A study of excess mortality during influenza epidemics in the Czech Republic, 1982–2000

Intensified impacts on mortality due to compound winter extremes in the Czech Republic

Although impacts of extremely cold temperatures on human health have been widely studied, adverse effects of other extreme weather phenomena have so far received much less attention. We employed a high-quality long-term mortality time series (1982-2017) to evaluate impacts of extreme winter weather in the Czech Republic. We aimed to clarify whether compound events of extreme weather cause larger impacts on mortality than do each type of extreme if evaluated individually. Using daily data from the E-OBS and ERA5 datasets, we analyzed 9 types of extreme events: extreme wind gust, precipitation, snowfall, and sudden temperature and pressure changes. Relative mortality deviations from the adjusted baseline were used to estimate the immediate effect of the selected extreme events on excess mortality. The impact was adjusted for the effect of extreme cold. Extreme events associated with sudden rise of minimum temperature and pressure drops had generally significant impact on excess mortality (3.7% and 1.4% increase). The impacts were even more pronounced if these events occurred simultaneously or were compounded with other types of extremes, such as heavy precipitation, snowfall, maximum temperature rise, and their combinations (increase as great as 14.4%). Effects of some compound events were significant even for combinations of extremes having no significant impact on mortality when evaluated separately. On the other hand, a "protective" effect of pressure increases reduced the risk for its compound events. Meteorological patterns during extreme events linked to excess mortality indicate passage of a low-pressure system northerly from the study domain. We identified extreme winter weather events other than cold temperatures with significant impact on excess mortality. Our results suggest that occurrence of compound extreme events strengthen the impacts on mortality and therefore analysis of multiple meteorological parameters is a useful approach in defining adverse weather conditions.

Estimates of global seasonal influenza-associated respiratory mortality: a modelling study

BACKGROUND

Estimates of influenza-associated mortality are important for national and international decision making on public health priorities. Previous estimates of 250 000-500 000 annual influenza deaths are outdated. We updated the estimated number of global annual influenza-associated respiratory deaths using country-specific influenza-associated excess respiratory mortality estimates from 1999-2015.

METHODS

We estimated country-specific influenza-associated respiratory excess mortality rates (EMR) for 33 countries using time series log-linear regression models with vital death records and influenza surveillance data. To extrapolate estimates to countries without data, we divided countries into three analytic divisions for three age groups (<65 years, 65-74 years, and ≥75 years) using WHO Global Health Estimate (GHE) respiratory infection mortality rates. We calculated mortality rate ratios (MRR) to account for differences in risk of influenza death across countries by comparing GHE respiratory infection mortality rates from countries without EMR estimates with those with estimates. To calculate death estimates for individual countries within each age-specific analytic division, we multiplied randomly selected mean annual EMRs by the country's MRR and population. Global 95% credible interval (CrI) estimates were obtained from the posterior distribution of the sum of country-specific estimates to represent the range of possible influenza-associated deaths in a season or year. We calculated influenza-associated deaths for children younger than 5 years for 92 countries with high rates of mortality due to respiratory infection using the same methods.

FINDINGS

EMR-contributing countries represented 57% of the global population. The estimated mean annual influenza-associated respiratory EMR ranged from 0·1 to 6·4 per 100 000 individuals for people younger than 65 years, 2·9 to 44·0 per 100 000 individuals for people aged between 65 and 74 years, and 17·9 to 223·5 per 100 000 for people older than 75 years. We estimated that 291 243-645 832 seasonal influenza-associated respiratory deaths (4·0-8·8 per 100 000 individuals) occur annually. The highest mortality rates were estimated in sub-Saharan Africa (2·8-16·5 per 100 000 individuals), southeast Asia (3·5-9·2 per 100 000 individuals), and among people aged 75 years or older (51·3-99·4 per 100 000 individuals). For 92 countries, we estimated that among children younger than 5 years, 9243-105 690 influenza-associated respiratory deaths occur annually.

