Temperature-dependent Survival of Hepatitis A Virus in Contaminated Green Onions

Introduction: Pre- or post-harvest hepatitis A virus (HAV)-contaminated green onions have been linked to large numbers of foodborne illnesses. Understanding HAV survival on fresh onions after contamination would assist in projecting the risk of the disease associated with consumption.

Purpose: This study defined HAV inactivation rates in green onions stored at 3 °C, 10 °C, 14 °C, and 23 °C.

Methods: Each fresh whole onion was inoculated with 20 µl of HAV, air-dried for 20 min, packed, and stored in a designated temperature between 3 and 23 °C. At each sampling, HAV was eluted by 90 sec-pulsifying in 1% beef extract containing 100 mM Tris, and 50 mM glycine, pH 8. Infectious HAV levels in eluates were determined by performing a plaque assay on confluent FRhK-4 cells. A total of 3-7 onion samples were examined at each sampling.

Results: Increase in storage temperature resulted in greater inactivation rates of HAV on onions. A reduction of 0.034 log per day was found at 3.1 ± 1.8 °C versus that of 0.185 log per day at 23.4 ± 0.7 °C. Regression correlation coefficients between the log reduction of HAV and storage temperature ranged from 0.80 to 0.98 for 8 trials. The decimal reduction times (in day) of HAV on contaminated onions were D_3.4°C = 30, D_10.3°C = 14.4, D_14.2°C = 11.4, D_20.2°C = 6.6, and D_23.4°C = 5.4. Overall a temperature increase by one degree Celsius would increase inactivation of HAV by 0.007 log per day (r²=0.97).

Significance: These data may be useful in analyzing and predicting the risks associated with HAV-contamination in green onions.