Labeling of PCR Products and Hybridization. PCR products were purified using a spin column procedure [Qiagen or Stratagene, (La Jolla, CA)]. One g of each purified PCR product was labeled with biotin-dUTP in a primer extension reaction using random hexamers and Klenow po- forward primer GAATGATGAGAAATGGACAGAAATG a Strains are identified by their GenBank accession number. b HAV sequence alignment is presented as the positive (sense) genomic strand in 5' to 3' orientation. The primer sequence and nucleotide identity is based on the genomic sequence and nucleotide numbering of HM175 strain 18f (M59808) at nucleotide positions 3399 to 3423.