If all human DNA cannot be removed from the sample, simulations indicate that on average, multiplexes of 10-mer primers are expected to produce hundreds of amplicons from the human genome, which would appear as a smear on a gel ( Figure 4 ). With primers of length 11-14, there is a large variation among bins. While most short sequences do occur in the human genome (33) , an amplicon requires that two occur in proximity, and primers !11 bases make this a sporadic event for bins with only 10 primers. Nonetheless, imperfect sample purification to eliminate eukaryotic nucleic acids could be problematic for universal viral priming using primers shorter than 15 bases, particularly for multiplexes of 10 or more primers.