Table 4.

Neuraminidase inhibitor susceptibility of 2009 pandemic H1N1 virus isolates (2008–2009 season).

NAI	Pandemic H1N1 virus isolates	Isolates analyzed (n)*	IC50 (nM)a
			Range	Mean (±SD)b	Median	IQRc	X0.75d	Statistical Cutoff e
Oseltamivir	H275 wildtypef	2243	0.05–1.78	0.25±0.11	0.24	0.08	0.28	0.52
	H275Y variantsg	14	54.21–155.00	87.57±25.53	80.30	--	--	--
Zanamivir	H275 wildtypef	2233	0.08–1.03	0.31±0.08	0.30	0.11	0.36	0.69
	H275Y variantsg	14	0.27–0.53	0.38±0.08	0.36
Peramivir	H275 wildtype	538	0.03–0.35	0.08±0.04	0.07	0.04	0.10	0.22
	H275Y variants	11	8.1–12.91	10.40±1.37	10.29	--	--	--

^aDetermined in the chemiluminescent neuraminidase inhibition assay.

^*Outliers and mixes (comprising wildtype and variant populations) were excluded from the calculation of mean, SD and median of IC₅₀ values.

^bSD, standard deviation of IC₅₀ values.

^cIQR, interquartile range.

^dX_0.75, 75^th Percentile.

^eStatistical cutoff of IC₅₀ values for NAI susceptibility, determined by X_0.75 + 3IQR. Outliers with IC₅₀ above this cutoff and >10 times the mean IC₅₀ for each drug, were characterized as extreme outliers; those with known drug-resistance mutations such as H275Y were classified as resistant and analyzed separately.

^fH275 wildtype, oseltamivir-susceptible pandemic virus isolates.

^gH275Y variants, oseltamivir-resistant pandemic virus isolates.