Pre-challenge serum samples were tested for the 18 infected subjects; 12 met clinical definition of gastroenteritis (GE, triangles), 6 did not meet definition of gastroenteritis (No GE, squares). (A) BT50s, (B) total anti-NV ELISA titers. The two empty triangles in panel A represent detectable BT50s in the GE group, and their respective anti-NV titers are shown in panel B.