Table 2. Results from neuraminidase inhibition (NAI) and iART assays for virus isolates carrying NA amino acid mutations conferring various degrees of oseltamivir resistance (n = 42) or no such mutations (controls; n= 4).
| Virus | NA mutations | NAI assay | iART | ||||
|---|---|---|---|---|---|---|---|
| Straight numbering | N2 numbering | IC50, nM Mean ± SDa |
Fold | Interpretationb | R-factor, Mean ± SD | Resultc | |
| A(H1N1)pdm09 | |||||||
| A/Washington/29/2009 | H275Y | H274Y | 208.76 ± 27.05 | 1,228 | HRI | 4.1 ± 0.12 | Resistant |
| A/North Carolina/39/2009 | H275Y | H274Y | 199.43 ± 4.38 | 1,173 | HRI | 5.17 ± 0.12 | Resistant |
| A/India/1027/2013 | H275Y | H274Y | 185.44 ± 15.95 | 1,091 | HRI | 5.30 ± 0.38 | Resistant |
| A/Delaware/08/2011 | H275Y | H274Y | 174.53 ± 21.24 | 1,027 | HRI | 4.16 ± 0.73 | Resistant |
| A/Hawaii/67/2014 | H275Y | H274Y | 171.48 ± 31.01 | 1,009 | HRI | 4.21 ± 0.58 | Resistant |
| A/Michigan/65/2015 | H275Y | H274Y | 158.76 ± 28.68 | 934 | HRI | 5.77 ± 0.22 | Resistant |
| A/Denmark/528/2009 | H275Y | H274Y | 153.26 ± 14.47 | 902 | HRI | 5.30 ± 0.26 | Resistant |
| A/Georgia/31/2016 | H275Y | H274Y | 150.48 ± 24.48 | 885 | HRI | 5.60 ± 0.19 | Resistant |
| A/Maryland/04/2011 | H275Y | H274Y | 145.64 ± 4.41 | 857 | HRI | 5.30 ± 0.53 | Resistant |
| A/Washington/31/2016 | H275Y | H274Y | 141.00 ± 9.58 | 829 | HRI | 5.76 ± 0.60 | Resistant |
| A/Texas/23/2012 | H275Y | H274Y | 145.07 ± 30.07 | 805 | HRI | 5.48 ± 0.67 | Resistant |
| A/Colorado/30/2015 | H275Y | H274Y | 132.40 ± 32.65 | 779 | HRI | 5.84 ± 0.30 | Resistant |
| A/Texas/48/2009 | H275Y | H274Y | 120.22 ± 18.65 | 707 | HRI | 3.85 ± 0.19 | Resistant |
| A/Bolivia/1278/2014 | I223R | I222R | 11.68 ± 0.15 | 65 | RI | 1.99 ± 0.30 | Resistant |
| A/Tennessee/24/2016 | S247R | S246R | 6.61 ± 0.45 | 37 | RI | 5.67 ± 0.47 | Resistant |
| A/India/1819/2016 | S247R | S246R | 6.31 ± 0.09 | 35 | RI | 7.58 ± 0.47 | Resistant |
| A/Dnipro/133/2014 | S247R | S246R | 5.66 ± 0.10 | 31 | RI | 3.79 ± 0.35 | Resistant |
| A/Chile/1579/2009 | I223K | I222K | 2.84 ± 0.65 | 16 | RI | 0.42 ± 0.03 | Nonresistant |
| A/Pennsylvania/05/2016 | D199G | D198G | 1.47 ± 0.03 | 8 | NI | 1.03 ± 0.26 | Resistant |
| A/California/12/2012 | Controld | 0.18 ± 0.06 | 1 | NI | 0.24 ± 0.16 | Nonresistant | |
| A(H3N2) | |||||||
| A/Bethesda/956/2006 | R292K | R292K | > 1,000 | > 14,285 | HRI | 7.22 ± 0.24 | Resistant |
| A/Texas/12/2007 | E119V | E119V | 37.92 ± 5.56 | 542 | HRI | 1.06 ± 0.11 | Resistant |
| A/Massachusetts/07/2013 | E119V | E119V | 37.33 ± 10.40 | 533 | HRI | 1.04 ± 0.04 | Resistant |
| A/Arkansas/13/2013 | E119V | E119V | 34.88 ± 2.69 | 498 | HRI | 1.22 ± 0.11 | Resistant |
| A/Illinois/03/2015 | E119V | E119V | 31.98 ± 3.70 | 458 | HRI | 1.32 ± 0.14 | Resistant |
| A/Washington/33/2014 | E119V | E119V | 29.83 ± 6.56 | 426 | HRI | 1.19 ± 0.08 | Resistant |
| A/Massachusetts/07/2013 | Del245–248 | Del245–248 | 21.70 ± 3.59 | 310 | HRI | 1.74 ± 0.06 | Resistant |