INTERPRETATION

These global influenza-associated respiratory mortality estimates are higher than previously reported, suggesting that previous estimates might have underestimated disease burden. The contribution of non-respiratory causes of death to global influenza-associated mortality should be investigated.

FUNDING

None.

Heterogeneity in Estimates of the Impact of Influenza on Population Mortality: A Systematic Review

Influenza viruses are associated with a substantial global burden of morbidity and mortality every year. Estimates of influenza-associated mortality often vary between studies due to differences in study settings, methods, and measurement of outcomes. We reviewed 103 published articles assessing population-based influenza-associated mortality through searches of PubMed and Embase, and we identified considerable variation in the statistical methods used across studies. Studies using regression models with an influenza activity proxy applied 4 approaches to estimate influenza-associated mortality. The estimates increased with age and ranged widely, from -0.3-1.3 and 0.6-8.3 respiratory deaths per 100,000 population for children and adults, respectively, to 4-119 respiratory deaths per 100,000 population for older adults. Meta-regression analysis identified that study design features were associated with the observed variation in estimates. The estimates increased with broader cause-of-death classification and were higher for older adults than for children. The multiplier methods tended to produce lower estimates, while Serfling-type models were associated with higher estimates than other methods. No "average" estimate of excess mortality could reliably be made due to the substantial variability of the estimates, partially attributable to methodological differences in the studies. Standardization of methodology in estimation of influenza-associated mortality would permit improved comparisons in the future.

Estimating the Baseline Incidence of a Seasonal Disease Independently of Epidemic Outbreaks

In epidemiology, it is very important to estimate the baseline incidence of infectious diseases, but the available data are often subject to outliers due to epidemic outbreaks. Consequently, the estimate of the baseline incidence is biased and so is the predicted epidemic threshold which is a crucial reference indicator used to suspect and detect an epidemic outbreak. Another problem is that the "usual" incidence varies in a season dependent manner, i.e. it may not be constant throughout the year, is often periodic, and may also show a trend between years. To take account of these factors, more complicated models adjusted for outliers are used. If not adjusted for outliers, the baseline incidence estimate is biased. As a result, the epidemic threshold can be overestimated and thus can make the detection of an epidemic outbreak more difficult. Classical Serfling's model is based on the sine function with a phase shift and amplitude. Multiple approaches are applied to model the long-term and seasonal trends. Nevertheless, none of them controls for the effect of epidemic outbreaks. The present article deals with the adjustment of the data biased by epidemic outbreaks. Some models adjusted for outliers, i.e. for the effect of epidemic outbreaks, are presented. A possible option is to remove the epidemic weeks from the analysis, but consequently, in some calendar weeks, data will only be available for a small number of years. Furthermore, the detection of an epidemic outbreak by experts (epidemiologists and microbiologists) will be compared with that in various models.

Contrasting patterns of hot spell effects on morbidity and mortality for cardiovascular diseases in the Czech Republic, 1994-2009

The study examines effects of hot spells on cardiovascular disease (CVD) morbidity and mortality in the population of the Czech Republic, with emphasis on differences between ischaemic heart disease (IHD) and cerebrovascular disease (CD) and between morbidity and mortality. Daily data on CVD morbidity (hospital admissions) and mortality over 1994-2009 were obtained from national hospitalization and mortality registers and standardized to account for long-term changes as well as seasonal and weekly cycles. Hot spells were defined as periods of at least two consecutive days with average daily air temperature anomalies above the 95% quantile during June to August. Relative deviations of mortality and morbidity from the baseline were evaluated. Hot spells were associated with excess mortality for all examined cardiovascular causes (CVD, IHD and CD). The increases were more pronounced for CD than IHD mortality in most population groups, mainly in males. In the younger population (0-64 years), however, significant excess mortality was observed for IHD while there was no excess mortality for CD. A short-term displacement effect was found to be much larger for mortality due to CD than IHD. Excess CVD mortality was not accompanied by increases in hospital admissions and below-expected-levels of morbidity prevailed during hot spells, particularly for IHD in the elderly. This suggests that out-of-hospital deaths represent a major part of excess CVD mortality during heat and that for in-hospital excess deaths CVD is a masked comorbid condition rather than the primary diagnosis responsible for hospitalization.

