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

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Asthma is a global health problem affecting around 300 million individuals of all ages, ethnic groups and countries. It is estimated that around 250,000 people die prematurely each year as a result of asthma. Concepts of asthma severity and control are important in evaluating patients and their response to treatment, 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 are often used interchangeably. A common international approach is favored to define severe asthma, uncontrolled asthma, and when the 2 coincide, although adaptation may be required in accordance with local conditions. A World Health Organization meeting was convened April 5-6, 2009, to propose a uniform definition of severe asthma. An article was written by a group of experts and reviewed by the Global Alliance against Chronic Respiratory Diseases review group. Severe asthma is defined by the level of current clinical control and risks as “Uncontrolled asthma which can result in risk of frequent severe exacerbations (or death) and/or adverse reactions to medications and/or chronic morbidity (including impaired lung function or reduced lung growth in children).” Severe asthma includes 3 groups, each carrying 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 includes asthma for which control is not achieved despite the highest level of recommended treatment and asthma for which control can be maintained only with the highest level of recommended treatment.

Section snippets

Goal of the WHO consultation

The goal of the WHO Consultation on Severe Asthma (Geneva, April 6-7, 2009) was to propose a WHO definition of asthma severity and control as well as criteria for describing exacerbations and their severity, which should be applicable in most circumstances in low-, middle-, and high-income countries.

Diversity of asthma management across the world

The management of asthma differs widely and is dependent on patients' centered problems (socioeconomic and cultural barriers) as well as national, economic, and health provider settings. In high-income countries, most antiasthma treatments are available and, for the majority of patients, are affordable. Therefore, asthma management in these countries is possible using guidelines formulated without respect to medication availability, cost, and affordability. However, in many LMICs, essential

Components of asthma severity

The concepts of asthma severity, control, and responsiveness are linked.20, 21 Asthma severity is the intrinsic severity of the disease process, asthma control is the degree to which therapy goals are met, and responsiveness is the ease with which asthma control is achieved by therapy. The definition of asthma severity includes all these components, as depicted in Table II.

Uniform definition of severe asthma

Severe asthma is defined by the level of current clinical control and risks as “Uncontrolled asthma which can result in risk of frequent severe exacerbations (or death) and/or adverse reactions to medications and/or chronic morbidity (including impaired lung function or reduced lung growth in children).”

Severe asthma includes 3 groups, each carrying different public health messages and challenges:

  • 1.

    Untreated severe asthma.

  • 2.

    Difficult-to-treat severe asthma.

  • 3.

    Treatment-resistant severe asthma. This

Subphenotyping of severe/uncontrolled asthma

Asthma is a complex, multidimensional disease with marked heterogeneity. Tools to phenotype individual asthma subtypes are now being developed to characterize the various patterns of triggers that induce symptoms, different clinical presentations of the disease, and different inflammatory markers (Fig 2). Phenotyping subtypes can be used to characterize and predict disease severity, progression, and response to treatment and may help identify targets for treatment. Heterogeneity also exists

Asthma and wheezing in children

Childhood asthma represents a serious problem worldwide with increasing trends in LMICs.84 In childhood asthma, specific factors need to be considered including environmental factors (eg, sensitization to allergens, early-age smoking and environmental tobacco smoke, early-life infections, food allergy), correct use of medications (eg, spacers) and fear of ICS. Moreover, asthma severity in children may be very different from that in adults (eg, baseline airway caliber often normal, highly

Public health

For public health purposes, a uniform definition of severe asthma is needed to identify those patients who require particular attention, to ensure appropriate treatment and regular monitoring, and to improve adherence to treatment to reduce the use of emergency departments and hospitalizations. The aim is to optimize health care planning and policies. This definition will also contribute to accurate estimates of the prevalence of severe asthma and provide support for more precise calculations

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  • Cited by (0)

    In collaboration with the Global Allergy and Asthma European Network (GA2LEN), supported by the Sixth EU Framework program for research (contract no. FOOD-CT-2004-506378) and the World Health Organization Collaborating Center on Asthma and Rhinitis, Montpellier.

