Asthma does not have to be a burden or cause suffering.

The Global Asthma Report 2014

Age-standardised asthma mortality rates for all ages 2001-2010 from countries where asthma is separately coded as a cause of death, ordered by mortality rate and country income group.

Figure 1: Age-standardised asthma mortality rates for all ages 2001-2010 from countries where asthma is separately coded as a cause of death, ordered by mortality rate and country income group.

Age-standardised asthma mortality rates for ages 5-34 years only, 2001-2010 from countries where asthma is separately coded as a cause of death, ordered by mortality rate and country income group.

Figure 2: Age-standardised asthma mortality rates for ages 5-34 years only, 2001-2010 from countries where asthma is separately coded as a cause of death, ordered by mortality rate and country income group.

Age-standardised asthma mortality rates and age-standardised hospital admission rates for asthma, in European countries providing recent data for both (2001-2010).

Figure 3: Age-standardised asthma mortality rates and age-standardised hospital admission rates for asthma, in European countries providing recent data for both (2001-2010).

Avoidable asthma deaths are still occurring due to inappropriate management of asthma, including over-reliance on reliever medication rather than preventer medication.

ASTHMA MORTALITY

Deaths due to asthma are uncommon but are of serious concern because many of them are preventable. Most deaths certified as caused by asthma occur in older adults, although comparisons of mortality rates have tended to focus upon children and younger adults. Over the past 50 years, mortality rates in these younger age groups have fluctuated markedly in several high-income countries, attributed to changes in medical care for asthma, especially the introduction of new asthma medications.

International comparisons

Asthma is a rare cause of mortality, contributing to less than 1% of all deaths in most countries worldwide. Rates of death from asthma rise almost exponentially from mid-childhood to old age, so the majority of asthma deaths occur after middle age. However, there is considerable potential for diagnostic confusion with other forms of chronic respiratory disease in the older age groups, so comparisons of mortality rates have tended to focus on children and younger adults.

International mortality statistics for asthma are limited to those countries reporting a full set of causes of death. Figure 1 compares the mortality rates (age-standardised) for asthma among countries reporting asthma separately in recent years (around 2010). For some of the less populous countries with few asthma deaths, there is a substantial range of uncertainty around the published rate. However, among the more populous countries there is a 100-fold variation in age-adjusted rates, for instance between the Netherlands (low) and South Africa (high).

When the comparisons are limited to 5-34 year olds (Figure 2), numbers of deaths are fewer and margins of error are larger, but the disparities persist.

Trends over time

The Global Burden of Disease Study (GBD) Study estimates that age-standardised death rates from asthma fell by about one-third between 1990 and 2010: from 250 per million to 170 per million among males, and from 130 per million to 90 per million among females. These worldwide figures include all ages.

More detailed comparisons have been made over a longer time period in high-income countries, focussing on younger age groups. Over the past half-century, there have been two distinct peaks in asthma mortality in a number of high-income countries (Hospital Admissions, Figure 3).

The first, during the mid-to-late 1960s, represented an approximately 50% increase in asthma death rates among 5-34 year olds. It is generally attributed to the introduction of high-dose isoprenaline inhalers as an asthma reliever medication, which can have toxic effects on the heart during acute asthma attacks. When these medications were withdrawn, the 1960s epidemic of asthma deaths subsided.

The second epidemic, during the mid-1980s, represented an increase of approximately 38% in asthma death rates among 5-34 year olds. In at least some of the affected countries, it was probably due to the widespread use of fenoterol, another inhaled asthma medication with potential cardiac toxicity. However, this second epidemic was also observed in some countries, such as the United States of America, where fenoterol was never approved or widely used.

Relationship of mortality to other measures of the burden of asthma

Taking a 50-year perspective, the epidemics of asthma mortality (related to the use of older asthma relievers with potentially toxic side effects) understandably bear little relationship to the time trends for asthma prevalence or hospital admission rates for asthma. In several high-income countries, asthma admission rates among children rose to a peak in the 1990s, after the 1980s peak in asthma mortality. However, both hospital admission rates and asthma mortality rates among children have been declining since 2000 in countries where they have been measured, whereas asthma prevalence has been stable or rising in many countries (Hospital Admissions, Figure 3).

When national asthma mortality rates for children were compared with the asthma symptoms prevalence and severity data for the International Study of Asthma and Allergies in Childhood (ISAAC) Phase One centres in the same countries, a significantly positive correlation was found between childhood asthma mortality and the prevalence of more severe asthma symptoms in both 6-7 year olds (29 countries) and 13-14 year olds (38 countries).

Such comparisons need to be interpreted with caution, because ISAAC centres are not necessarily representative of the countries in which they are located. However, when comparing mortality and hospital admission rates, national data can be used in both instances. Figure 3 shows this comparison for 24 European countries which have reported recent data for both outcomes. There is a significantly positive correlation between mortality and admission rates for asthma at all ages.

Avoidable factors in asthma deaths

Although asthma mortality rates have declined in many high-income countries, confidential enquiries in the United Kingdom have suggested that avoidable factors still play a part in the majority of asthma deaths.

The most recent comprehensive review, of 195 asthma deaths in the United Kingdom during 2012-2013, found that nearly half died without seeking medical assistance or before emergency medical care could be provided, and the majority were not under specialist medical supervision during the year prior to death. Only one-quarter had been provided with a personal asthma action plan, acknowledged to improve asthma care, and there was evidence of excessive prescribing of short-acting reliever medication, under-prescribing of preventer medication, and inappropriate prescribing of long-acting beta-agonist bronchodilator inhalers as the sole form of treatment.

These observations, from a high-income country with a tradition of evidence-based medicine and a national health service which is free at the point of use, suggest that improved access to appropriate asthma medication is a key goal in reducing asthma mortality worldwide.

Conclusion

Asthma deaths represent the “tip of the iceberg” with respect to the global burden of asthma. Although the risk of any individual asthmatic patient dying of their disease is thankfully very low, continued surveillance of asthma mortality rates is essential to monitor progress in asthma care, and as an early warning of epidemics of fatal asthma, as have occurred in the past half-century.

Recommendation

Health authorities in all countries should report rates of asthma deaths in children and adults to monitor progress in asthma care and as an early warning of epidemics of fatal asthma.

David Strachan, Elizabeth Limb, Neil Pearce, Guy Marks

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