Two main subtypes of wheezing illness? Evidence from the 2004 Aberdeen schools asthma survey

Abstract

To compare risk factors for wheezy bronchitis (WB) and multi-trigger wheeze (MTW) in pre-pubertal children along the spectrum of disease severity. Cross-sectional survey of children aged 7-12 yr in Aberdeen city primary schools in 2004 using parent-completed questionnaires as used in surveys in 1964, 1989, 1994, and 1999. Children were grouped into five categories: no wheeze in the past three years, non-severe wheeze triggered only by a cold (non-severe WB), non-severe wheeze triggered by other factors (non-severe MTW), severe WB, or severe MTW. Severe wheeze was defined as greater than four wheezing attacks, greater than or equal to one disturbed night per week, or speech limitation in the last 12 months. Questionnaires were returned by 3271 children (57.3%), of whom 7.4% had WB (6.1% non-severe and 1.3% severe) and 17.2% had MTW (9.4% non-severe and 7.8% severe). Severe disease was more frequent in children with MTW (31.8%) than in those with WB (5.1%). Whereas the prevalence of MTW had increased since 1964, the prevalence of WB had remained stable over this period. After adjustment for confounders, age had no influence on either wheeze type, and male sex was only associated with non-severe WB [OR 1.44, 95% confidence intervals (1.03-2.02)]. In the WB group eczema or/and hay fever in the child were more strongly associated with severe wheeze [OR 3.28(1.49-7.23) vs. OR 1.84(1.31-2.60)]. In the MTW group, this association was noticeably higher than in the WB group, but did not differ much between non-severe and severe wheeze [OR 5.46(3.70-7.20) and OR 6.01(4.1-8.75) respectively]. The presence of any allergic diseases in either parent increased the odds for non-severe and severe MTW at the same level of magnitude [OR 1.92(1.38-2.68) and OR 1.92(1.34-2.76) respectively], and statistically non-significantly for severe WB [OR 1.75(0.78-3.94)]. Living in a deprived area increased both severe WB and severe MTW, reaching statistical significance only for severe MTW [OR 1.96(1.39-2.78)]. Smoking in the house was associated with increased risk of WB and MTW of any severity. WB and MTW differ in prevalence trends and severity. Within severity levels, the influence of age, allergic diseases in children and parents also differed between these two wheezing subtypes.