    Disclosure of potential conflict of interest: J. Bousquet has received honorarium for scientific and advisory boards, lectures, and press conferences from Stallergenes, Actelion, Almirall, AstraZeneca, Chiesi, Ask, Merck, MSD, Novartis, OM Pharma, Sanofi-Aventis, Schering-Plough, Teva, and Uriach. A. A. Cruz has given talks for Novartis and GlaxoSmithKline; has received research support from Chiesi, Mantecorp (Brazil), CNPq (Brazil), National Research Council, Brazilian Ministry of Health, FAPESB State of Brazil Agency for Research, Wellcome Trust (UK), Novartis, and GlaxoSmithKline; is a member of the Planning Group for the Global Alliance against Chronic Respiratory Diseases; and is a member of the Executive Committee for the Global Initiative for Asthma and Allergic Rhinitis and its Impact on Asthma. E. R. Bleecker is a consultant for Aerovance, AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, and Pfizer and has received research support from the NIH/NHLBI. C. E. Brightling is a consultant for MedImmune, AstraZeneca, and Roche and has received research support from MedImmune, AstraZeneca, and GlaxoSmithKline. P. Burney has received research support from the Department of Health (UK). W. W. Busse is on the Advisory Board for Altair, Amgen, Centocor, GlaxoSmithKline, Merck, Pfizer, Wyeth, and Johnson & Johnson; is a consultant for AstraZeneca, Boehringer Ingelheim, Novartis, TEVA, and GlaxoSmithKline; is a speaker for Merck; and has received research support from NIH-NIAID, NIH-NHLBI, Novartis, AstraZeneca, GlaxoSmithKline, MedImmune, and Ception. T. B. Casale is executive vice president of the AAAAI and is on the board of directors for WAO. R. Chen is a consultant on asthma and COPD for AstraZeneca and GlaxoSmithKline and has served as an expert witness on the topic of management of asthma. K. F. Chung is a consultant for Gilead; is on the advisory board for Merck and GlaxoSmithKline; and has received research support from MRC UK, Asthma UK, and Wellcome Trust. R. Dahl is a speaker for MSD, AstraZeneca, ALK, and GlaxoSmithKline; is a speaker and is on the advisory board for TEVA, Boehringer Ingelheim, UCB, Airsonett, Novartis, and Pfizer; is chairman for the Danish Respiratory Society; and is president of Interasma. L. M. Fabbri is a consultant for Nycomed, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, Sigma Tau, AstraZeneca, Merck Sharp & Dohme, Novartis, Roche, and Pfizer; has received paid lecture fees from Abbott, AstraZeneca, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, Merck Sharp & Dohme, Novartis, Nycomed, Roche, and Pfizer; and has received research support from Nycomed, Abbott, AstraZeneca, Boehringer Ingelheim, Menarini, Novartis, Schering-Plough, Chiesi, GlaxoSmithKline, Merck Sharp & Dohme, UCB, Pfizer, the Italian Ministry of Health, and the Italian Ministry for University and Research. S. T. Holgate is a consultant for MSD, Novartis, Synergen, Altair, Amgen, and Almiral and owns shares in Synergen. T. Haahtela has received honoraria from Astellas, AstraZeneca, Leiras, MSD, and Orion Pharma. P. O'Byrne is on the advisory board and has received speakers' honoraria from AstraZeneca and GlaxoSmithKline; is on the advisory board for Topigen, Wyeth, and Schering; and has received research support from AstraZeneca, GlaxoSmithKline, Merck, Wyeth, Schering, and Alexion. K. F. Rabe has received remuneration from Nycomed, Forest, AZ, BI, Chiesi, Pearl, MSD, and GlaxoSmithKline and has received research support from Chiesi, AS, BI, and Novartis. C. van Weel has received research support from Boehringer Ingelheim, GlaxoSmithKline, Novartis, the Dutch Asthma Foundation (NAF), and the Netherlands Medical Research Council (Zon/Mw). S. Wenzel is a consultant for Altair, Merck, GlaxoSmithKline, Amgen, and Pearl Therapeutics; is on the scientific advisory board for Amira; and has received research support from MedImmune, GlaxoSmithKline, Aerovance, and Amgen. T. Zuberbier is a consultant for Schering-Plough, Novartis, Leti, Stallergenes, Bayer Schering, Ansell, Kryolan, UCB, MSD, DST, Sanofi-Aventis, and Procter & Gamble; is on the editorial board of the Journal of Allergy, the scientific advisory board of the German Society for Allergy and Clinical Immunology, and the Expert Commission “Novel Food” of the German Federal Ministry of Consumer Protection; is chairman of the European Academy of Allergology and Clinical Immunology, Dermatology Section; is head of the European Center for Allergy Research Foundation; is a committee member of the WHO Initiative Allergic Rhinitis and its Impact on Asthma; is a member of the World Allergy Organization Communications Council; and is secretary general of the Global Allergy and Asthma European Network. E. Mantzouranis, N. Aït-Khaled, C. E. Baena-Cagnani, A. Bush, M. Chan-Yeung, B. Chowdhury, J. M. Drazen, F. Kauffmann, N. Khaltaev, J. P. Kiley, M. R. Masjedi, Y. Mohammad, M. R. Partridge, A. Togias, and N. Zhong have declared that they have no conflict of interest.

