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Resumen Introduccion La pandemia de gripe de 2009 tuvo una gran repercusion social. Se dedicaron muchos recursos sanitarios a la atencion medica, la prevencion y la vigilancia epidemiologica. La vigilancia epidemiologica se sustenta en la notificacion de casos de sindrome gripal y de casos confirmados de gripe. El objetivo fue la estimacion de la incidencia real de sindrome gripal durante la pandemia de gripe de 2009. Metodos Sistema de captura-recaptura durante el mes de mayor incidencia en Castellon. Se utilizaron 2 sistemas de informacion: a) sistema electronico de notificacion de enfermedades de declaracion obligatoria (EDO), y b) datos de laboratorio (LAB). Las estimaciones se han realizado estratificando por grupo de edad y semana. Se calculo el coeficiente de independencia en estos estratos. Resultados En total se identificaron 7.181 casos EDO y 524 LAB, de los que 211 coincidian en ambos sistemas. La estimacion total fue de 17.785 casos en un mes. Ello significa que en el periodo estudiado casi el 4% de las personas del area sufrieron un cuadro gripal (incidencia acumulada), y aproximadamente una de cada 100 personas estuvo diariamente afectada (prevalencia diaria). Acudieron a consulta de atencion primaria (EDO) un 40% de los afectados (sensibilidad del sistema EDO). Conclusiones Para obtener una estimacion de la incidencia real en la poblacion durante la pandemia habria que multiplicar la cifra de consultas medicas por un factor de 2,5. Este factor es inferior al estimado en periodos sin alerta pandemica.

Introduction The influenza pandemic of 2009 had a great social impact. Many health resources were devoted to the care, prevention and surveillance of this disease. Epidemiological surveillance is based on the reporting of cases of influenza-like illness (ILI) and confirmed influenza cases. The objective was to estimate the true incidence of ILI during the influenza pandemic of 2009. Methods The capture–recapture method was applied during the month of highest influenza incidence in Castellon. Two notification systems were used: (i) electronic reporting of Notifiable Diseases (ND), and (ii) laboratory-based (LAB) data collection. Estimates were made by stratifying by age group and week. Independence coefficients were calculated for those strata. Results No dependence was found between stratification variables and the reporting system. A total of 7181 ND cases and 524 LAB cases were identified, of which 211 were recorded in both systems. The estimated total of cases was 17 785 in a single month. In the study period, almost 4% of people in the area suffered flu symptoms (cumulative incidence), with 1% being affected each day (daily prevalence). The sensitivity of the ND system was 40%, i.e., the percentage of patients seeking primary care. Conclusions To obtain an estimate of the actual incidence of influenza-like illness in the population during a pandemic period, the number of medical consultations should be multiplied by a factor of 2.5. This factor is lower than that estimated for periods without pandemic alert.

We estimate the impact of the two previous influenza seasonal vaccines and the pandemic vaccine on risk of A (H1N1) 2009 laboratory confirmed hospitalizations during the autumn 2009 pandemic wave in Castellón, Spain. We conducted a test-negative, hospital-based, case-control study. Influenza A (H1N1) 2009 infection was detected in 147 (44%) of 334 patients hospitalized for a presumptive influenza related illness. No effect was observed for the 2008-2009 and 2009-2010 seasonal influenza vaccines. However, the pandemic vaccine was associated with an adjusted vaccine effectiveness of 90% (95% CI, 48-100%). Pandemic vaccines were effective in preventing pandemic influenza associated hospitalizations.

Javier Buesa Gómez (Javier.Buesa@uv.es) Se describen las intervenciones llevadas a cabo en una unidad de epidemiología local, durante varios años, relacionadas con la epidemiología de la gastroenteritis por norovirus en residencias de ancianos de Castellón. Desde varios brotes acaecidos en un mismo geriátrico, hasta el estudio de los casos esporádicos que determinan la situación endémica en varias residencias. Este trabajo se centra en el análisis de esa situación endémica de síntomas digestivos en periodos de silencio epidémico y la propuesta de un método sencillo para detectar el inicio de brotes de GEA de transmisión progresiva (persona-persona) que hemos denominado Sistema de Detección por Umbral de Prevalencia (SiDUP). Se discute el espectro epidemiológico de la gastroenteritis por norovirus en estas instituciones para personas mayores. We describe the interventions carried out in a local epidemiology unit related to the epidemiology of gastroenteritis due to norovirus in geriatric homes in Castellón (Spain) during several years. These range from various outbreaks in the same geriatric home to the study of sporadic cases which determine the endemic situation. This study focuses on the analysis of this endemic situation of digestive symptoms in silent epidemic periods and proposes a simple method to detect the initiation of GEA of progressive transmission (person-person) which we call System of Detection by Prevalence Threshold (SiDUP). The epidemiological spectrum of gastroenteritis due to norovirus in geriatric homes is discussed.