins that cause paralytic shellfish poisoning.

• Symptoms of PSP typically develop rapidly, within 2 hours, but as long as 18 hours after ingestion of contaminated shellfish or broth, and are predominantly neurological. They include tingling, burning, or numbness of the face and extremities, and sometimes drowsiness, incoherent speech, and a sense of “floating.” In severe cases, muscle paralysis and respiratory failure can occur, sometimes leading to death in 2 to 25 hours. Children may be more sensitive to the toxin, which is 1,000 times more potent than cyanide.
  
  
• PSP diagnosis is clinical. Laboratory confirmation can be obtained by mouse bioassay of suspect food. Other diagnoses to consider include organophosphate pesticide exposure, botulism, and ciguatera fish poisoning.
  
  
• Treatment is supportive with close monitoring of respiratory status for severe cases; anticholinesterase agents are not recommended.
  
  
• Paralytic shellfish poisoning, though not listed separately as a notifiable condition in Washington State, is considered a “Rare Disease of Public Health Importance”, and should be reported immediately to Public Health at: (206) 296-4774.

Vibrio parahæmolyticus

V. parahæmolyticus infections continue to be reported in King County, though not at the levels seen in July and August when 35 confirmed and 14 suspected cases were reported. Consumption of raw oysters continues to be the primary risk factor for infection.

• Gastrointestinal symptoms typically occur within 24 hours of ingestion, and usually resolve without treatment within 3 days. Rarely, the organism can infect open wounds exposed to contaminated water.
  
  
• Please continue to ask patients presenting with watery diarrhea, abdominal cramps, nausea, vomiting, fever and headache about recent consumption of raw or undercooked seafood, especially oysters. Obtain stool specimens from suspect cases and request culture for V. parahæmolyticus on the microbiology lab request so that the lab can use the appropriate culture media.
  
  
• Cases of confirmed V. parahaemolyticus should be reported to Public Health during regular work hours at (206) 296-4774, or on our 24 hour automated disease report line (for non-urgent reports only) at (206) 296-4782.