Deaths averted by influenza vaccination in the U.S. during the seasons 2005/06 through 2013/14

BACKGROUND

Excess mortality due to seasonal influenza is substantial, yet quantitative estimates of the benefit of annual vaccination programs on influenza-associated mortality are lacking.

METHODS

We estimated the numbers of deaths averted by vaccination in four age groups (0.5 to 4, 5 to 19, 20 to 64 and ≥65 yrs.) for the nine influenza seasons from 2005/6 through 2013/14. These estimates were obtained using a Monte Carlo approach applied to weekly U.S. age group-specific estimates of influenza-associated excess mortality, monthly vaccination coverage estimates and summary seasonal influenza vaccine effectiveness estimates to obtain estimates of the number of deaths averted by vaccination. The estimates are conservative as they do not include indirect vaccination effects.

RESULTS

From August, 2005 through June, 2014, we estimated that 40,127 (95% confidence interval [CI] 25,694 to 59,210) deaths were averted by influenza vaccination. We found that of all studied seasons the most deaths were averted by influenza vaccination during the 2012/13 season (9398; 95% CI 2,386 to 19,897) and the fewest during the 2009/10 pandemic (222; 95% CI 79 to 347). Of all influenza-associated deaths averted, 88.9% (95% CI 83 to 92.5%) were in people ≥65 yrs. old.

CONCLUSIONS

The estimated number of deaths averted by the US annual influenza vaccination program is considerable, especially among elderly adults and even when vaccine effectiveness is modest, such as in the 2012/13 season. As indirect effects ("herd immunity") of vaccination are ignored, these estimates represent lower bound estimates and are thus conservative given valid excess mortality estimates.

Annual public health and economic benefits of seasonal influenza vaccination: a European estimate

BACKGROUND

Vaccination is currently the most effective means of preventing influenza infection. Yet evidence of vaccine performance, and the impact and value of seasonal influenza vaccination across risk groups and between seasons, continue to generate much discussion. Moreover, vaccination coverage is below recommended levels.

METHODS

A model was generated to assess the annual public health benefits and economic importance of influenza vaccination in 5 WHO recommended vaccination target groups (children 6 - 23 months of age; persons with underlying chronic health conditions; pregnant women; health care workers; and, the elderly, 65 years of age) in 27 countries of the European Union. Model estimations were based on standard calculation methods, conservative assumptions, age-based and country-specific data.

RESULTS

Out of approximately 180 million Europeans for whom influenza vaccination is recommended, only about 80 million persons are vaccinated. Seasonal influenza vaccination currently prevents an annual average of between 1.6 million and 2.1 million cases of influenza, 45,300 to 65,600 hospitalizations, and 25,200 to 37,200 deaths. To reach the 75% vaccination coverage target set by the EU Council Recommendation in 2009, an additional 57.4 million person would need to be vaccinated in the elderly and other risk groups. By achieving the 75% target rate set in EU-27 countries, average annual influenza- related events averted would increase from current levels to an additional +1.6 to +1.7 million cases, +23,800 to +31,400 hospitalization, +9,800 to +14,300 deaths, +678,500 to +767,800 physician visits, and +883,800 to +1,015,100 lost days of work yearly. Influenza-related costs averted because of vaccination would increase by an additional + €190 to + €226 million yearly, in vaccination target groups.

CONCLUSIONS

Full implementation of current influenza vaccination recommendations of 75% vaccination coverage rate (VCR) in Europe by the 2014-2015 influenza season could immediately reduce an important public health and economic burden.

