Allergic diseases are major public health problem in many industrialized countries¹. Over the last three decades allergic diseases (including asthma) have significantly increased and the trend continues upwards. The increase has been noted both for children and adults across all social classes.

The International Study of Asthma and Allergies in childhood (ISAAC)^2,3 and the European Community Respiratory Health Survey (ECRHS)⁴ in adults have produced an extensive amount of data on the prevalence of asthma and allergic rhinitis worldwide. 

a) International rates

On a total of 721.601 children worldwide, from 1.4 % to 28.9 % suffered from rhinitis symptoms. Regarding asthma, these numbers ranged between 1.6 to 36.8 % and, when considering atopic dermatitis, the rates ranged between 0.3 % and 20.5 %.

In Europe, 65 % of the adults with allergy have allergic rhinitis, 27 % have asthma, 22 % have skin allergy and 13 % have food allergy. One child on 4 is allergic in Europe. Considering the adults, prevalence rates of asthma range from 5 % to 10 %. From 1 to 15 % of European children are asthmatic. The National Health Interview Survey (NHIS), a population-based interview survey in USA, reported in 1996, that 5.5 % of US residents or almost 14.5 million people have asthma⁵. 

b) A substantial variation across countries 

Both ISAAC and ECRHS showed a substantial variation within and between countries. Positive skin prick tests are more common in children living in urban regions versus the-ones living in rural areas⁶. There is a substantial variation by region and across countries in asthma mortality rates. 

The ECHRS assessed geographic variation in asthma in 140.000 adults from 22 countries. A high prevalence of asthma (> 7%) was found in Australia, New Zealand, USA, Ireland and UK while a low prevalence (< 4 %) was found in Iceland, Germany, Italy, Algeria and India. 

c) The prevalence is rising

Accurate records on the prevalence of allergic rhinitis are lacking before the 20th century. However, interesting data can be found in some national archives. In Switzerland, the prevalence of self-reported current hay-fever (the common name to designate seasonal allergic rhinitis) was found to be 0.82% in 1926. In 1958, this prevalence rose to 4.8%. In 1985, an increase to 9.6% is noticed. In 1995, a further rise of self-reported current hay fever to 14.2% was demonstrated^7,8. 

In USA, the prevalence of allergic rhinitis in 1996 has increased of 66 % from 1970. Similar results can also be found in other countries. A doubling of the prevalence of seasonal allergic rhinitis between 1971 and 1981 was noticed in Sweden among army recruits (4.4% versus 8.4%)⁹. Serial studies in Aberdeen schoolchildren (Scotland) indicated an increase in prevalence of allergic rhinitis between 1964 and 1989 from 3.2% to 11.9%. In Italy, a significant increase from 15.4% to 18.3% was observed for the prevalence of allergic rhinitis¹⁰.

Epidemiologic data have provided substantial insights into the patterns of occurrence of asthma and the factors that determine risks for the disease. The age-dependent incidence of asthma and its natural history have been particularly described. The important variation in frequency of asthma has been clearly demonstrated from comparisons of urban, suburban and rural environments. But the major information learned from epidemiologic surveys is the significant rise of the prevalence of asthma in many developed countries. For example, nowadays, nearly 80 million patients are suffering from asthma in Europe. In USA, the prevalence rate for asthma increased by 55 % for whites and 77.5% for blacks from 1982 to 1996¹¹. Changes in the prevalence of asthma have been associated with changes in prevalence of sensitization, and these could explain part of the increase in the prevalence of asthma during the 1990's¹². Recently, in an Italian epidemiological survey, the authors found that the prevalence of asthma attacks did not vary significantly from 1991 to 1993 (3.6%) to 1998 to 2000 (3.2%). However, the asthma-like symptoms tended to increase in the youngest age class (20 to 26 years)¹⁴.

Although death due to asthma is relatively rare, mortality rates serve as indicators of the impact of the disease on the population, the consequent management and the efficacy of health politics. In the world, nearly 180.000 deaths by asthma are annually reported worldwide. From 1965 to 1977, in United States, a marked decline was observed, but from 1978 to 1989, asthma mortality nearly doubled ¹³. However, it seems that this increase of asthma mortality can be attributed to the increasing asthma prevalence. Like in USA, prevalence of asthma mortality is rising in some European countries. However, asthma mortality rates are not widely available for many countries, particularly the less developed nations. Analyses of recent trends indicate an increase in asthma mortality rates ¹⁴.

There is an important relationship between allergic diseases and indoor our outdoor pollution. Significant higher prevalence of atopy and allergic asthma was observed in the early 1990s among populations living in western compared with eastern European countries ¹⁵. Interestingly, areas of low prevalence of asthma and atopic conditions have recently been identified in developing countries and in Eastern Europe. In Eastern Germany where drastic changes towards westernization of living conditions have occurred after reunification an increase in the prevalence of hay fever and atopic sensitization has been documented over the last 4-5 years in children aged between 9 and 10 years of age (16,17,18). The prevalence in women is 47% and in men 33%. Extremely high allergy rates were found among West German women at the age of 30-39 years (62%). Although the frequency of allergies decreases with increasing age, considerably high morbidity rates were ascertained even in the oldest age groups. The prevalence in participants aged 70-79 years amounts to 25%. Clear differences between East and West could be demonstrated in this age group, too (West 27% and East 14%) ¹⁹. The increase in eczema, rhinitis and asthma is likely to be related to an increase in atopy since seasonal allergic rhinitis is a pure allergic condition and eczema and asthma are also largely allergic in origin ⁷. Social advantages and low birth order appear to be the independently consistent determinants of atopic diseases. Maternal smoking is an additional risk factor for wheeze, which applies primarily in low socioeconomic groups ²⁰. Finally, a number of risk factors have been identified for the development of asthma, such as indoor allergens, tobacco smoke exposure. The gene-environment interaction is actually the leading concept of asthma pathogenesis.

All these epidemiologic data provide evidence for an increase in allergic diseases namely an increased symptom occurrence, mortality, health service utilization. Furthermore, these data find explanations for the high geographical variations and the ethnic differences. Finally, they promote new hypotheses for the natural history, the interference between genes and environment leading to the development of allergy and asthma.