Research worldwide has documented poor adherence to treatments for asthma although there are large variations between countries (33). Rates of nonadherence among patients with asthma range from 30% to 70%, whether adherence is measured as percentage of prescribed medication taken, serum theophylline levels, days of medication adherence, or percentage of patients who failed to reach a clinically estimated adherence minimum (34). Evidence shows that adherence rates for the regular taking of preventive therapies are as low as 28% in developed countries (35,36).

Adherence is also a serious problem in particular populations such as children and adolescents. In adolescents, adherence to prescribed pulmonary medication may be as low as 30% in general practice (37). The complexity of optimum routine management of the disease - almost one hundred per cent self-managed - results in reduced adherence (38).

Failure to adhere to a regular self-management plan for asthma (including the regular taking of preventive therapies) results in poor asthma control which has clinical consequences, such as exacerbation of asthma, and decreased quality of life for the patients, as well as economic consequences, such as increased hospitalization and emergency department visits, resulting in unnecessarily high costs of health care.

There is a large variation between countries in the costs associated with asthma, but there are several outstanding commonalities: the total cost of asthma as a single condition currently comprises up to 1 to 2% of health care expenditures; hospitalization and emergency care are consistently, disproportionately high, and there is a nearly 1: 1 relationship between direct and indirect costs. The available data suggest that this distribution of excess costs is attributable to nonscheduled acute or emergency care, indicating poor asthma management and control (39). Such data highlight the significant cost of hospital care for asthma, compared to the costs of the more frequently used and less costly outpatient and pharmaceutical services.

Economic studies consistently show that the costs incurred by an adult with poorly controlled asthma are higher than those for a well-controlled patient with the same severity of disease. For severe asthma, it has been estimated that the savings produced by optimal control would be around 45% of the total medical costs (39). Poorer adherence to medication among elderly patients with moderate-to-severe asthma was associated with a 5% increase in annual physician visits, whereas better adherence was associated with a 20% decrease in annual hospitalization (40). This represents a significant potential cost saving to society in addition to the improvement in the quality of life and productive output of the affected individuals.

To the individual with asthma, or his or her family, the costs of asthma can be immense. For example, studies have demonstrated that the average amount spent by a family on medical treatments for children with asthma in the United States ranged between 5.5 and 14.5% of family income (41). In India, a study in the state of Andhra Pradesh estimated that the average expenditure for asthma treatment was about 9% of per capita income (42).

The above discussion shows that when asthma is not well controlled, it is likely to affect the social functioning of a country, impairing not only child development and education but also causing disruption in job training or ongoing employment for millions of adults worldwide.