Surveillance design

At the request of the Spanish Agency of Medicines and Medical Devices (Agencia Española de Medicamentos y Productos Sanitarios/AEMPS), the National Centre for Epidemiology, acting as a Central Unit, contacted network members in August 2009 and re-established the network to detect a potential GBS outbreak related to A(H1N1)pdm09 vaccination. The eleven hospitals constituting the original network remained functionally appropriate for surveillance with minor changes in referral, staff and catchment population but one hospital which had difficulties in notifying cases was excluded. In Spain, a national health service covers the majority of population. To estimate incidence rates, each participant hospital updated the number of people it covered. Of a total of 36.9 million Spanish residents aged ≥20 years, the population under surveillance numbered 4.68 million, approximately 1/8 of the country population of that age. Prospective notification to the Central Unit of all patients suspected of presenting with GBS started in September 2009, approximately one month before onset of the A(H1N1) monovalent vaccine campaign, and ended on 31 December 2011. Retrospective reporting dated back to 1 January 2009. The Central Unit was tasked with identifying potential outbreaks on the basis of the information supplied by local neurologists, and, when applicable, notifying these to the AEMPS.