Amparo Larrauri Cámara

Epidemiology of the 2009 influenza pandemic in Spain. The Spanish Influenza Surveillance System

In accordance with European Centre for Disease Prevention and Control recommendations, the Spanish Influenza Surveillance System (SISS) maintained its activity during the summer of 2009, and since July 2009 the pandemic virus activity was monitored by the SISS. In this paper, we describe the epidemiological and virological characteristics of the 2009 pandemic in the Spain through the SISS. Spain experienced a transmission of the new A(H1N1)pdm09 influenza virus during the summer of 2009, which gradually increased, resulting in the pandemic wave in early autumn of that year. The reproductive number R0, estimated during the growth phase of the pandemic wave (1.32; 95% confidence interval [95%CI], 1.29-1.36), showed a transmissibility comparable to preceding pandemics. There was an almost complete replacement of the previous seasonal A(H1N1) influenza virus by the pandemic virus A(H1N1)pdm09. The pandemic virus produced a greater burden of illness than seasonal influenza in children younger than 15 years old, while the incidence in those older than 64 years was lower compared with previous inter-pandemic seasons. Nevertheless, in Spain the 2009 pandemic was characterized as mild, considering the duration of the pandemic period and the influenza detection rate, both in the range of those observed in previous inter-pandemic seasons. Also, the case fatality ratio (CFR) was estimated at 0.58 deaths/1,000 confirmed ILI cases (95%CI, 0.52-0.64), in the range of the two previous pandemics of 1957 and 1968, with the highest CFR observed in the older than 64 years age group. In the 2009 pandemic there was a higher percentage of pandemic confirmed deaths in the younger ages, compared to seasonal influenza, since only 28% of the reported deaths occurred in persons aged 64 years and older.

Transmisibilidad y gravedad de la pandemia de gripe A(H1N1)2009 en España

OBJECTIVES To estimate the value of the basic reproduction number for the pandemic wave of influenza A (H1N1) 2009 in Spain and to assess its impact on morbidity and mortality in the Spanish population compared with those in the previous influenza season. METHODS Data on the incidence of influenza and viral detections were obtained from the Spanish Influenza Surveillance System. Deaths from pandemic influenza were obtained from the Coordinating Center for Health Alerts and Emergencies of the Spanish Ministry of Health and Social Policy, and deaths from seasonal influenza during the period 2003-2008 were obtained from the National Statistics Institute. The reproduction number was estimated by two methods: firstly, by using the growth rate of the cumulative incidence of influenza during the exponential growth phase of the pandemic wave, and secondly (maximum likelihood estimation), through analysis the dates of onset of symptoms observed in pairs of cases based on generation time distribution. We calculated the fatality rate and mortality from influenza by comparing potential years of life lost in the pandemic season with those in previous interpandemic seasons. RESULTS The start of the pandemic wave occurred in Spain earlier in week 40/2009 (from 4 to 10 October), with an absolute predominance of the new strain in the pattern of circulating viruses. The value of R(0) in the growth phase of the wave was 1.29 (95% CI: 1.25-1.33), estimated with the first method, and was 1.01 (95% CI: 0.99-1.03) with the second method. During the pandemic season, there were 318 deaths from pandemic influenza, affecting younger age groups than in previous interpandemic seasons. Consequently, the number of potential years of life lost in the pandemic season (11,612) was estimated at six times the adjusted annual average of the interpandemic influenza seasons for comparison (1,802). CONCLUSIONS The estimates of R(0) for the growth phase of the pandemic wave were in the lower range of estimates of this parameter in previous pandemics. Mortality indicators calculated in the pandemic period showed an increase in deaths compared with previous interpandemic seasons, which was most pronounced in young patients.

