Prolonged Excretion of Amantadine-Resistant Influenza A Virus Quasi Species after Cessation of Antiviral Therapy in an Immunocompromised Patient

Phenotypic and molecular studies were conducted to characterize multiple influenza A isolates recovered from an immunocompromised patient who died of viral and fungal pneumonitis. The recovery of amantadine-resistant isolates was correlated with the detection of 2 drug-resistant M2 variants (codons 27 and 31) in combination with a wild-type virus. The mutant viruses persisted within the viral population in variable proportions µ1 month after cessation of antiviral therapy. These results confirm animal studies reported elsewhere regarding the genetic stability of influenza M2 mutants and their potential for transmission in humans.