4. A(H3N2) viruses showing RI or HRI
Nine (0.3%) A(H3N2) viruses out of 2574 tested showed RI or
HRI by oseltamivir or zanamivir (Fig. 2 and Table 1). Three of these
had a NA Q136K amino acid substitution (Table 1). Available clinical
specimens yielding two of these isolates did not contain the
mutation conferring the amino acid substitution prior to cell culture.
However, NA Q136K substitution has been reported previously
in clinical specimens (Dapat et al., 2010). One A(H3N2) virus
from the United States contained a NA E119V substitution which
conferred HRI by oseltamivir but had no effect on susceptibility
to the other NAIs. The E119V variant virus came from an oseltamivir-
treated patient. The NA E119V substitution was detected in the
corresponding clinical specimen. NA amino acid substitutions
T148K, N329K, S331R and V215I were detected in viruses with
IC50 fold-change values that were close to the intersect between
NI and RI categories for oseltamivir and/or zanamivir. NA T148K
and D151G substitutions can emerge during culturing of
A(H3N2) viruses (Tamura et al., 2013).