Predicting Susceptibility to Norovirus GII.4 by Use of a Challenge Model Involving Humans

Background. GII.4 is the predominant norovirus genotype worldwide. Challenge models involving humans have shown the association of human histo-blood group antigens (HBGAs) and susceptibility to infection with Norwalk virus (GI.1 norovirus), but the association of HBGAs and infection with other noroviruses is based on results of epidemiological studies. We performed the first GII.4 challenge study involving humans and prospectively evaluated the relationship between HBGAs and norovirus infection and associated illness. Methods. Forty healthy adults (23 secretors and 17 nonsecretors of HBGAs) were challenged with 5 x 104 reverse-transcription polymerase chain reaction (RT-PCR) units of GII.4 norovirus. Subjects were assessed daily for clinical illness, and stool specimens were evaluated for norovirus by RT-PCR. Infection was defined by detection of norovirus and/or seroconversion to GII.4 antibody. Results. Of the 23 secretors, 16 (70%) were infected with norovirus, 13 (57%) became ill (characterized by vomiting and/or diarrhea), and 12 (52%) developed norovirus-associated illness. In contrast, only 1 nonsecretor (5.9%) became ill, and another nonsecretor shed virus for a single day (P < .001 for each variable, compared with secretors). Infection occurred in secretors regardless of ABO blood group. Illness was mild to moderate in severity and lasted 1-3 days. Conclusions. Secretor status determined the susceptibility to norovirus GII.4 challenge. This human challenge model should be useful for evaluating norovirus vaccines and antiviral agents.