Prevalence and incidence, and changing patterns of asthma with age
The prevalence of childhood asthma increased markedly in Europe in the second half of the 20th century. This is exemplified by published studies of asthma in schoolchildren in Norway, which have reported an increase in prevalence from 0.4% in 1948 to 12.3% in the mid-1990s and 20% in a study performed in 2004, although the most recent study, in 2008, reported a levelling off to 17.6% (figure 1). The increase was initially most marked in western Europe. The questionnaires developed for the International Study of Asthma and Allergy in Childhood (ISAAC) have provided a common tool for assessing the prevalence of asthma and wheezing disorders in children. In the ISAAC study performed in 1997, the highest prevalence of childhood asthma in Europe was found in the British Isles, with the prevalence of ‘asthma ever’ (lifetime prevalence of asthma) ranging from 1.6% in Albania to 20.7% in the UK for 13–14-year-old children, and from 1.4% in Estonia to 22.9% in the UK among 6–7-year-olds, with markedly increasing rates across Europe from East to West (figure 2). This East-to-West difference has diminished over recent years with a relative increase in lifetime prevalence in eastern Europe compared with the West; this may be related to simultaneous changes in lifestyle in eastern Europe. Figure 3 shows the prevalence rates of current wheezing in the ISAAC study phase III (data collected 2002–2003) in various centres in Europe.
The prevalence, causes and clinical presentation of asthma all vary with age. Many children first develop symptoms during infancy, but many cease wheezing in early childhood. Asthma can appear de novo throughout life, but it starts most commonly in early childhood, as illustrated in figure 4. This Canadian study reported that asthma affected approximately one-third of the population at some time between the ages of 4 and 80 years, much like diabetes or malignant disease. However, asthma starts much earlier in life than other disorders and thus has a lifelong impact on quality of life and health costs. The economic consequences of asthma are therefore particularly high due to its frequent early onset.
Asthma mortality in children is low and over recent years it has decreased in most European countries. Historically, mortality was highest among the youngest children, lower during school age, and then increased from puberty to adulthood.
In Denmark, a significant upward trend in asthma mortality was seen between 1973 and 1987. This was due solely to increasing mortality in the 15–19-year-old age group. From 1988 to 1994, the mortality rate among children aged less than 19 years decreased in general. In Norway, mortality among children ≥5 years of age has been consistently low since 1960, while in children <5 years of age the mortality rate decreased until 1990 and was then as low as in the older age-groups. In contrast, in Russia an increasing mortality rate among children <5 years of age was reported, from 0.06 per 100 000 in 1980 to 0.11 per 100 000 in 1989; there was, however, no increase among 5–34-year-old asthmatic subjects.
In the Netherlands, asthma mortality declined among 5–34-year-olds between 1980 and 1994, remaining stable among other age groups, whereas in England there was no change in asthma mortality among children aged 0–14 years from 1980 (0.389 per 100 000) to 1990 (0.387 per 100 000) compared to a 24% reduction in mortality for all causes. A further reduction in asthma mortality was seen in five European countries (France, Germany, Italy, Spain and the UK) between 1994 and 2005 among children and young adults (aged 5–34 years). Nevertheless, in 2004, there still remained 6700 possibly preventable deaths at all ages in these five countries.
In Sweden, the rate of asthma deaths among children and young adults (aged 1–34 years) decreased between 1994 and 2003. It was, however, remarkable that nine of the 12 deaths in the population aged <19 years were due to anaphylaxis, with asthma caused by food allergy.
When comparing childhood asthma mortality between countries, there are noteworthy correlations between the prevalence of asthma symptoms and asthma mortality as well as hospital admissions for asthma. Any reduction in prevalence may therefore have an impact upon asthma mortality. The decreasing mortality rate of asthma during childhood seen in most countries over the past two decades is probably due to the more widespread use of inhaled corticosteroids (which, even in low doses, have been shown to decrease mortality), together with improved treatment of acute asthma attacks.
Recent data (2004–2010, from the World Health Organization (WHO)) for children aged 0–14 years show that mortality is generally very low in Europe, with little difference between countries, implying better control of the condition with improvements in treatment.
Asthma morbidity is a major burden for the child, his/her family and the community. Asthma attacks are very frightening for the child and due to the resulting disruption of life and reduced physical ability there is an emotional, as well as economic, impact of the disease. The social burden of asthma is considerable, not only on the sick child but also on parents, siblings and the household in general. In England, 69% of parents or partners of parents of asthmatic children reported taking time off from work because of the child’s asthma, while 13% had given up their jobs completely. In assessing quality of life in asthmatic children, it is important also to assess the quality of life of the caregivers.
Severe problematic asthma that is poorly responsive to the common asthma treatments has been reported in approximately 4.5% of children with current asthma.
Direct healthcare costs for childhood asthma arise from consultations in both primary and secondary care, as well as hospital admissions (figure 5) and treatment costs. In some, but not all, countries, hospital admissions have fallen in recent years (see above), but greater use of both inhaled and oral agents has increased the expenditure on asthma drugs. A number of new drugs have recently been introduced, thereby increasing the drug-related cost. In particular, the use of inhaled steroids has increased markedly in recent years.
Although loss of working days is not directly applicable to children, absence from school is a comparable consequence. Good European studies are difficult to find, but one US study reported 10.1 million days’ absence from schools due to asthma in 1 year, extrapolated from a study of 17 000 families.