Excess mortality related to seasonal influenza and extreme temperatures in Denmark, 1994-2010.

BACKGROUND: In temperate zones, all-cause mortality exhibits a marked seasonality, and one of the main causes of winter excess mortality is influenza. There is a tradition of using statistical models based on mortality from respiratory illnesses (Pneumonia and Influenza: PI) or all-cause mortality for estimating the number of deaths related to influenza. Different authors have applied different estimation methodologies. We estimated mortality related to influenza and periods with extreme temperatures in Denmark over the seasons 1994/95 to 2009/10. METHODS: We applied a multivariable time-series model with all-cause mortality as outcome, activity of influenza-like illness (ILI) and excess temperatures as explanatory variables, controlling for trend, season, age, and gender. Two estimates of excess mortality related to influenza were obtained: (1) ILI-attributable mortality modelled directly on ILI-activity, and (2) influenza-associated mortality based on an influenza-index, designed to mimic the influenza transmission. RESULTS: The median ILI-attributable mortality per 100,000 population was 35 (range 6 to 100) per season which corresponds to findings from comparable countries. Overall, 88% of these deaths occurred among persons ≥ 65 years of age. The median influenza-associated mortality per 100,000 population was 26 (range 0 to 73), slightly higher than estimates based on pneumonia and influenza cause-specific mortality as estimated from other countries. Further, there was a tendency of declining mortality over the years. The influenza A(H3N2) seasons of 1995/96 and 1998/99 stood out with a high mortality, whereas the A(H3N2) 2005/6 season and the 2009 A(H1N1) influenza pandemic had none or only modest impact on mortality. Variations in mortality were also related to extreme temperatures: cold winters periods and hot summers periods were associated with excess mortality. CONCLUSION: It is doable to model influenza-related mortality based on data on all-cause mortality and ILI, data that are easily obtainable in many countries and less subject to bias and subjective interpretation than cause-of-death data. Further work is needed to understand the variations in mortality observed across seasons and in particular the impact of vaccination against influenza.

Burden of illness of the 2009 pandemic of influenza A (H1N1) in Denmark.

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.

[The economic impact of an epidemic of hepatitis A among men who have sex with men]. / Hvad koster et udbrud af hepatitis A blandt maend, der har sex med maend?

INTRODUCTION: In 2004 Denmark had an epidemic of hepatitis A among men who have sex with men (MSM). We estimate the size and the economic impact of the epidemic and discuss possibilities to prevent new epidemics. MATERIALS AND METHODS: The size of the outbreak was estimated from notifications received by the Department of Epidemiology and the number of hepatitis A IgM positive specimens sent to the Department of Virology at Statens Serum Institut. The economical impact was estimated according to data on cost of illness from the National Board of Health and the results of the outbreak investigation. RESULTS: In 2004, 165 cases of hepatitis A in men > 17 years of age were reported compared with a yearly average of 25 cases in the previous 10 years. The size of the outbreak, adjusted for an estimated underreporting of 60% was 220 cases. The economical impact was EUR 650,000, or EUR 3,000 per case. CONCLUSION: Outbreaks of hepatitis A among men who have sex with men are reported from major European cities almost on an annual basis. In the case of an outbreak, we suggest the response should include a targeted information campaign in the MSM media, hygiene control at gay saunas, sex clubs and darkrooms and a free vaccination offer to MSM with frequent partners at locations frequented by MSM. Before an outbreak we propose that vaccination against hepatitis A be recommended to MSM with frequent partners.

Molecular epidemiological studies show that hepatitis A virus is endemic among active homosexual men in Europe.

Large outbreaks of hepatitis A have occurred in Denmark, Germany, the Netherlands, Norway, Spain, Sweden, and the United Kingdom during the period 1997-2005 affecting homosexual men. A collaborative study was undertaken between these countries to determine if the strains involved in these hepatitis A outbreaks were related genetically. The N-terminal region of VP1 and the VP1/P2A region of the strains were sequenced and compared. The majority of the strains found among homosexual men from the different European countries formed a closely related cluster, named MSM1, belonging to genotype IA. Different HAV strains circulated among other risk groups in these countries during the same period, indicating that specific strains were circulating among homosexual men exclusively. Similar strains found among homosexual men from 1997 to 2005 indicate that these HAV strains have been circulating among homosexual men for a long time. The homosexual communities are probably too small within the individual countries to maintain HAV in their population over time, whereas the homosexual communities across Europe are probably sufficiently large to sustain continued circulation of homologous HAV strains for years resulting in an endemic situation among homosexual men.