© 2006 American Thoracic Society
Does Most Asthma Really Begin during the Preschool Years?To the Editor:Prospective population-based studies, such as that of Morgan and colleagues (1) describing the natural history of asthma to age 16, are important to avoid bias from (1) studies of referred patient populations that are prone to sampling bias ("referral" bias) and bias from (2) retrospective medical record reviews that are prone to ascertainment and "diagnostic" bias. In their Introduction, Morgan and coworkers stated: "It now seems established that, in the majority of cases of persistent asthma, symptoms begin during the preschool years...." (1) However, their data indicate that less than half of adolescent asthma was present at age 3. At all ages up to 16, "late-onset wheeze" (at age 6 but not at age 3) was numerically greater than "persistent wheeze" (present at age 3) (Table 1). At ages 13 and 16, there were more infrequent and frequent wheezers in the two "preschool phenotypes" labeled "non-wheezers" (at ages 3 and 6) and late-onset wheezers combined than in the "transient early wheezers" (at age 3) and persistent wheezers (Figure 2). These data suggest that the majority of adolescent asthma was not present in children whose first symptoms began in the preschool years (age 3, as compared with age 6 or later). Morgan and coworkers cited an editorial (2) referencing Yunginger and colleagues (3) to support the statement that "most persons of any age who have chronic, persistent asthma have their first symptoms during their preschool years (2)." However, Yunginger and coworkers (3) performed a medical record review that is inherently subject to ascertainment bias. They also excluded asthma in any subject with an FEV1 less than 50% (this "diagnostic bias" will exclude adult asthma associated with fixed obstruction [4]). In the absence of a physician diagnosis, they accepted nonsmoking and several markers of clinical atopy as adjunctive criteria to classify "definite" asthma. A meta-analysis casts doubt that asthma is predominantly an atopic disease (5). Hence, including atopy (and, I would add, nonsmoking) as a "tie-breaker" to identify asthma also introduces diagnostic bias against adult asthma, the majority of which is clinically nonatopic. On the other hand, a more rigorously designed, prospective, population-based study documented a stable incidence of asthma (0.30–0.35 per 100 subject years) throughout adulthood (6). My conclusion is that it may not be so well established that most asthma begins in the preschool years, or even in childhood. What do the authors think?
Dean Medical Center, Madison, Wisconsin FOOTNOTES Conflict of Interest Statement: D.L.H. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