Heat- and cold-stress effects on cardiovascular mortality and morbidity among urban and rural populations in the Czech Republic

Several studies have examined the relationship of high and low air temperatures to cardiovascular mortality in the Czech Republic. Much less is understood about heat-/cold-related cardiovascular morbidity and possible regional differences. This paper compares the effects of warm and cold days on excess mortality and morbidity for cardiovascular diseases (CVDs) in the city of Prague and a rural region of southern Bohemia during 1994-2009. Population size and age structure are similar in the two regions. The results are evaluated for selected population groups (men and women). Excess mortality (number of deaths) and morbidity (number of hospital admissions) were determined as differences between observed and expected daily values, the latter being adjusted for long-term changes, annual and weekly cycles, and epidemics of influenza/acute respiratory infections. Generally higher relative excess CVD mortality on warm days than on cold days was identified in both regions. In contrast to mortality, weak excess CVD morbidity was observed for both warm and cold days. Different responses of individual CVDs to heat versus cold stress may be caused by the different nature of each CVD and different physiological processes induced by heat or cold stress. The slight differences between Prague and southern Bohemia in response to heat versus cold stress suggest the possible influence of environmental and socioeconomic factors such as the effects of urban heat island and exposure to air pollution, lifestyle differences, and divergence in population structure, which may result in differing vulnerability of urban versus rural population to temperature extremes.

Effects of sudden air pressure changes on hospital admissions for cardiovascular diseases in Prague, 1994-2009

Sudden weather changes have long been thought to be associated with negative impacts on human health, but relatively few studies have attempted to quantify these relationships. We use large 6-h changes in atmospheric pressure as a proxy for sudden weather changes and evaluate their association with hospital admissions for cardiovascular diseases (CVD). Winter and summer seasons and positive and negative pressure changes are analysed separately, using data for the city of Prague (population 1.2 million) over a 16-year period (1994-2009). We found that sudden pressure drops in winter are associated with significant rise in hospital admissions. Increased CVD morbidity was observed neither for pressure drops in summer nor pressure increases in any season. Analysis of synoptic weather maps shows that large pressure drops in winter are associated with strong zonal flow and rapidly moving low-pressure systems with centres over northern Europe and atmospheric fronts affecting western and central Europe. Analysis of links between passages of strong atmospheric fronts and hospital admissions, however, shows that the links disappear if weather changes are characterised by frontal passages. Sudden pressure drops in winter are associated also with significant excess CVD mortality. As climate models project strengthening of zonal circulation in winter and increased frequency of windstorms, the negative effects of such weather phenomena and their possible changes in a warmer climate of the twenty-first century need to be better understood, particularly as their importance in inducing excess morbidity and mortality in winter may increase compared to cold spells.

Impacts of hot and cold spells differ for acute and chronic ischaemic heart diseases

Background

Many studies have reported associations between temperature extremes and cardiovascular mortality but little has been understood about differences in the effects on acute and chronic diseases. The present study examines hot and cold spell effects on ischaemic heart disease (IHD) mortality in the Czech Republic during 1994–2009, with emphasis upon differences in the effects on acute myocardial infarction (AMI) and chronic IHD.

Methods

We use analogous definitions for hot and cold spells based on quantiles of daily average temperature anomalies, thus allowing for comparison of results for summer hot spells and winter cold spells. Daily mortality data were standardised to account for the long-term trend and the seasonal and weekly cycles. Periods when the data were affected by epidemics of influenza and other acute respiratory infections were removed from the analysis.

Results

Both hot and cold spells were associated with excess IHD mortality. For hot spells, chronic IHD was responsible for most IHD excess deaths in both male and female populations, and the impacts were much more pronounced in the 65+ years age group. The excess mortality from AMI was much lower compared to chronic IHD mortality during hot spells. For cold spells, by contrast, the relative excess IHD mortality was most pronounced in the younger age group (0–64 years), and we found different pattern for chronic IHD and AMI, with larger effects on AMI.