VIGILANCIA DE LA PANDEMIA DE GRIPE (H1N1) 2009 EN ESPAÑA

Fundamento: Espana experimento una circulacion del nuevo virus de la gripe (H1N1)2009 durante el verano de 2009, que evoluciono de forma creciente hasta la presentacion a principios del otono de la primera onda pandemica por dicho virus. Los objetivos de este trabajo son describir la evolucion de esta onda pandemica en nuestro pais y evaluar su impacto en la morbilidad y mortalidad de la poblacion espanola. Metodo: A partir de la informacion proporcionada por el Sistema de Vigilancia de la Gripe en Espana y el Centro de Coordinacion de Alertas y Emergencias del Ministerio de Sanidad y Politica Social se han estimado una serie de indicadores epidemiologicos y virologicos para evaluar el nivel de actividad e intensidad de la onda pandemica, asi como su gravedad. Resultados: La onda pandemica por el virus (H1N1)2009 se inicio a comienzos del otono de 2009 y registro valores maximos de incidencia de gripe de 372,15 casos semanales/100.000 habitantes. Las mayores tasas de incidencia de gripe se observaron en los menores de 15 anos. La tasa de deteccion viral en el periodo pandemico se mantuvo en el rango de las registradas previamente (46,4%). Se estimo una tasa de letalidad global de 0,43 defunciones por 1.000 casos de gripe pandemica. Un 64% de las defunciones por gripe pandemica se registraron en adultos jovenes, con maximas tasas de mortalidad en el grupo de 45-64 anos (9,35 defunciones/1.000.000 habitantes). La mortalidad asociada a gripe estacional en el periodo 2001-2008 fue maxima en los mayores de 64 anos (95% del total de defunciones). Conclusiones: La onda pandemica por el virus de la gripe (H1N1)2009 tuvo una presentacion precoz en Espana y una intensidad media en comparacion con las trece ondas estacionales previas de gripe. Esta primera onda tambien se caracterizo por un caracter leve, teniendo en cuenta tasas de letalidad o mortalidad, si bien un elevado porcentaje de las defunciones confirmadas por el nuevo virus se ha observado en menores de 65 anos.

EXCESO DE MORTALIDAD PRECOZ RELACIONADO CON LA GRIPE EN ESPAÑA DURANTE UN PERIODO INTERPANDÉMICO

Fundamentos: El indicador Anos Potenciales de Vida Perdidos (APVP) ha sido utilizado con frecuencia en analisis de mortalidad precoz, y recientemente ha servido para estimar el impacto de la ultima pandemia de gripe A(H1N1)pdm09. El objetivo de este estudio ha sido estimar los excesos de defunciones por gripe y neumonia (GyN) en Espana y los APVP durante el periodo 1980-2008, valorando la mortalidad atribuible a gripe en funcion del tipo/subtipo de virus predominante. Metodos: Los excesos de defunciones mensuales se calcularon con modelos de regresion ciclica. El calculo de APVP se realizo como el producto del numero de excesos de defunciones por la diferencia entre la esperanza de vida al nacer y los anos vividos para cada grupo de edad. El analisis de la variacion entre los excesos de defunciones por GyN y APVP, segun el tipo/subtipo de virus de la gripe predominante, se llevo a cabo con un analisis de regresion de Poisson. Resultados: En las temporadas con predominio del virus de la gripe A(H3) el promedio de excesos de defunciones por GyN se estimo en 1.348 y de APVP en 5.297, mientras que en las temporadas con predominio de A(H1) o B el promedio de excesos por las mismas causas fue de 648 y de APVP de 2.885. Las razones de tasas ajustadas de excesos (2,11; IC-95%=2,05-2,16) y de APVP (1,86; IC-95%=1,83-1,88) senalaron que las frecuencias relativas de ambos indicadores son significativamente mayores en las temporadas con predominio de virus de la gripe A(H3). Conclusiones: Los excesos de defunciones y APVP se duplicaron al comparar las temporadas con predominio del subtipo A(H3) frente al resto de virus de la gripe.

