Rapid quantification of single-nucleotide mutations in mixed influenza A viral populations using allele-specific mixture analysis

Monitoring antiviral resistance in influenza is critical to public health epidemiology and pandemic preparedness activities. Effective monitoring requires methods to detect low-level resistance and to monitor the change in resistance as a function of time and drug treatment. Resistance-conferring single-nucleotide mutations in influenza virus are ideal targets for such methods. In the present study, fives sets of paired TaqMan^® allele-specific PCR (ASPCR) assays were developed and validated for quantitative single-nucleotide polymorphism (SNP) analysis. This novel method using ΔCt is termed allele-specific mixture analysis (ASMA) or FluASMA. The FluASMA assays target L26F, V27A, A30T, and S31N mutations in the A/Albany/1/98 (H3N2) M2 gene and H275Y mutation in the A/New Caledonia/20/99 (H1N1) NA gene and have a limit of quantification of 0.25-0.50% mutant. The error for % mutant estimation was less than 10% in all FluASMA assays, with intra-run ΔCt coefficient of variance (CoV) at ≤2% and inter-run ΔCt CoV at ≤5%. Results from the current study demonstrate that FluASMA is a highly sensitive and quantitative SNP analysis method, even for minor mutant components (<1%).