Vibrio: Minus Tides and Warm Temperatures Increase Risks of Contracting Vibriosis from Washington Oysters

 

Department of Health Issues Notice to Growers

Warning of the Vibrio Season

Minus Tides and Unseasonably Warm Temperatures

Increase the Risk

 

Relative increase of Vibriosis (top line)

Center for Disease Control

 

DOH reminds shellfish growers of consumers contracting vibriosis from shellfish

In response to the continuing increase in vibriosis contracted from consumption of raw oysters harvested from Puget Sound, Washington's Department of Health (DOH) has reminded shellfish growers about the Vibrio parahaemolyticus (Vp) control plan taking effect May 1. Puget Sound growers are required to follow strict guidelines on time allowed to cool shellfish to 50 degrees after harvest. Times range from 12 hours in May to 4 hours in July and August. Despite similar plans existing in all states vibriosis from oysters harvested in the United States continues to increase.

 

Growing areas in south Puget Sound

closed in 2013 from vibriosis

 

 

Virulent Pacific Northwest strain now found on the East Coast

The sharpest rise of vibriosis occurred on the East Coast where what is described as the "Pacific Northwest" strain of Vibrio parahaemolyticus (Vp) is felt to have become endemic, as it is in Puget Sound. Vibriosis from this strain of Vp was not found in shellfish outside of the northwest where Vp occurs naturally. Then, in 2012, outbreaks traced to shellfish from large areas of the East Coast occurred. Vibriosis from this virulent northwest strain of Vp traced to shellfish from the East Coast continues to climb, as it has been from shellfish harvested in Puget Sound  (see the Center for Disease Control article here).

 

Extra precaution: Average temperatures and average tides don't always fit the formula

Not mentioned by DOH is the first few days of May, 2014, bring with it minus mid-day tides and unseasonably warm weather, peaking at 85 degrees on May 1. As seen in the table below, normal temperatures for the first week in May average in the mid-sixties. The upcoming forecast notes day time temperatures climbing into the mid-80's on Thursday, May 1, when at 2PM the tide in south Puget Sound will reach its low of -1.6 (see "May 2014 Tide Table" below). This will leave oysters exposed to the unseasonably warm temperature for over four hours.

 

Average Temperatures: ~65 degrees

 

Forecast Highs for Shelton:

April 30, 81 degrees; May 1, 85 degrees

 

May 2014 Tide Table

(Olympia)

 

Time for post harvest processing?

The shellfish industry has for years been trying to control the outbreaks of vibriosis traced to shellfish harvested during the warm summer months. A few years ago the FDA proposed shellfish be processed immediately after harvesting (e.g., cold shock, hydrostatic high-pressure, irradiation). An intense lobbying effort by the shellfish industry pushed back the effort leaving it up to the industry to handle, as they have been for years. During that time vibriosis from the consumption of raw oysters has continued to climb. (read article on PHP here)