Conclusions

The findings show that while excess deaths due to IHD during hot spells are mainly of persons with chronic diseases whose health had already been compromised, cardiovascular changes induced by cold stress may result in deaths from acute coronary events rather than chronic IHD, and this effect is important also in the younger population. This suggests that the most vulnerable population groups as well as the most affected cardiovascular diseases differ between hot and cold spells, which needs to be taken into account when designing and implementing preventive actions.

Comparison of UTCI with other thermal indices in the assessment of heat and cold effects on cardiovascular mortality in the Czech Republic

We compare the recently developed Universal Thermal Climate Index (UTCI) with other thermal indices in analysing heat- and cold-related effects on cardiovascular (CVD) mortality in two different (urban and rural) regions in the Czech Republic during the 16-year period from 1994–2009. Excess mortality is represented by the number of deaths above expected daily values, the latter being adjusted for long-term changes, annual and weekly cycles, and epidemics of influenza/acute respiratory infections. Air temperature, UTCI, Apparent Temperature (AT) and Physiologically Equivalent Temperature (PET) are applied to identify days with heat and cold stress. We found similar heat effects on CVD mortality for air temperature and the examined thermal indices. Responses of CVD mortality to cold effects as characterised by different indices were much more varied. Particularly important is the finding that air temperature provides a weak cold effect in comparison with the thermal indices in both regions, so its application—still widespread in epidemiological studies—may underestimate the magnitude of cold-related mortality. These findings are important when possible climate change effects on heat- and cold-related mortality are estimated. AT and PET appear to be more universal predictors of heat- and cold- related mortality than UTCI when both urban and rural environments are of concern. UTCI tends to select windy rather than freezing days in winter, though these show little effect on mortality in the urban population. By contrast, significant cold-related mortality in the rural region if UTCI is used shows potential for UTCI to become a useful tool in cold exposure assessments.

Influenza-related mortality in Spain, 1999-2005

OBJECTIVE

To estimate the excess deaths attributed to influenza in Spain, using age-specific generalized linear models (GLM) and the Serfling model for the period 1999-2005.

METHOD

We reviewed mortality from influenza and pneumonia and all-cause deaths. We used an additive GLM procedure, including the numbers of weekly deaths as a response variable and the number of influenza virus and respiratory syncytial virus weekly isolates, the population and two variables to adjust for annual fluctuations as covariates. Using the Serfling model, we removed the trend and applied a temporal regression model, excluding data from December to April to account for the expected baseline mortality in the absence of influenza activity.

RESULTS

Globally, the excess mortality attributable to influenza was 1.1 deaths per 100,000 for influenza and pneumonia and 11 all-cause deaths per 100,000 using the GLM model. The highest mortality rates were obtained with the Serfling model in adults older than 64 years, with an excess mortality attributable to influenza of 57 and 164 deaths per 100,000 for influenza and pneumonia and all-cause, respectively.

CONCLUSIONS

The GLM model, which takes viral activity into account, yields systematically lower estimates of excess mortality than the Serfling model. The GLM model provides independent estimates associated with the activity of different viruses and even with other factors, which is a significant advantage when trying to understand the impact of viral respiratory infections on mortality in the Spanish population.

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.

Excess mortality from seasonal influenza is negligible below the age of 50 in Israel: implications for vaccine policy

Purpose

Evaluation of the severity of pandemic influenza requires reliable estimates of mortality attributable to the seasonal influenza.

Methods

Excess age-specific mortality during periods of influenza activity was evaluated in Israel during the period 1999–2006 for three death categories. For each respiratory year, the lowest monthly moving average for the mortality rate was subtracted from each month in the period of influenza activity. Average mortality rates in years with minimal influenza activity were deducted from corresponding months to exclude winter mortality unrelated to influenza. The sums of these results were used as estimates of excess mortality rates.

