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Volume 25, Number 11—November 2019
Dispatch

Human-to-Human Transmission of Influenza A(H3N2) Virus with Reduced Susceptibility to Baloxavir, Japan, February 2019

Emi TakashitaComments to Author , Masataka Ichikawa, Hiroko Morita, Rie Ogawa, Seiichiro Fujisaki, Masayuki Shirakura, Hideka Miura, Kazuya Nakamura, Noriko Kishida, Tomoko Kuwahara, Hiromi Sugawara, Aya Sato, Miki Akimoto, Keiko Mitamura, Takashi Abe, Masahiko Yamazaki, Shinji Watanabe, Hideki Hasegawa, and Takato Odagiri
Author affiliations: National Institute of Infectious Diseases, Tokyo, Japan (E. Takashita, H. Morita, R. Ogawa, S. Fujisaki, M. Shirakura, H. Miura, K. Nakamura, N. Kishida, T. Kuwahara, H. Sugawara, A. Sato, M. Akimoto, S. Watanabe, H. Hasegawa, T. Odagiri); Ichikawa Children’s Clinic, Kanagawa, Japan (M. Ichikawa); Eiju General Hospital, Tokyo (K. Mitamura); Abe Children’s Clinic, Kanagawa (T. Abe); Zama Children’s Clinic, Kanagawa (M. Yamazaki)

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Table 2

Susceptibility of influenza A(H3N2) virus carrying polymerase acidic I38T substitution detected in children within family cluster, February 2019, compared with 2018–19 seasonal virus, Japan*

Influenza virus Median IC50 + SD, nmol/L
Baloxavir NA inhibitors (WHO criteria)
Oseltamivir Peramivir Zanamivir Laninamivir
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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Page updated: October 16, 2019
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