Abstract
During the 2009/10 pandemic, a national surveillance system for severe influenza cases was set up in France. We present results from the system's first four years. All severe influenza cases admitted to intensive care units (ICU) were reported to the Institut de Veille Sanitaire using a standardised form: data on demographics, immunisation and virological status, risk factors, severity (e.g. acute respiratory distress syndrome (ARDS) onset, mechanical ventilation, extracorporeal life support) and outcome. Multivariate analysis was performed to identify factors associated with ARDS and death. The number of confirmed influenza cases varied from 1,210 in 2009/10 to 321 in 2011/12. Most ICU patients were infected with A(H1N1)pdm09, except during the 2011/12 winter season when A(H3N2)-related infections predominated. Patients' characteristics varied according to the predominant strain. Based on multivariate analysis, risk factors associated with death were age ≥65 years, patients with any of the usual recommended indications for vaccination and clinical severity. ARDS occurred more frequently in patients who were middle-aged (36-55 years), pregnant, obese, or infected with A(H1N1)pdm09. Female sex and influenza vaccination were protective. These data confirm the persistent virulence of A(H1N1)pdm09 after the pandemic and the heterogeneity of influenza seasons, and reinforce the need for surveillance of severe influenza cases.
Highlights
The epidemiological surveillance of influenza in France has mainly been carried out in general practice, through two networks: the Réseau des Grog [1] and Sentinelles [2]
Data collected were restricted to a one-page standardised notification form which was forwarded to the InVS regional offices (Cire)
We used the first four years of intensive care unit (ICU) surveillance to describe and compare patient characteristics according to the season and the influenza virus circulating, and we looked at the risk factors associated with death and acute respiratory distress syndrome (ARDS)
Summary
The epidemiological surveillance of influenza in France has mainly been carried out in general practice, through two networks: the Réseau des Grog [1] and Sentinelles [2]. Biological confirmation relied on a positive influenza reverse transcriptase-PCR (RT-PCR) performed on a respiratory sample This ICU surveillance was maintained after the pandemic season. In order to reach a high level of notification, each of the 17 Cires regularly contact the ICUs in their own region to ensure that all influenza cases are reported, to complete the missing information and to follow patients’ evolution until ICU discharge or death. They regularly matched the ICUs surveillance data with the hospital virological database. The adult and paediatric French Societies of Anaesthesia and Critical Care Medicine provided strong support for this surveillance
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