Table 2.

Summary of Public Health England influenza antiviral resistance testing

Assay type	Mutation(s) detected	When this particular test is used	Considerations with the test
H275Y SNP detection assay	H275Y	Influenza A H1N1pdm09 and treated with oseltamivir	Rapid test
Resistance SNP detection assays	Most common influenza A and B mutations	Influenza A H3N2 or influenza B (regardless of which drug used)	Typically considered for patients with: (i) unsatisfactory clinical response to 10 days of treatment + non-viral causes unlikely + influenza virus remains detectable at a significant Ct value (ii) any patient who has been on neuraminidase therapy for a prolonged period i.e. greater than 1 month
Full-length neuraminidase sequencing	Uses WGS to screen for all previously reported resistance mutations	Influenza A H1N1pdm09 and treated with zanamivir primarily but may also be used for confirmation of susceptibility in influenza A H3N2 and B	May take up to 2 weeks
Phenotypic testing	Not applicable	For all influenza A and B subtypes in specific cases where deemed appropriate	Requires the use of cell grown virus isolates therefore takes a longer period of time No pre-defined ‘breakpoint’/IC50 cutoff points for drug susceptibility exist

SNP Single nucleotide polymorphism, WGS whole genome sequencing, and IC₅₀ 50% of the maximal inhibitory concentration