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. 2010 Mar 4;5(3):e9533. doi: 10.1371/journal.pone.0009533

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This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

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Data was compiled from VA's Electronic Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE). Diagnosis codes from outpatient and emergency department visits are analyzed for total number of patients with influenza-like Illness (ILI). Visits are counted as ILI if their diagnostic code is fever, an included respiratory code, or unspecified viral illness. A complete list of ICD-9-CM codes for the ILI category can be found in Table 1. Counts do not represent confirmed influenza cases. (A) VA outpatient visits for ILI from the ESSENCE from Sept 28, 2008-July 31, 2009 (corresponding to CDC 2008–2009 flu season weeks 40–30). (B) VA outpatient visits for ILI from ESSENCE, April 1, 2009-July 31, 2009 (corresponding to CDC 2008–2009 flu season weeks 13–30). Arrow points to the start of pandemic H1N1 2009.