Presence of water drastically enhanced HHP inactivation of MNV-1 on green onions. Lowering initial sample temperature significantly enhanced HHP inactivation of MNV-1. HHP inactivation curves showed a linear relationship between log reduction of MNV-1 and time. HHP could inactivate > 3.0 log of HuNoV GII.4 on green onions (in the presence of water) and in salsa.