COMMON EMERGENCE OF AMANTADINE-RESISTANT AND RIMANTADINE-RESISTANT INFLUENZA-A VIRUSES IN SYMPTOMATIC IMMUNOCOMPROMISED ADULTS

The importance and significance of amantadine-or rimantadine-resistant influenza viruses in immunocompromised patients was studied in a popu lation of adult bone marrow transplant (BR IT) recipients and patients with leukemia prospectively cultured for respiratory viruses. Influen za A viruses were isolated from 29 patients with acute respiratory ill ness (14 BMT recipients and 15 patients with leukemia). Fifteen patien ts (52%) received amantadine(n = 4) or rimantadine (n = 11) therapy. A ll influenza isolates recovered from six patients shedding virus for g reater than or equal to 3 days were screened for antiviral susceptibil ity; resistant isolates were further genetically characterized. Initia l influenza isolates were susceptible to amantadine or rimantadine, bu t subsequent isolates from five of six patients were resistant. Influe nza-associated mortality was similar among patients with and without d ocumented antiviral resistance (2 of 5 vs. 5 of 24). We conclude that development of antiviral resistance in immunocompromised individuals s hould be considered when they have been treated with antivirals and ha ve shed influenza virus for a prolonged period. Isolation procedures s hould be instituted for all immunocompromised patients with influenza, both during and after therapy with amantadine or rimantadine.