We also identified sequences derived from single-stranded DNA viruses in some samples. In one sample we detected Parvovirus B19-derived reads with high identity to database sequences. Sequences related to various members of the Anelloviridae virus family (TTVs) were detected in 21 (17%) samples. This frequency of detection is within the range reported previously for human serum [43, 44] . The TTV sequences ranged from 40-97% amino acid identity to their closest database matches. We did not pursue these sequences further, because TTVs are known to form a divergent family of viruses and are commonly detected in apparently healthy individuals.