Performance of cold chains and modeled growth of Vibrio parahaemolyticus for farmed oysters distributed in the United States and internationally

Vibrio bacteria can accumulate in molluscan shellfish and cause human diseases. The United States (U.S.) has implemented Vibrio Control Plans to mitigate risks associated with these bacteria, which include time and temperature requirements for post-harvest processing and maintaining an unbroken cold chain. In this study, we tracked the performance of cold chains for U.S. farmed oysters distributed nationally and internationally using temperature sensors. Boxes and bags of oysters (n = 125) were shipped from farms in Washington State and the Chesapeake Bay to 143 unique businesses in 20 U.S. states, Washington D.C., and Hong Kong, China. Eighty-one percent of the temperature sensors were returned with usable data. The average product temperature among all participants was 4.4 ± 2.7 °C (40 ± 5 °F), which is 5.6 °C (10 °F) cooler than the 10 °C (50 °F) guidance criterium established by the U.S. government. There were spikes in temperature in some shipments: 18% of shipments (16/91) experienced oyster temperatures above 10 °C for one hour or more, and the median time spent out of temperature control was 2.5 h. We modeled V. parahaemolyticus abundance using temperature sensor data and 75% (68/91) of shipments had a net decrease in V. parahaemolyticus abundance in the cold chain. There are opportunities for improvements in cold chain performance in the shellfish industry and related businesses. In the discussion we provide recommendations for oyster producers related to product cooling, for businesses that handle shellfish, and for government and industry groups to develop guidance for shipping by air, among other issues.