| A/Washington/01/2007 | Control | 0.07 ± 0.02 | 1 | NI | 0.16 ± 0.07 | Nonresistant | |
| B/Victoria lineage | |||||||
| B/Florida/103/2016 | A200T | A201T | 318.19 ± 37.76 | 23 | RI | 7.30 ± 0.09 | Resistant |
| B/Bangladesh/3008/2013 | E117G | E119G | 115.54 ± 10.19 | 8 | RI | 4.34 ± 0.45 | Resistant |
| B/Laos/1471/2016 | N294S | N294S | 108.37 ± 12.31 | 8 | RI | 2.29 ± 0.55 | Resistant |
| B/Mexico/4260/2016 | I221V | I222V | 58.57 ± 9.38 | 4 | NI | 2.42 ± 0.03 | Resistant |
| B/Laos/0425/2016 | Control | 13.99 ± 0.61 | 1 | NI | 0.95 ± 0.18 | Nonresistant | |
| B/Yamagata lineage | |||||||
| B/Illinois/03/2008 | E117A | E119A | > 1,000 | > 112 | HRI | 10.44 ± 0.26 | Resistant |
| B/Hong Kong/36/2005 | R374K | R371K | > 1,000 | > 112 | HRI | 9.11 ± 0.28 | Resistant |
| B/Memphis/20/1996 | R150K | R152K | 591.47 ± 61.79 | 66 | HRI | 3.99 ± 0.36 | Resistant |
| B/Vermont/15/2015 | D197N | D198N | 73.76 ± 8.17 | 8 | RI | 2.39 ± 0.18 | Resistant |
| B/Santiago/75552/2015 | D197N | D198N | 54.81 ± 6.48 | 6 | RI | 2.59 ± 0.24 | Resistant |
| B/Gorbea/75877/2015 | D197N | D198N | 49.51 ± 8.85 | 6 | RI | 2.49 ± 0.03 | Resistant |
| B/Ontario/1110/2011 | H273Y | H274Y | 57.48 ± 6.98 | 6 | RI | 1.66 ± 0.16 | Nonresistant |
| B/California/88/2015 | H273Y | H274Y | 50.18 ± 7.58 | 6 | RI | 1.78 ± 0.34 | Nonresistant |
| B/Florida/05/2016 | K152N | K154N | 43.59 ± 4.88 | 5 | RI | 4.09 ± 0.29 | Resistant |
| B/Utah/15/2016 | D197N | D198N | 38.72 ± 3.19 | 4 | NI | 3.06 ± 0.58 | Resistant |
| B/Rochester/02/2001 | D197N | D198N | 37.08 ± 1.96 | 4 | NI | 2.40 ± 0.33 | Resistante |
| B/Wisconsin/42/2016 | G407S | G402S | 36.08 ± 3.52 | 4 | NI | 1.99 ± 0.10 | Nonresistant |
| B/Rochester/02/2001 | Control | 8.93 ± 0.82 | 1 | NI | 0.97 ± 0.12 | Nonresistant | |
Del: deletion; iART: influenza Antiviral Resistance Test; IC50: inhibitory concentration 50%; R-factor: ratio of chemiluminescent signal intensity generated by viral neuraminidase activity on the substrate, with and without inhibitor (i.e. oseltamivir carboxylate); SD: standard deviation.
a Mean and standard deviation based on the results from at least three independent experiments.
b Criteria for reporting NAI assay results based on an IC50 fold increase compared with the reference IC50 value (control virus): for influenza A, normal (< 10-fold), reduced (10–100-fold) and highly reduced (> 100-fold) inhibition, and for influenza B the same criteria, but using < 5-fold, 5–50-fold and > 50-fold increases [9]; NI, normal inhibition; RI, reduced inhibition; HRI, highly reduced inhibition.
c Output result as shown on the device’s display; result is based on the pre-set cutoffs for influenza A (≥ 0.7) and B (≥ 2.2) viruses.
d Control, a virus lacking NA changes (amino acid substitutions or deletions) associated with altered inhibition by oseltamivir, was included for each antigenic group (type/subtype/lineage) and used to determine a fold change and a degree of inhibition.
e Two results were displayed as resistant and one as nonresistant.