Background: Pandemic 2009 influenza A/H1N1 (H1N1v) is resistant to adamantanes, leaving neuraminidase inhibitors as the only therapeutic option. Other mutations are considered to be associated with virulence and clinical severity. However, out of the surveillance programs, few studies analyze the presence of resistance/virulent H1N1v variants in certain clinical circumstances.
Objectives: To define the frequency and role of resistance and virulence mutations in a specific clinical circumstance-in patients with persistent infection by H1N1v.
Study design: Observational study of patients with persistent H1N1v infection admitted to our hospital.
Results: NAI-resistance mutations were detected in 14.3% of cases with persistent infection (2/14), and in none of the non-persistent controls (0/15). These cases were initially infected with susceptible variants that acquired resistance at different time-points after therapy with oseltamivir (OTV). The first case (case 2) was an HIV-positive patient who rapidly acquired resistance 9 days after diagnosis (6 days on OTV) and whose infection resolved after standard OTV therapy. The second case (case 3) was a patient with chronic lymphocytic leukemia [corrected] and the longest viral persistence (59 days). The resistance mutation was detected in the specimen taken on day 37 after diagnosis (30 days on OTV). Once the resistance mutation was identified, OTV was substituted by zanamivir and the infection resolved. In addition to mutations encoding resistance, variants associated with virulence were also sought. The D225G mutation was not found in any case, whereas the D225E variant was identified in three persistent cases but also in two non-persistent ones. In one patient, the D225E substitution coincided with the H275 resistant mutation.
Conclusions: NAI-resistance mutations were detected, at rather different paces, in non-severe immunosuppressed cases with persistent infection by influenza A/H1N1v.
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