Authorities in Oregon have closed the entire state's coastline after an “unprecedented” outbreak of shellfish poisoning led to 20 people being struck down.
The illnesses were caused by saxitoxin, a naturally occurring toxin produced by algae, and has led the US state’s governance to close off sections of beach for mussel harvesting.
Oregon's Department of Fish and Wildlife and Department of Agriculture announced the new closures on Thursday.
Department shellfish programme manager Matthew Hunter said: “We've had a paralytic shellfish poisoning event in Oregon that we have never seen in the state.
“The outbreak's unprecedented nature was due both to the number of species impacted and the number of people falling ill.”
He added that elevated levels of toxins were first detected in shellfish on the state's central and north coasts on May 17.
Oregon Health Authority said people who eat shellfish contaminated with high levels of saxitoxins usually start feeling ill within 30 to 60 minutes.
Symptoms include numbness of the mouth and lips, vomiting, diarrhoea, and shortness of breath and irregular heartbeat in severe cases.
There is no antidote, according to the agency, and treatment for severe cases may require mechanical ventilators to help with breathing.
State health officials are asking people who have harvested or eaten Oregon shellfish since May 13 to fill out a survey.
The paperwork will help investigators identify the cause of the outbreak and the number of people sickened.
Officials in neighbouring Washington have also closed the state's Pacific coastline to the harvesting of shellfish, including mussels, clams, scallops and oysters, a shellfish safety map produced by the Washington State Department of Health showed.
