Incidence of H1N1v Influenza-like Illness and Risk Factors for Serious Influenza Forms in HIV Infected Patients

To estimate the incidence of H1N1v influenza-like illness and to study the risk factors for serious influenza forms during pandemic period in French HIV infected patients.

* Definitions:

* Influenza like illness is defined as fever> 37°8C and cough or pharyngalgia. (Centers for Disease Control definition). * Serious forms of influenza-like illness is defined by hospitalization within 14 days onset of symptoms or death attributed to influenza like illness. * Design:

* Survey sampling for estimating H1N1v influenza-like illness incidence. * Out of approximately 50 000 patients under follow-up in one of the 40 ANRS centres, a sub-group will be selected by random sampling. Sampling will be stratified by centre and sampling fraction per site will vary in order to select 60 to 80 patients for this study per site. A total of 2500 to 3000 patients will be selected to allow for estimating the incidence of H1N1v influenza-like illness with an adequate precision.

Selected patients will be asked to contact the clinical staff on site as soon as any influenza like symptoms appear. In the case of influenza like illness patients are requested to attend to the clinic within 24 hours for physical examination and naso-pharyngeal swab for diagnosis of A(H1N1)v infection.

Nested case-control study for the determination of risk factors for serious forms:

* Cases: Serious forms (see definition above) identified by any clinical site or hospitalisation unit. * Controls: Patients of the randomly selected sample (see survey sampling above), presenting with influenza-like illness without any criterion for severity.

Exhaustivity check:

The exhaustivity of symptomatic forms will be assessed a posteriori by merging information from all available data sources.