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Volume 29, Supplement 2, 22 July 2011, Pages B63-B69
Historical Influenza Pandemics
doi:10.1016/j.vaccine.2011.03.064 | How to Cite or Link Using DOI
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Burden of illness of the 2009 pandemic of influenza A (H1N1) in Denmark
K?re M?lbaka, Corresponding Author Contact Information, E-mail The Corresponding Author, Katarina Widgrena, b, Klaus Skovbo Jensenc, Steen Ethelberga, Peter H. Andersena, Annette H. Christiansena, Hanne-Dorthe Emborga, Sophie Gubbelsa, b, Katja Majlund Hardera, Tyra Grove Krausea, Anne Mazicka, Lars Peter Nielsend, Jens Nielsena, Palle Valentiner-Brantha and Steffen Glismanna
a Department of Epidemiology, Statens Serum Institut, Copenhagen, Denmark
b European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC) Stockholm, Sweden
c Department of Microbiological Surveillance and Research Statens Serum Institut, Copenhagen, Denmark
d Department of Virology, Statens Serum Institut, Copenhagen, Denmark
Received 9 November 2010;
revised 4 March 2011;
accepted 17 March 2011.
Available online 12 July 2011.
Abstract
We analysed Danish surveillance data to estimate influenza-associated morbidity and mortality in 2009. To obtain population-based estimates of the clinical attack rate, we combined data from two different primary health care surveillance systems, national numbers of the proportion of positive influenza tests, and data from a web-based interview on health care seeking behaviour during the pandemic. From a national registry, we obtained data on hospital admissions (ICD-10 codes) for influenza related conditions. Admission to intensive care was monitored by a dedicated surveillance scheme. Mortality was estimated among laboratory confirmed cases but was also expressed as excess all-cause mortality attributed to influenza-like illness in a multivariable time series analysis. In total, we estimated that 274,000 individuals (5%) in Denmark experienced clinical illness. The highest attack rate was found in children 5?14 years (15%). Compared with the expected number of hospital admissions, there was an 80% increase in number of influenza related hospital admissions in this age group. The numbers of patients admitted to intensive care approached 5% of the national capacity. Estimates of the number of deaths ranged from 30 to 312 (0.5?5.7 per 100,000 population) depending on the methodology. In conclusion, the pandemic was characterised by high morbidity and unprecedented high rates of admissions to hospitals for a range of influenza-related conditions affecting mainly children. Nonetheless, the burden of illness was lower than assumed in planning scenarios, and the present pandemic compares favourable with the 20th century pandemics.
Keywords: Pandemic influenza A (H1N1); Morbidity; Mortality; Burden of illness
Volume 29, Supplement 2, 22 July 2011, Pages B63-B69
Historical Influenza Pandemics
doi:10.1016/j.vaccine.2011.03.064 | How to Cite or Link Using DOI
Permissions & Reprints
Burden of illness of the 2009 pandemic of influenza A (H1N1) in Denmark
K?re M?lbaka, Corresponding Author Contact Information, E-mail The Corresponding Author, Katarina Widgrena, b, Klaus Skovbo Jensenc, Steen Ethelberga, Peter H. Andersena, Annette H. Christiansena, Hanne-Dorthe Emborga, Sophie Gubbelsa, b, Katja Majlund Hardera, Tyra Grove Krausea, Anne Mazicka, Lars Peter Nielsend, Jens Nielsena, Palle Valentiner-Brantha and Steffen Glismanna
a Department of Epidemiology, Statens Serum Institut, Copenhagen, Denmark
b European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC) Stockholm, Sweden
c Department of Microbiological Surveillance and Research Statens Serum Institut, Copenhagen, Denmark
d Department of Virology, Statens Serum Institut, Copenhagen, Denmark
Received 9 November 2010;
revised 4 March 2011;
accepted 17 March 2011.
Available online 12 July 2011.
Abstract
We analysed Danish surveillance data to estimate influenza-associated morbidity and mortality in 2009. To obtain population-based estimates of the clinical attack rate, we combined data from two different primary health care surveillance systems, national numbers of the proportion of positive influenza tests, and data from a web-based interview on health care seeking behaviour during the pandemic. From a national registry, we obtained data on hospital admissions (ICD-10 codes) for influenza related conditions. Admission to intensive care was monitored by a dedicated surveillance scheme. Mortality was estimated among laboratory confirmed cases but was also expressed as excess all-cause mortality attributed to influenza-like illness in a multivariable time series analysis. In total, we estimated that 274,000 individuals (5%) in Denmark experienced clinical illness. The highest attack rate was found in children 5?14 years (15%). Compared with the expected number of hospital admissions, there was an 80% increase in number of influenza related hospital admissions in this age group. The numbers of patients admitted to intensive care approached 5% of the national capacity. Estimates of the number of deaths ranged from 30 to 312 (0.5?5.7 per 100,000 population) depending on the methodology. In conclusion, the pandemic was characterised by high morbidity and unprecedented high rates of admissions to hospitals for a range of influenza-related conditions affecting mainly children. Nonetheless, the burden of illness was lower than assumed in planning scenarios, and the present pandemic compares favourable with the 20th century pandemics.
Keywords: Pandemic influenza A (H1N1); Morbidity; Mortality; Burden of illness
