Infections respiratoires grippales chez les patients immunodéprimés

Myxovirus influenza is an ubiquitous enveloped single-stranded RNA virus causing mostly upper respiratory tract infections but even lower in the most fragile patients. Despite growing concern about a new pandemic, seasonal influenza is responsible for severe morbidity and mortality and considerable socioeconomic impact. Influenza-related complications may be pulmonary, non-pulmonary or due to exacerbation of an underlying cardiopulmonary disease, the latter accounting for the majority of influenza-related mortality. Long underestimated in the immunocompromised, influenza is now recognized as a true opportunistic respiratory pathogen in these patients. Its real incidence in immunocompromised patients is not known but may be quite high because comparable to that of the general population, true reservoir of virus for these patients. In the immunocompromised, influenza features a higher rate of low respiratory tract involvement, as high as a third of cancer and pulmonary transplanted patients. These influenza-related pneumonia may be either primary viral or secondary to bacterial and fungal lung superinfection that must be systematically investigated. They may confine to acute respiratory failure with a consistently high mortality rate. Antiviral therapy of influenza has not been evaluated in the immunocompromised patients. The lack of a proven therapy emphasizes the essential importance of influenza prevention in these patients. Influenza epidemics have been reported in wards taking care of immunocompromised patients and isolation procedures are necessary to limit nosocomial spread of the virus. Nevertheless, immunization remains the cornerstone of influenza prevention. The possible reduced efficiency and the lack of clinical evaluation of influenza vaccine in the immunocompromised underline the critical importance of household contacts and health-care workers' immunization to reduce influenza transmission. Despite the high incidence worldwide of influenza, the physiopathology of influenza-related pneumonia remains poorly understood. Studies evaluating direct pathogenic effects of the virus on the alveolar epithelium or the susceptibility to lung superinfection secondary to bronchial epithelial injury caused by influenza are warranted and may help to determine the role for preemptive or curative antiviral therapy.