Changing trends in sex specific prevalence rates for childhood asthma, eczema, and hay fever.

Numerous surveys of school-aged children have shown increasing asthma prevalence with a less publicized but noticeable change in the male to female ratio. We sought to confirm this change in the sex ratio in four questionnaire-based surveys and investigate possible explanations. Identical questionnaire surveys were performed in 1989 (n=3,390), 1994 (n=4,047), 1999 (n=3,540) and 2004 (n=1,920) in school-children aged 9-11 years. Over these 15 years the male to female ratio (M:F) significantly narrowed for wheeze (1.34 to 0.98:1 P < 0.0002), for asthma (1.74 to 1.02:1 P < 0.0001), for eczema (1.42:1 to 0.81:1 P < 0.0001) and for hay fever (1.46 to 0.93:1 P < 0.0001). The diagnosis of asthma in children with wheeze was more commonly made in boys in 1989 relative risk RR 1.32 (1.12, 1.56), even in those with accompanying eczema and/or hay fever RR 1.20 (0.99, 1.45). By 2004 this sex bias in diagnosis was no longer present, RR 1.01 (0.91, 1.12) for wheeze and 1.02 (0.85, 1.21) for those with wheeze and eczema and/or hay fever. From 1989 to 2004 no significant difference in sex distribution changes between older and younger children occurred, making secular trends in the onset of puberty in females an unlikely contributory factor. The disappearance of the bias to diagnose asthma in symptomatic males but not in females may be partly responsible for the narrowing of the sex ratio, but other factors such as those enhancing the expression of asthma and atopy in females may also be implicated.

A comparison of virus-associated and multi-trigger wheeze in school children.

To examine differences between virus-associated wheeze and wheeze associated with other triggers (multi-trigger wheeze) in elementary school children, we performed a cross-sectional school-based questionnaire study of 5,998 children mainly 7 to 12 years of age, with outliers 6 and 13 years of age. Using parent-completed questionnaires, we identified 522 children who wheezed only during upper respiratory tract infections (virus-associated wheeze), 1,186 children who wheezed on other occasions (multi-trigger wheeze), and 4,290 children with no wheeze. In comparison with children who had multi-trigger wheeze, children with virus-associated wheeze were more likely to be male, to be younger, and to have less frequent wheezy episodes. They were less likely to have night cough, shortness of breath or chest tightness, to have a personal or parental history of atopic disorders, to have a diagnosis of asthma, or to be receiving asthma treatment. Both types of wheeze were associated with social deprivation, a relationship that persisted after controlling for family smoking. Virus-associated wheeze is a common but diminishing problem in this age group, and the differences between virus-associated wheeze and multi-trigger wheeze already noted in pre-school children persist in this older age group.