Pandemic (H1N1) 2009 influenza: surveillance methodology

Information on how the number of cases of pandemic (H1N1) 2009 influenza has been estimated, following the introduction of the National Pandemic Flu Service, is provided in the methodology documents.

• Synopsis of the method used to estimate the number of pandemic influenza (H1N1) 2009 cases in England in the week 21 to 27July 2009 (PDF, 51 KB)
  The method currently used to obtain an estimate of the number of pandemic influenza (H1N1) 2009 cases relies on data from two surveillance systems: the QSurveillance® scheme, that provides an estimate of numbers consulting a GP with influenza-like illness (ILI); and the Royal College of General Practitioners (RCGP) and HPA Regional Microbiology Network scheme for swabbing clinically diagnosed cases.
  Added/updated: 25 November 2009
  
• Method used to estimate new pandemic (H1N1) 2009 influenza cases in England in the week 3 August to 9 August 2009 (PDF, 35 KB)
  An amended method is used to estimate the number of pandemic cases, which incorporates data from National Pandemic Flu Service (NPFS) and GP consultations.
  Added/updated: 25 November 2009