| clustering of residence of multiple sclerosis patients at age 13 to 20 years in hordaland, norway. | geographic and temporal variation and migration studies point to an exogenous agent in the etiology of multiple sclerosis. if infectious etiology is involved, space-time clustering would also be expected. the authors analyzed 381 patients with a clinical onset of multiple sclerosis between 1953 and 1987 in the county of hordaland, norway. patients within the same birth cohort had lived significantly closer to each other than would be expected during ages 13-20 years, with peak clustering at age ... | 1991 | 1851394 |