Effects of allergen exposure on methacholine and AMP-induced air trapping in pollen-sensitive subjects

Prevalence of airway hyperresponsiveness and its seasonal variation in children with asthma

BACKGROUND

Airway hyperresponsiveness (AHR) is a key feature of asthma and can be detected using various bronchoprovocation tests. In pediatric populations, the percentage of a positive methacholine challenge test (MCCTs) in children with asthma varies among studies, and some have reported seasonal variability. However, these studies have mostly been conducted in temperate regions. This study evaluated the prevalence of AHR to methacholine and its seasonal variation in asthmatic children in Taiwan, a subtropical country.

METHODS

A total of 276 children with asthma and their MCCT results were retrospectively reviewed. All were diagnosed with asthma and received asthma controllers regularly. They were assigned to four season groups depending in which season MCCTs were administered, with seasons categorized by the Central Weather Bureau of Taiwan. Subgroup analyses, including for sex, age, and atopy level, were compared for seasonal difference.

RESULTS

The prevalence of methacholine hyperresponsiveness was 70.7% (n = 195), and the children who were younger and had higher total serum IgE were more sensitive to methacholine (p = 0.019 and p < 0.005, respectively). No significant difference in AHR prevalence among seasons was observed (p = 0.480). The percentage of borderline, mild, and moderate severity of MCCT results was almost equally distributed among the seasons. In subgroup analysis, the children with a higher IgE level (≥75th percentile of all data) had a higher proportion of positive MCCTs in summer (88.6%, p = 0.016).

CONCLUSION

In total, 70% of the children with asthma in Taiwan had AHR to methacholine, which varied among seasons. Children with a higher total serum IgE level may be more seasonally dependent, particularly in summer.

High ambient Cladosporium spores were associated with reduced lung function in schoolchildren in a longitudinal study

BACKGROUND

In our previous longitudinal study, we found that exposure to current levels of ambient total fungal spores was related to a reduction of childhood lung function. However, the biological properties of various taxa of fungal spores varied greatly, as well as their health effects. In this study, we aimed to determine whether any specific fungal spores were responsible for observed changes in lung function.

METHODS

Measurement of lung function was conducted for 100 elementary and middle-school students on 5-10 occasions from October 2007 to November 2009 in New Taipei City, Taiwan. During the week of each lung function measurement, continuous daily concentrations of fungal spores were measured from Sunday to Saturday. The counts of fungal spores belonging to specific taxa were identified. A mixed-effect model with repeated measurements was used to analyze the association of lung function and exposure to each specific taxon of fungal spores. Forward stepwise regression was applied to determine which specific fungal spores were the most closely related to lung function changes. The non-linear relationship was examined using a generalized additive model. The piecewise linear regression was then applied to determine the threshold value.

RESULTS

A total of 824 measurements were obtained from 100 participants. Among all the species of fungal spores, only Cladosporium spores were found to be negatively associated with forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) one day later. This association was stronger than the one between the total spore counts and lung function. The threshold of exposure where lung function effect became observable was approximately 1,500 spores/m(3).

CONCLUSION

This study showed that ambient Cladosporium was most strongly associated with the observed lung function changes among schoolchildren. Replication of these preliminary findings in other geographic areas with different populations would be warranted.