Red dye tests shellfish safety

Last winter dozens of people in Washington reported vomiting, stomach pain and watery diarrhea after eating raw oysters. The highly contagious culprit: Norovirus. The outbreak prompted a large shellfish recall and closed shellfish harvesting in Mason County’s Hammersley Inlet for weeks.

Ensuring the safety of one of the nation’s largest commercial shellfish industry is no small task. Washington State Department of Health has the responsibility for making sure federal standards regarding growing and harvesting are strictly followed.

Environmental Health & Safety Director Rick Porso takes pride in the work of his shellfish program staff and the reputation of Washington’s aquiculture —oysters, mussels, clams and geoducks —that all support our state’s economy and sell for top dollar worldwide.

“Shellfish from Washington are eaten all over the world, much of it consumed raw. We take our responsibility to protect public health seriously. Even one outbreak is too many,” reflects Porso.

When the norovirus outbreak began unfolding last winter, our shellfish team began looking for the source. DOH’s epidemiologists found a match between the virus strain and the shellfish eaten. Staff then worked to trace the shellfish back to the area where the shellfish were grown and harvestedand looked at all potential pollution sources that could have the caused of the illnesses.

Our ability to follow shellfish from a dinner party at a restaurant back to the spot they were harvested, including the day and time of harvest, is a testament to how seriously we take our responsibility for shellfish safety in Washington.

While we were able to locate where the shellfish that caused the norovirus outbreak had come from, environmental evaluations of the harvest area didn’t find the cause. Regardless, the harvest area remained closed for several weeks. Once the area reopened there were no new illnesses, but that wasn’t good enough for our shellfish team.

Norovirus comes from people and it isn’t found naturally in the environment. We looked at the local sewage treatment plant and septic systems in the area. To really get answers it was agreed a dye study would be the best tool.

A dye study — where fluorescent dye is added to water then followed by scientists — takes months of planning, with an army of participants: FDA, Fish & Wildlife, Ecology, shellfish growers, Tribal representatives and the city. Specialized equipment is delivered and experts from around the country fly in to help conduct the study.

On December 1 at 4:30 a.m., a pump began injecting rhodamine — a dark, almost purple red dye safe for marine life and people — into the wastewater at the end of the treatment process, the “effluent.” While the effluent was released from the holding tank into Hammersley Inlet, three small boats prepared to monitor the dye’s progress.

Days before, six cages containing oysters were submerged at different points in the inlet and Oakland Bay. Nine devices, called fluorometers, were also placed in various underwater locations. Fluorometers continuously measure dye concentration and provide valuable data to the study team. Periodically the oysters will be retrieved and sent to a lab in Alabama to be analyzed for any viruses or bacteria that have accumulated in the shellfish.

For 24 hours the dye was continuously pumped into the effluent and released into the inlet. For days after the release, the team follows the dye’s progress.

It will take some time, but after data is collected and analyzed, the results will inform health and shellfish industry officials how to prevent future outbreaks.

Onlookers hoping to see a crimson inlet and bay were disappointed. The dye remained well beneath the surface until tide changes allowed it to mix. By that time, it was very dilute and hard to see with the naked eye. Perhaps next time…

Study goals:

• Ensure the waste treatment plant is removing viruses and bacteria. Wastewater samples will be taken throughout the treatment process to compare microbes before, during and after.
• By using the dye as a marker, learn what concentration and how rapidly effluent reaches the shellfish growing area boundary.
• Gain a better understanding of the accumulation of bacteria and viruses in shellfish at various points in the inlet.