Transmissibility and severity of the pandemic influenza A (H1N1) 2009 virus in Spain

OBJECTIVES: To estimate the value of the basic reproduction number for the pandemic wave of influenza A (H1N1) 2009 in Spain and to assess its impact on morbidity and mortality in the Spanish population compared with those in the previous influenza season. METHODS: Data on the incidence of influenza and viral detections were obtained from the Spanish Influenza Surveillance System. Deaths from pandemic influenza were obtained from the Coordinating Center for Health Alerts and Emergencies of the Spanish Ministry of Health and Social Policy, and deaths from seasonal influenza during the period 2003-2008 were obtained from the National Statistics Institute. The reproduction number was estimated by two methods: firstly, by using the growth rate of the cumulative incidence of influenza during the exponential growth phase of the pandemic wave, and secondly (maximum likelihood estimation), through analysis the dates of onset of symptoms observed in pairs of cases based on generation time distribution. We calculated the fatality rate and mortality from influenza by comparing potential years of life lost in the pandemic season with those in previous interpandemic seasons. RESULTS: The start of the pandemic wave occurred in Spain earlier in week 40/2009 (from 4 to 10 October), with an absolute predominance of the new strain in the pattern of circulating viruses. The value of R(0) in the growth phase of the wave was 1.29 (95% CI: 1.25-1.33), estimated with the first method, and was 1.01 (95% CI: 0.99-1.03) with the second method. During the pandemic season, there were 318 deaths from pandemic influenza, affecting younger age groups than in previous interpandemic seasons. Consequently, the number of potential years of life lost in the pandemic season (11,612) was estimated at six times the adjusted annual average of the interpandemic influenza seasons for comparison (1,802). CONCLUSIONS: The estimates of R(0) for the growth phase of the pandemic wave were in the lower range of estimates of this parameter in previous pandemics. Mortality indicators calculated in the pandemic period showed an increase in deaths compared with previous interpandemic seasons, which was most pronounced in young patients.

Excesos de mortalidad en España durante la transmisión de gripe pandémica en el año 2009

Background: The Spanish daily mortality monitoring system and the program «European monitoring of excess mortality for public health action» found two excesses of mortality in Spain in November and December 2009. Methods: We analyzed the evolution of mortality in Spain during those months using time-series analysis methods based on historical mortality series and compared it in the time with influenza transmission. Results: Observed mortality for the total population was higher than expected in two periods: weeks 46-47/2009 with 5.75% excess and weeks 51-52/2009 with 7.35% excess. Observed mortality higher than expected, was also observed in children 5-14 years old during weeks 46-48/2009 with 41 deaths vs 21 expected. Exces mortality in November occurred before or was concomitant with highest influenza incidence rates. Excess mortality in December occurred five weeks after the influenza incidence peak and along with dramatic drop in temperatures. RSV and traffic accidents were ruled out as factor associated to these excesses. Conclusions: While temperatures could explain most of the excess mortality observed in December, no single factor could be associated with observed excess mortality in November.

Estudio cycEVA: casos y controles para la estimación de la efectividad de la vacuna antigripal en España, 2008-2013

Background: In Spain, influenza vaccine effectiveness (EV) is estimated since 2008-09 season through the cycEVA case-control study, the Spanish component of the European I-MOVE (Monitoring Influenza Vaccine Effectiveness in the EU/EEA) network. We aimed at describing cycEVA performance in its five consolidated editions 2008/09 -; 2012/13. Methods: During the study period the following indicators were analysed: 1) the participation of sentinel general practitioners and pediatricians (MP), 2) the population studied and the study period, 3) the data quality and 4) the dissemination of the cycEVA results. Trend analysis of the indicators was done using the Cochran-Armitage test to compute the Annual Percentage Change (PCA). Results: The number of participating MP increased from 164 in 2008-09 to 246 in the following editions. The percentage of MP recruiting at least one patient increased significantly annually (PCA = 15.33%). The percentage of recruited patients included into the analysis increased (PCA=5.91%) from 77% in 2008-09 to more than 95% in the following editions. The percentage of cycEVA patients contributing to the I-MOVE study ranged between 23% and 30% in the pilot and 2011-12 editions respectively.. Final results were disseminated in quartile 2 peer-reviewed journals and 2010-11 and 2011-12 preliminary EV estimates were published in quartile 1 journals. cycEVA publications received 97 citations. Conclusion: cycEVA study achieved more quality information, timely EV estimates and a higher impact of the results.