Results

Overall excess mortality rates ranged from 7.7 to 36.1 per 100,000 for all causes, and from 4.4 to 24.4 per 100,000 for respiratory and circulatory causes. Influenza was associated with an average of 869 (range 280–1,516) deaths annually from respiratory and circulatory diseases during seasons with significant influenza activity. About 90% of the influenza-associated mortality from respiratory and circulatory diseases was in the age group 65+ years and about 1% in the age group <50 years. The age group <50 years accounted for an annual average of seven deaths from respiratory and circulatory diseases.

Conclusion

Annual mortality associated with seasonal influenza is highly variable. Under the age of 50 years, there is minimal seasonal influenza associated mortality. This information provides an important baseline for evaluating the severity of the A(H1N1) 2009 influenza pandemic, where persons under 50 years of age were often disproportionately represented.

Excess mortality associated with influenza epidemics in Portugal, 1980 to 2004

Background

Influenza epidemics have a substantial impact on human health, by increasing the mortality from pneumonia and influenza, respiratory and circulatory diseases, and all causes. This paper provides estimates of excess mortality rates associated with influenza virus circulation for 7 causes of death and 8 age groups in Portugal during the period of 1980–2004.

Methodology/Principal Findings

We compiled monthly mortality time series data by age for all-cause mortality, cerebrovascular diseases, ischemic heart diseases, diseases of the respiratory system, chronic respiratory diseases, pneumonia and influenza. We also used a control outcome, deaths from injuries. Age- and cause-specific baseline mortality was modelled by the ARIMA approach; excess deaths attributable to influenza were calculated by subtracting expected deaths from observed deaths during influenza epidemic periods. Influenza was associated with a seasonal average of 24.7 all-cause excess deaths per 100,000 inhabitants, approximately 90% of which were among seniors over 65 yrs. Excess mortality was 3–6 fold higher during seasons dominated by the A(H3N2) subtype than seasons dominated by A(H1N1)/B. High excess mortality impact was also seen in children under the age of four years. Seasonal excess mortality rates from all the studied causes of death were highly correlated with each other (Pearson correlation range, 0.65 to 0.95, P<0.001) and with seasonal rates of influenza-like-illness (ILI) among seniors over 65 years (Pearson correlation rho>0.64, P<0.05). By contrast, there was no correlation with excess mortality from injuries.

Conclusions/Significance

Our excess mortality approach is specific to influenza virus activity and produces influenza-related mortality rates for Portugal that are similar to those published for other countries. Our results indicate that all-cause excess mortality is a robust indicator of influenza burden in Portugal, and could be used to monitor the impact of influenza epidemics in this country. Additional studies are warranted to confirm these findings in other settings.

Relationships between sudden weather changes in summer and mortality in the Czech Republic, 1986-2005

The study examines the relationship between sudden changes in weather conditions in summer, represented by (1) sudden air temperature changes, (2) sudden atmospheric pressure changes, and (3) passages of strong atmospheric fronts; and variations in daily mortality in the population of the Czech Republic. The events are selected from data covering 1986-2005 and compared with the database of daily excess all-cause mortality for the whole population and persons aged 70 years and above. Relative deviations of mortality, i.e., ratios of the excess mortality to the expected number of deaths, were averaged over the selected events for days D-2 (2 days before a change) up to D+7 (7 days after), and their statistical significance was tested by means of the Monte Carlo method. We find that the periods around weather changes are associated with pronounced patterns in mortality: a significant increase in mortality is found after large temperature increases and on days of large pressure drops; a decrease in mortality (partly due to a harvesting effect) occurs after large temperature drops, pressure increases, and passages of strong cold fronts. The relationship to variations in excess mortality is better expressed for sudden air temperature/pressure changes than for passages of atmospheric fronts. The mortality effects are usually more pronounced in the age group 70 years and above. The impacts associated with large negative changes of pressure are statistically independent of the effects of temperature; the corresponding dummy variable is found to be a significant predictor in the ARIMA model for relative deviations of mortality. This suggests that sudden weather changes should be tested also in time series models for predicting excess mortality as they may enhance their performance.

