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ICD Code: 493. Asthma

ICD Code: 493. Article Review
Title: Sears MR; "Descriptive Epidemiology of Asthma." The Lancet; V.350 (Suppl II); 10/97; p1
      DEFINING ASTHMA: An all-encompassing definition of asthma remains difficult to construct. Recent consensus statements from national and international expert panels have built on past definitions with the addition of specific cellular functions, and describe a disorder characterized by variable airflow obstruction; symptoms of wheeze, cough, dyspnea, and chest tightness; reversibility to bronchodilators and corticosteroids; increased airway responsiveness to a variety of stimuli; and evidence of inflammation in which eosinophils, mast cells, and lymphocytes together with a multitude of cytokines have important roles. Given the heterogeneity of the clinical forms of asthma a single definition seems remote, although genetic studies may help. The definition of asthma applicable to children with atopic sensitization may not adequately describe adults developing wheezing from occupational sensitization, or after respiratory tract infections, or even after stopping smoking. Among children there exist clearly different forms of wheezing requiring different definitions and very likely having different pathologies. Some authors differentiate early transient wheezing (with symptoms occurring before age 3 that do not persist to age 6) from wheezing with persistence beyond age 6. The former children have smaller airways and are more at risk from maternal cigarette smoking than maternal asthma or allergy, whereas risk factors for the latter include family history, serum IgE, and other manifestations of atopy.
      GLOBAL PREVALENCE AND MORTALITY: The global burden of asthma can be approximated from measured prevalence rates (reflecting incidence, duration, persistence, and recurrence of disease). If 10% of children and 5% of adults have asthma (figures that are conservative for western countries but may be overestimates in some developing countries), the global burden of asthma is on the order of 130 million people. Mortality rates from asthma in almost all western countries vary between 1 and 5 per 100,000, and result in some 60,000 deaths annually, many of which occur in young people and are potentially preventable.
      DIAGNOSIS: In the absence of a single easily recognized diagnostic marker of the presence or absence of asthma, the diagnosis in a clinical setting usually relies on the combination of a history of characteristic symptoms, and objective evidence of airway lability, demonstrated by spontaneously variable or reversible airflow obstruction with 15% or greater change in flow rate, a bronchoconstrictor response to histamine or methacholine, or daily or diurnal variability in peak expiratory flow. In earlier epidemiological studies, reliance was largely placed on questionnaire responses to determine "probable asthma" and "possible asthma," but these were unverified diagnoses. Most studies have found that 50% or fewer of those with recurrent wheezing consistent with asthma have been given that diagnosis, and that those so diagnosed generally have more severe disease. More recent epidemiological studies have added functional measurements, with abbreviated validated methacholine or histamine challenge protocols to demonstrate airway hyperresponsiveness and peak flow monitoring over 1 to 2 weeks to confirm or negate the symptom history suggesting variable airflow obstruction. Other ancillary investigations used in epidemiology, including the presence of atopy as determined by serum IgE levels or allergen skin prick test responses, facilitate the characterization of asthma rather than the certainty of the diagnosis.
      SYMPTOM PREVALENCE: International comparisons of prevalence and characteristics of asthma have been greatly facilitated by the completion of two major initiatives in asthma epidemiology, the European Commission Respiratory Health Study (ECRHS) and the International Study of Asthma and Allergies in Childhood (ISAAC). Preliminary data from both studies show 2-fold to 5-fold differences in crude prevalence rates in different regions depending on the symptoms compared. The range of asthma symptom prevalence in the ECRHS questionnaire was reported as follows: wheeze in past 12 months, 4.1% to 32.0%; wheeze with breathlessness, 1.4% to 16.3%; wheeze without a cold, 2.0% to 21.6%; walking with tightness in chest, 6.2% to 20.5%; walking with breathlessness, 1.5% to 11.4%; walking with cough, 6.0% to 42.6%; attack of asthma, 1.3% to 9.7%; treatment for asthma, 0.6% to 9.8%; nasal allergies and hay fever, 9.5% to 40.9%. The prevalence of asthma ever, wheeze ever, and wheeze in the past 12 months (respectively) among 13- to 14-year-olds responding to the ISAAC questionnaire was reported as follows: Adelaide, Australia, 22%, 40%, 29%; Sydney, Australia, 26%, 45%, 30%; Sussex, UK, 15%, 48%, 29%; Bochum, Germany, 4%, 33%, 20%; Wellington, NZ, 18%, 44%, 28%; Hamilton, Canada, 19%, 44%, 30%; Saskatoon, Canada, 12%, 36%, 23%; Bay of Plenty, NZ, 22%, 30%, not sought; Singapore, 21%, 29%, 10%; Hong Kong, not sought, 20%, 12%.
      UNITED KINGDOM: The prevalence rates of various symptoms in Aberdeen (UK) schoolchildren in 1989 were reported as follows: wheeze, 19.0%; shortness of breath, 9.4%; asthma, 10.0%; eczema, 12.0%; hay fever, 11.8%. In Aberdeen, essentially identical studies were undertaken in children 25 years apart. In 1989, the prevalence of wheeze and of diagnosed asthma had doubled compared with 1964. The prevalences of eczema and hay fever had also substantially increased, suggesting the increase in asthma related primarily to an increase in the prevalence of allergy. That study also provided evidence that the recognition of asthma had increased, because in 1989 the label of "asthma" was used in 52% of subjects with wheeze compared with only 21% in 1964. Among 12-year-old children in south Wales, the prevalence of a history of wheezing at any time increased from 17% in 1973 to 22% in 1988, and a history of asthma at any time from 6% to 12%. Exercise provocation testing suggested both mild and severe asthma had increased. As in Aberdeen, the prevalence rates of eczema and hay fever also rose over that 15-year period, from 5% to 16% and 9% to 15%, respectively. In an adult population, the prevalence of wheezy breathing in the past year increased from 21.0% in 1987 to 25.1% in 1990, and current asthma from 5.6% to 8.0%. In two UK birth cohorts (born in 1958 and 1970), the prevalences at age 16 of asthma or wheezy bronchitis in the past 12 months were 3.8% and 5.9%, respectively. It is noteworthy that no study has shown a decrease in prevalence over time.
      DISCUSSION: Reasons for increased prevalence of asthma, or increased allergy, may include changes in housing allowing greater proliferation of house-dust mites, therefore increasing both sensitization and exposure; effects of environmental factors including both outdoor and more pertinently indoor pollutants (the impact of passive smoking being the best documented); and perhaps changes in diet. The impact of early childhood infections, and their treatment, on the development of the immune system (and therefore on allergy) is currently of major interest.

Search Criteria: Text - The Lancet; V.350 (Suppl II); 10/97; p1