Volume 25, Number 11—November 2019
Human-to-Human Transmission of Influenza A(H3N2) Virus with Reduced Susceptibility to Baloxavir, Japan, February 2019
|Influenza virus||Median IC50 + SD, nmol/L
|Baloxavir||NA inhibitors (WHO criteria)
|A/Kanagawa/IC18141/2019||236.08||0.37 (NI)||0.18 (NI)||1.01 (NI)||1.27 (NI)|
|A(H3N2) of 2018–19||1.27 + 1.08†||0.37 + 0.17‡||0.13 + 0.03‡||0.79 + 0.33‡||1.00 + 0.21‡|
*We determined antiviral susceptibilities using a focus reduction assay and a fluorescent NA inhibition assay (NA-Fluor Influenza Neuraminidase Assay Kit; Applied Biosystems, https://www.thermofisher.com) (4) and calculated IC50 values using MikroWin 2010 (Labsis, https://labsis.de). We expressed NA inhibitor susceptibilities using WHO criteria for influenza A virus inhibition, which define susceptibility on the basis of the -fold change in IC50 compared with the IC50 of reference isolates (6). WHO inhibition was defined as normal (<10-fold increase), reduced (10–100-fold increase), or highly reduced (>100-fold increase) in comparison with the median value of isolates from the same influenza season. IC50, 50% inhibitory concentration; NA, neuraminidase; NI, normal inhibition; WHO, World Health Organization.
†n = 83.
‡n = 170.
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