Differences in clinical predictors of influenza in adults and children with influenza-like illness

Influenza contributes significantly to morbidity and mortality in the winter season. The aim of the study was to identify clinical signs and symptoms most predictive of influenza infection in children and adults with influenza-like illness. A prospective systematic sampling analysis of clinical data collected through sentinel surveillance system for influenza in 32 primary care centers and one tertiary care hospital in Slovenia during two consecutive influenza seasons (2004/2005 and 2005/2006) was carried out. Children and adults who had influenza-like illness, defined as febrille illness with sudden onset, prostration and weakness, muscle and joint pain and at least (cough, sore throat, coryza) were included and tested for influenza A and B virus, adenovirus, respiratory syncytial virus and enterovirus by RT-PCR. Clinical data were evaluated in statistical models to identify the best predictors for the confirmation of influenza for children (under age of 15) and adults. Of 1,286 patients with influenza-like symptoms in both seasons 211 were confirmed to have influenza A or B alone and compared to 780 influenza-negative patients. A fever over 38°C, chills, headache, malaise and sore eyes revealed a significant association with positive RT-PCR test for influenza virus in children. In adults, only three symptoms were significantly related to PCR-confirmed influenza infection: fever, cough and abnormal breath sounds. The stepwise logistic regression analysis showed that four symptoms predicted influenza in children: fever (38°C or more) (p=0.010), headache (p=0.030), cough (p=0.044) and absence of abnormal breathing sounds (p=0.015) with sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 5.1%, 98.1%, 57.1% and 80.1%, respectively. For adults, the strongest impact on influenza positivity was found for fever (p=0.008) and cough (p=0.085). The model for adults had less favorable characteristics, with sensitivity, specificity, PPV and NPV of 0%, 100%, 0% and 76.4%, respectively. Differences in clinical predictors of influenza in children compared to adults were found. The model for adults was acceptable but not a good one. The model for children was found to be more reliable than the prediction model for adults.

Confounding by season in ecologic studies of seasonal exposures and outcomes: examples from estimates of mortality due to influenza

PURPOSE

Many health outcomes exhibit seasonal variation in incidence, including accidents, suicides, and infections. For seasonal outcomes it can be difficult to distinguish the causal roles played by factors that also vary seasonally, such as weather, air pollution, and pathogen circulation.

METHODS

Various approaches to estimating the association between a seasonal exposure and a seasonal outcome in ecologic studies are reviewed, using studies of influenza-related mortality as an example. Because mortality rates vary seasonally and circulation of other respiratory viruses peaks during influenza season, it is a challenge to estimate which winter deaths were caused by influenza. Results of studies that estimated the contribution of influenza to all-cause mortality using different methods on the same data are compared.

RESULTS

Methods for estimating associations between season exposures and outcomes vary greatly in their advantages, disadvantages, and assumptions. Even when applied to identical data, different methods can give greatly different results for the expected contribution of influenza to all-cause mortality.

CONCLUSIONS

When the association between exposures and outcomes that vary seasonally is estimated, models must be selected carefully, keeping in mind the assumptions inherent in each model.

Excess cardiovascular mortality associated with cold spells in the Czech Republic

Background

The association between cardiovascular mortality and winter cold spells was evaluated in the population of the Czech Republic over 21-yr period 1986–2006. No comprehensive study on cold-related mortality in central Europe has been carried out despite the fact that cold air invasions are more frequent and severe in this region than in western and southern Europe.

Methods

Cold spells were defined as periods of days on which air temperature does not exceed -3.5°C. Days on which mortality was affected by epidemics of influenza/acute respiratory infections were identified and omitted from the analysis. Excess cardiovascular mortality was determined after the long-term changes and the seasonal cycle in mortality had been removed. Excess mortality during and after cold spells was examined in individual age groups and genders.

