Epidemiology, prevention, and management of influenza in patients with hematologic malignancy.

Influenza results in annual epidemics of respiratory viral illness during the winter; when a novel virus enters the human population, a pandemic may result with a larger proportion of the population sickened. Unlike the mild and typically self-limited disease seen in immunocompetent patients, immunocompromised patients frequently have a more severe course. These individuals shed virus for a prolonged period of time, have a high rate of viral pneumonia, more frequently develop bacterial and fungal super-infections, and may develop late-onset airflow obstruction. Further, antiviral resistance develops more frequently in immunosuppressed patients. Although the cornerstone of prevention of influenza is vaccination, vaccine efficacy in patients with hematologic malignancies, particularly stem cell transplant recipients, is poor. Alternative preventative measures, such as seasonal antiviral prophylaxis can be considered. Lastly, there have been no prospective studies of antivirals in the management of influenza infections in these patients. As such, the optimal regimen and duration remains to be defined. Available evidence suggests that prolonged course are frequently needed. Patients who fail to response or have relapsed infections should be tested for emergence of antiviral resistance and alternative diagnoses should be investigated.