- Diagnosis of Helicobacter pylori infection with a new non-invasive antigen-based assay. HpSA European study group. Vaira, D., Malfertheiner, P., Mégraud, F., Axon, A.T., Deltenre, M., Hirschl, A.M., Gasbarrini, G., O'Morain, C., Garcia, J.M., Quina, M., Tytgat, G.N. Lancet (1999)