Table 2.

Statistical analyses of neuraminidase inhibitor susceptibility data of influenza viruses, assessed in the NA-Fluor™ NI assay

Influenza type and subtype	NAI	IC50, nm
		All isolates (including outliers)							Isolates (excluding outliers)
		No. of isolates (n)*	Min–Max**	Q1***	Median†	Q3††	IQR†††	Statistical cutoff‡	No. of isolates (n)‡‡	Min–Max‡‡‡	Mean (±SD)§	Median§§
A (H1N1) pdm09	Oseltamivir	449	0·10–294·72	0·15	0·18	0·22	0·07	0·43	437	0·10–0·41	0·19 ± 0·05	0·18
	Zanamivir	449	0·10–1·03	0·15	0·17	0·19	0·04	0·31	447	0·10–0·31	0·17 ± 0·03	0·17
A (H3N2)	Oseltamivir	978	0·03–0·76	0·10	0·11	0·13	0·03	0·22	951	0·03–0·22	0·11 ± 0·03	0·11
	Zanamivir	978	0·12–23·75	0·22	0·26	0·30	0·08	0·54	947	0·12–0·54	0·26 ± 0·07	0·25
A (H3N2)v	Oseltamivir	156	0·08–5·30	0·13	0·15	0·17	0·04	0·29	155	0·08–0·21	0·15 ± 0·03	0·15
	Zanamivir	156	0·27–35·74	0·46	0·51	0·60	0·14	1·02	155	0·27–0·74	0·52 ± 0·09	0·51
B	Oseltamivir	343	0·83–53·02	6·49	8·54	10·39	3·90	22·09	338	0·83–21·73	8·77 ± 3·13	8·51
	Zanamivir	343	0·40–5·11	0·93	1·11	1·32	0·39	2·49	342	0·40–2·38	1·14 ± 0·32	1·11

^*Tested isolates, including outliers.

^**Minimum to maximum IC₅₀ values, all viruses.

^***Q1: first quartile (25th percentile), all viruses.

^†Median (Q2): second quartile (50th percentile), all viruses.

^††Q3: Third quartile (75th percentile; X_0·75), all viruses.

^†††IQR: Interquartile range (IQR=Q3-Q1).

^‡Statistical IC₅₀ cutoff for NAI susceptibility, set at 3 interquartile ranges (3IQR) from the 75th percentile (=X_0·75 + 3IQR). Outliers with IC₅₀ above cutoff and >10-fold mean IC₅₀ of drug were characterized as extreme outliers. Mild outliers were isolates with IC₅₀ >X_0·75 + 3IQR, but >2-fold <10-fold that of the mean IC₅₀ of the drug.

^‡‡Number of isolates analyzed to determine mean and median drug IC₅₀s, outliers excluded.

^‡‡‡Minimum to maximum IC₅₀ values, outliers excluded.

^§Mean and standard deviation (SD) of IC₅₀ values, outliers excluded.

^§§Median of IC₅₀ values, outliers excluded.