SEATTLE – More than twice as many King County residents have become ill after eating shellfish this summer compared to past years.
King County health officials report there were 13 suspected cases of the saltwater bacteria vibrio parahaemolyticus in the county during July, compared to an average of four reported in that month in recent years. Since the beginning of August, an additional eight cases have been confirmed, while King County would typically only see six for the entire month.
Across Washington state, more than 40 residents have gotten sick with vibriosis.
"This is probably the tip of the iceberg,” said Dr. Jeff Duchin, chief of communicable disease for Seattle & King County Public Health. “For every case that is reported, an estimated 142 additional cases go unreported."
People typically get vibriosis from eating raw or undercooked shellfish, particularly oysters. Residents who have pre-existing medical conditions or who take antacids regularly are at higher risk for illness from the vibrio infection.
Symptoms of vibrio infection can include moderate to severe diarrhea, abdominal cramps, nausea, vomiting, fever, chills and headache. Vibrio bacteria also can cause a skin infection if open wounds are exposed to warm seawater.
To prevent vibrio infections, health officials recommend consumers thoroughly cook shellfish before eating them; never rinse cooked shellfish in seawater, which can re-contaminate them; keep raw or cooked shellfish well-refrigerated before serving; and avoid swimming in warm seawater if you have open wounds.
Officials have recommended shellfish not be harvested from areas closed due to high vibrio levels, including Hammersley Inlet and several parts of Hood Canal. Oakland Bay and Totten Inlet growing areas are also closed due to recent illnesses.
Health officials advised cooking shellfish until the shells just open is not enough to kill vibrio bacteria. Shellfish should be cooked to an internal temperature of 145 degrees for at least 15 seconds.
"We have warnings on menus about the risks of eating raw shellfish, but people might not always get the message or know that the risks are much higher this time of year," Duchin said.
Kevin Davis, owner of Blueacre Seafood, knows that consuming raw oysters could lead to infection, but that doesn’t stop him from eating one of his favorite foods.
“While the risks involved with eating raw oysters are obviously greater during the warmer months, the temptation to enjoy a few freshly shucked, ice cold oysters on the half shell on a warm summer's afternoon far outweigh the risks for many people,” Davis said.
For consumers who aren’t willing to assume that risk, Davis recommends broiling, grilling or frying oysters, which he said gets them even hotter than 145 degrees.
Davis also recommended buying oysters from a reputable source that keeps them in a cold environment and sells them fresh.
“You want as clear a chain direct from the growers as possible,” Davis said.
The Washington State Department of Health has been sending notices to shellfish growers recommending extra precautions during periods of low midday tides and warm weather, and weekly lab test results showing the levels of vibrio bacteria in growing areas.
Vibrio bacteria occur naturally in marine waters, and they grow more rapidly during the warm months. Health officials reported the early warm streak in July could have led to a longer period of vibrio presence in local waters. Once water temperatures begin to cool in October, the bacteria typically decline.
Davis said that while oysters are most popular during the summer, they actually are most abundant and at their best quality during the winter and early spring, when they are safer to eat.
“From September till May their whole existence is to feed, so all they’re doing is getting better.”
The worst outbreak of vibriosis in recent years came in 2006, when Washington had 80 lab-confirmed vibrio cases and King County had 36 confirmed cases. In 2012, King County had 26 cases of vibriosis for the entire year; so far this year, 22 confirmed or probable cases have already been reported.