Serum specimens were sent to the Centers for Disease Control and Prevention, where they were tested for anti-HCV by using Ortho HCV enzyme-linked immunosorbent assay (ELISA), version 3.0 (Ortho-Clinical Diagnostics, Raritan, New Jersey). Supplemental recombinant immunoblot assays (RIBA) (Chiron RIBA HCV Strip Immunoblot Assay, version 3.0, Chiron Corp., Emeryville, California) were performed on all specimens that were repeatedly reactive by ELISA testing. For those specimens classified as positive or indeterminate by RIBA, separate, archived aliquots stored at −70 °C and suitable for nucleic acid amplification testing were submitted for quantitative HCV RNA testing using Cobas Amplicor HCV Monitor Test, version 2.0 (Roche Molecular Diagnostics, Pleasanton, California). If that result was below the level of detection, a qualitative assay (Amplicor HCV Test, version 2.0, Roche Molecular Diagnostics) was performed. Samples found to be reactive by enzyme immunoassay and confirmed by RIBA or Amplicor were considered to be anti-HCV–positive. Alanine aminotransferase (ALT) levels (reference range, 0 to 39 U/L) were measured in specimens that had been stored and shipped under appropriate refrigeration conditions (4 °C to 8 °C).