Uniform definition of asthma severity, control, and exacerbations: Document presented for the World Health Organization Consultation on Severe Asthma.

Asthma is a global health problem affecting around 300 millionindividuals of all ages, ethnic groups and countries. It isestimated that around 250,000 people die prematurely each yearas a result of asthma. Concepts of asthma severity and controlare important in evaluating patients and their response totreatment, as well as for public health, registries, and research(clinical trials, epidemiologic, genetic, and mechanistic studies),but the terminology applied is not standardized, and terms areoften used interchangeably. A common international approach isfavored to define severe asthma, uncontrolled asthma, and whenthe 2 coincide, although adaptation may be required inaccordance with local conditions. AWorld Health Organizationmeeting was convened April 5-6, 2009, to propose a uniformdefinition of severe asthma. An article was written by a group ofexperts and reviewed by the Global Alliance against ChronicRespiratory Diseases review group. Severe asthma is defined bythe level of current clinical control and risks as ‘‘Uncontrolledasthma which can result in risk of frequent severe exacerbations(or death) and/or adverse reactions to medications and/orchronic morbidity (including impaired lung function or reducedlung growth in children).’’ Severe asthma includes 3 groups, eachcarrying different public health messages and challenges: (1)untreated severe asthma, (2) difficult-to-treat severe asthma, and(3) treatment-resistant severe asthma. The last group includesasthma for which control is not achieved despite the highest levelof recommended treatment and asthma for which control can bemaintained only with the highest level of recommendedtreatment.