Tiling probes spanning the entire genome segments on both the forward and reverse strands were created at one base resolution (8) . Analysis of the sequence alignments revealed that there were no deletions, insertions or recombination. However, we found 36 mutation hotspots in the alignments where mutations occurred near one another (within 20 bp). Thus, we added additional probes that represent all possible combinations of mutations in these mutation hotspots onto the array. To ensure that we have accurate sequence of the drug binding pocket targeted by NA inhibitors (13) 