Results

Cold spells were associated with positive mean excess cardiovascular mortality in all age groups (25–59, 60–69, 70–79 and 80+ years) and in both men and women. The relative mortality effects were most pronounced and most direct in middle-aged men (25–59 years), which contrasts with majority of studies on cold-related mortality in other regions. The estimated excess mortality during the severe cold spells in January 1987 (+274 cardiovascular deaths) is comparable to that attributed to the most severe heat wave in this region in 1994.

Conclusion

The results show that cold stress has a considerable impact on mortality in central Europe, representing a public health threat of an importance similar to heat waves. The elevated mortality risks in men aged 25–59 years may be related to occupational exposure of large numbers of men working outdoors in winter. Early warnings and preventive measures based on weather forecast and targeted on the susceptible parts of the population may help mitigate the effects of cold spells and save lives.

Decreased impacts of the 2003 heat waves on mortality in the Czech Republic: an improved response?

The paper examines impacts on mortality of heat waves in 2003, the hottest summer on record in the Czech Republic, and compares them with previous similar events. While most summer heat waves over the period since 1986 were associated with significantly elevated mortality, this was not the case for three out of the four heat waves in 2003. The relatively weak mortality response was particularly noteworthy for the most severe heat wave which occurred in the first 10 days of August 2003 and resulted in enormous excess mortality in some western European countries. A mortality displacement effect and short-term adaptation to heat contributed to the reduced mortality impacts of the heat waves that followed after previous relatively warm periods. However, the decreased mortality response of the 2003 heat waves compared to previous heat waves in the 1990s is also likely to have arisen from positive health-care and other socio-economic changes in the post-communist central European region over the past decade, as well as a better public awareness of heat-related risks due to enhanced media coverage and regular biometeorological forecast and warnings.

Trends for influenza-related deaths during pandemic and epidemic seasons, Italy, 1969-2001

During epidemics, excess deaths were similar in amplitude and time across 3 regions.

Age-specific patterns of death from influenza vary, depending on whether the influenza season is epidemic or pandemic. We assessed age patterns and geographic trends in monthly influenza-related deaths in Italy from 1969 through 2001, focusing on differences between epidemic and pandemic seasons. We evaluated age-standardized excess deaths from pneumonia and influenza and from all causes, using a modified version of a cyclical Serfling model. Excess deaths were highest for elderly persons in all seasons except the influenza A (H3N2) pandemic season (1969–70), when rates were greater for younger persons, confirming a shift toward death of younger persons during pandemic seasons. When comparing northern, central, and southern Italy, we found a high level of synchrony in the amplitude of peaks of influenza-related deaths.

Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918-20 pandemic: a quantitative analysis

BACKGROUND

The threat of an avian influenza pandemic is causing widespread public concern and health policy response, especially in high-income countries. Our aim was to use high-quality vital registration data gathered during the 1918-20 pandemic to estimate global mortality should such a pandemic occur today.

METHODS

We identified all countries with high-quality vital registration data for the 1918-20 pandemic and used these data to calculate excess mortality. We developed ordinary least squares regression models that related excess mortality to per-head income and absolute latitude and used these models to estimate mortality had there been an influenza pandemic in 2004.

FINDINGS

Excess mortality data show that, even in 1918-20, population mortality varied over 30-fold across countries. Per-head income explained a large fraction of this variation in mortality. Extrapolation of 1918-20 mortality rates to the worldwide population of 2004 indicates that an estimated 62 million people (10th-90th percentile range 51 million-81 million) would be killed by a similar influenza pandemic; 96% (95% CI 95-98) of these deaths would occur in the developing world. If this mortality were concentrated in a single year, it would increase global mortality by 114%.

INTERPRETATION

This analysis of the empirical record of the 1918-20 pandemic provides a plausible upper bound on pandemic mortality. Most deaths will occur in poor countries--ie, in societies whose scarce health resources are already stretched by existing health priorities.