Bronchiolitis, air pollution have ‘synergistic effect’ on asthma risk

By Mark Cowen, Senior medwireNews Reporter

Results from a Korean study show that a history of bronchiolitis plus exposure to increased levels of air pollution "synergistically" increases a child's risk for asthma.

The researchers also found that children with both risk factors - particularly atopic children - had significantly reduced lung function compared with other children.

"Together, these findings suggest that environmental control may improve respiratory health in children with atopy or bronchiolitis," say Soo-Jong Hong (University of Ulsan College of Medicine, Seoul) and team.

The researchers conducted a 2-year follow up study of 1743 children, aged a mean of 6.8 years at enrolment, from 16 elementary schools in seven Korean cities.

The children were assessed for asthma, allergies, and lung function at enrolment and follow-up, and exposure to air pollution over the previous 5 years at enrolment was estimated using a geographic information system.

After accounting for factors such as age, gender, body mass index, and parental allergy history, the researchers found that exposure to increased levels of ozone, defined as greater than the mean of 10.32 parts per billion, was associated with airway hyper-responsiveness at enrolment (odds ratio [OR]= 1.60) and current wheezing (OR=1.92). However, exposure to higher levels of air pollution was not associated with asthma.

By contrast, the risk for physician-diagnosed asthma was significantly increased among children with a history of bronchiolitis (OR=2.86), as was the risk for current wheezing (OR=1.94), compared with those without such a history.

However, children with both a history of bronchiolitis and exposure to higher levels of ozone had an even greater risk for asthma (OR=3.81), current wheezing (OR=2.73), and airway hyper-responsiveness at enrollment (OR=2.96), compared with children without these risk factors.

The researchers also found that the negative respiratory effects of air pollution combined with a history of bronchiolitis were greater in atopic than nonatopic children.

Hong and team conclude in Allergy: "This study revealed that there may be a synergistic effect between air pollution… and bronchiolitis in the development of childhood asthma."

They add: "The underlying mechanism may involve increased airway hyper-responsiveness and decreased lung function."

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