    Draft reviewed by I. Agache (Romania), E. Aka-Danguy (Cote d'Ivoire), I. J. Ansotegui (United Kingdom), E. D. Bateman (South Africa), A. Belevskiy (Russia), A. Ben Kheder (Tunisia), K. Bennoor (Bangladesh), M. Bergna (Argentina), K. Bissel (France), L. Bjermer (Sweden), L. P. Boulet (Canada), A. Bourdin (France), P. J. Bousquet (France), P. A. M. Camargos (Brazil), G. W. Canonica (Italy), K. H. Carlsen (Norway), P. Chanez (France), N. Chavannes (The Netherlands), Y. Z. Chen (China), C.-Y. Chiang (Taiwan), R. Chiron (France), T. Chivato (Spain), J. Chorostowska (Poland), A. Chuchalin (Russia), D. J. Costa (France), P. De Boer (The Netherlands), L. Delgado (Portugal), A. T. Dinh-Xuan (France), D. Dokic (Macedonia), B. Dolen (United States), H. Douagui (Algeria), R. Dubakiene (Lithuania), Y. El-Gamal (Egypt), R. Gerth van Wijk (The Netherlands), M. Gjomarkaj (Italy), E. Hamelmann (Germany), L. Heaney (United Kingdom), P. H. Howarth (United Kingdom), M. Humbert (France), S. K. Jindal (India), G. Joos (Belgium), O. Kalayci (Turkey), M. A. Kaliner (United States), R. Kauppinen (Finland), M. Khadadah (Kuwait), Y. Y. Kim (Korea), N. B. Koffi (Cote d'Ivoire), V. Kolek (Czech Republic), M. Kowalski (Poland), P. Kuna (Poland), L. T. Le (Vietnam), W. B. Lee (Singapore), E. Lemarié (France), R. F. Lockey (United States), T. Maglakelidze (Georgia), B. Mahbouh (United Arab Emirates), C. Massé (France), N. Miculinic (Croatia), M. Morais-Almeida (Portugal), C. K. Naspitz (Brazil), H. E. Neffen (Argentina), E. Nizankowska-Mogilnicka (Poland), P. Noel (United States), K. Ohta (Japan), S. Ouedraogo (Burkina Fasso), N. Papadopoulos (Greece), G. Passalacqua (Italy), R. Pawankar (Japan), C. Picado (Spain), T. Popov (Bulgaria), D. Postma (The Netherlands), P. Potter (South Africa), H. Reddel (Australia), N. Rodriguez (Mexico), J. Rosado-Pinto (Portugal), L. J. Rosenwasser (United States), D. Ryan (United Kingdom), M. Salapatas (Greece), M. Sanchez-Borges (Venezuela), H. J. Schünemann (Canada), V. Siroux (France), J. C. Sisul Alvariza (Paraguay), R. Smith (United States), T. M. Sooronbaev (Kyrgyzstan), M. A. Tageldin (Egypt), V. Taggart (United States), N. C. Thomson (United Kingdom), A. Todo-Bom (Portugal), A. Valiulis (Lithuania), E. Valovirta (Finland), G. Viegi (Italy), M. Wickman (Sweden), A. Yanes (Argentina), A. Yorgancioglu (Turkey), O. Yusuf (Pakistan), M. Zamboni (Brazil), H. Zar (South Africa), M. Zitt (United States).

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