King
County
and other areas in
Washington
are experiencing a large outbreak of Vibrio parahæmolyticus infections associated with oyster consumption. Through July 27th, 27 confirmed cases have been reported in
King
County
in 2006, 26 of these reported in July. From 1996 to 2005, 10.6 vibriosis cases, on average, were reported each year (range 4 to 27). Typically, a mean of 2 cases, are reported in July and 4.8 in August (range 1 to 14).
Exercising caution, some restaurants have voluntarily taken raw oysters off of their menus.
Vibriosis is the term used to describe illness caused by infection with V. parahæmolyticus and other non cholera-causing Vibrio species (including non-toxigenic Vibrio cholera). The illness is usually a moderately severe enteritis lasting 1-7 days and characterized by watery diarrhea, abdominal cramps, fever, nausea, vomiting, and headache. Up to 25 percent of cases may develop a dysentery-like syndrome with high fever, bloody or mucoid stools, and elevated WBC. The incubation period is typically 12-24 hours after exposure (range, 4-30 hours). Bacteremia is uncommon, occurring mostly in persons who are immune deficient. Wound infections can occur when broken skin is exposed to warm sea water.
Clinicians should consider V. parahæmolyticus in patients with a compatible clinical syndrome and take a travel and food history including history of eating raw or undercooked seafood, particularly shellfish. If possible, obtain details related to suspected shellfish consumption, including the location and dates of meals. As with other enteric infections of public health significance (i.e., E. coli 0157:H7, shigella, salmonella) it is important that clinicians obtain stool cultures to confirm the etiology of infection. Culture results are important for public health investigations and resulting measures to interrupt transmission. Please specify on the microbiology lab request that V. parahæmolyticus culture is being requested so that the lab can use the proper selective culture media for vibrios (Typically Thiosulfate Citrate Bile Sucrose Agar or TCBS agar).
V. parahæmolyticus lives worldwide in marine coastal environments. In warm weather, increasing numbers of the organisms multiply in the gut of filter feeding mollusks such as oysters, clams, and mussels. Oysters, commonly eaten raw, are the most common food associated with vibrio infection in the
United States
. V. parahæmolyticus is killed by cooking to 145ºF.
V. parahæmolyticus infection is not considered particularly communicable, though fecal-oral transmission is theoretically possible. Persons especially susceptible to infection are those with chronic liver disease, decreased gastric acidity, diabetes, peptic ulcer, or immunosuppression. Of the 25 cases reported so far in July 2006, approximately 1/3 reported taking prescription or over-the-counter antacids, H2 blockers, or proton pump inhibitors.
The Washington Food Safety and Shellfish program monitors commercial and recreational shellfish harvest sites for V. parahæmolyticus. Sites where high levels are found are closed for shellfish harvesting. In addition, restaurants and other retail outlets are required to keep shellfish tags identifying the harvest site for every oyster, clam, and mussel they sell. When a confirmed or suspect case of vibriosis is reported, the case is rapidly interviewed by Public Health, and tags from implicated shellfish are retrieved used to identify implicated product and/or growing areas. Since July, multiple growing areas and beaches have been closed for shellfish harvesting in response to the increase in vibrio cases.
Cases of confirmed V. parahæmolyticus should be reported to Public Health during regular work hours at 206-296-4774 or on our 24 hour automated disease report line at 206-296-4782.
