Open Access Research article

Impact of flu on hospital admissions during 4 flu seasons in Spain, 2000–2004

Annick D Lenglet12, Victoria Hernando2*, Pilar Rodrigo2, Amparo Larrauri3, Juan DM Donado3 and Salvador de Mateo3

Author Affiliations

1 European Programme for Intervention Epidemiology Training (EPIET), Smittskyddinstitutet/EPI, Nobels Vag 18, 17182, Solna, Sweden

2 Programa de Epidemiología Aplicada de Campo (PEAC), National Centre for Epidemiology, Public Health Institute Carlos III, C/Sinesio Delgado, 6 28029 Madrid, Spain

3 Epidemiological Surveillance, National Centre for Epidemiology, Public Health Institute Carlos III, C/Sinesio Delgado, 6 28029 Madrid, Spain

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BMC Public Health 2007, 7:197  doi:10.1186/1471-2458-7-197

Published: 8 August 2007



Seasonal flu epidemics in the European region cause high numbers of cases and deaths. Flu-associated mortality has been estimated but morbidity studies are necessary to understand the burden of disease in the population. Our objective was to estimate the excess hospital admissions in Spain of diseases associated with influenza during four epidemic influenza periods (2000 – 2004).


Hospital discharge registers containing pneumonia, chronic bronchitis, heart failure and flu from all public hospitals in Spain were reviewed for the years 2000 to 2004. Epidemic periods were defined by data from the Sentinel Surveillance System. Excess hospitalisations were calculated as the difference between the average number of weekly hospitalisations/100,000 in epidemic and non-epidemic periods. Flu epidemics were defined for seasons 2001/2002, 2002/2003, 2003/2004.


A(H3N2) was the dominant circulating serotype in 2001/2002 and 2003/2004. Negligible excess hospitalisations were observed during the 2002/2003 epidemic where A(H1N1) was circulating. During 2000/2001, flu activity remained below threshold levels and therefore no epidemic period was defined. In two epidemic periods studied a delay between the peak of the influenza epidemic and the peak of hospitalisations was observed. During flu epidemics with A(H3N2), excess hospitalisations were higher in men and in persons <5 and >64 years higher than 10 per 100,000. Pneumonia accounted for 70% of all flu associated hospitalisations followed by chronic bronchitis. No excess flu-specific hospitalisations were recorded during all seasons.


Flu epidemics have an impact on hospital morbidity in Spain. Further studies that include other variables, such as temperature and humidity, are necessary and will deepen our understanding of the role of each factor during flu epidemics and their relation with morbidity.