Allele-specific Conventional Reverse-transcription Polymerase Chain Reaction As a Screening Assay for Discriminating Influenza a H1N1 (H275Y) Oseltamivir-resistant and Wild-type Viruses

In early 2008, a sudden increase in oseltamivir (Tamiflu)-resistant influenza A H1N1 viruses was reported from several European countries. This resistant virus has spread globally and accounted for more than 95% of H1N1 viruses isolated in the following influenza season. A continuous close monitoring on the prevalence of this resistant virus is necessary to rationalize the choice of antiviral agents. The resistance of this novel strain to oseltamivir is conferred by an amino acid substitution from histidine to tyrosine at position 275 (H275Y) of the neuraminidase protein. This study developed and evaluated allele-specific conventional reverse-transcription polymerase chain reaction (cRT-PCR) assays to provide a simple, rapid, and low-cost option for discriminating oseltamivir-resistant influenza A H1N1 (H275Y) mutant from wild-type viruses. The evaluation was based on 90 nasopharyngeal aspirate specimens collected before, during the initial phase and at the peak of emergence of resistance. Thirty-six (40%) of these specimens were H275Y mutant, whereas the other 54 (60%) were wild-type viruses as confirmed by sequencing of the neuraminidase gene. When applied directly on the 90 nasopharyngeal aspirate specimens, the allele-specific cRT-PCR assays achieved an unequivocal discrimination for 82 (91%) specimens. Further improvement in performance is expected when applied to cell culture isolates with a higher viral titer. These allele-specific cRT-PCR assays can be a simple, low-cost option for large-scale screening of influenza isolates.