title: Clustering of progressive multifocal cases of leukoencephalopathy.
mesh_terms: D006801:Humans; D007968:Leukoencephalopathy, Progressive Multifocal / Q000453:epidemiology* / Q000382:microbiology; D027383:Papillomaviridae / Q000302:isolation & purification; D010507:Periodicity; D027382:Polyomaviridae; D013548:Sweden