The relationship between air pollution from heavy traffic and allergic sensitization, bronchial hyperresponsiveness, and respiratory symptoms in Dutch schoolchildren - Children's Health

Environmental Health Perspectives, Sept, 2003 by Nicole A.H. Janssen, Bert Brunekreef, Patricia van Vliet, Francee Aarts, Kees Meliefste, Hendrik Harssema, Paul Fischer

Population. All children in classes 4-8 (7-12 years old) were invited to participate in the study. Parents of all children were asked to complete a questionnaire, and all children were invited to participate in lung function testing. In addition, children in the four highest classes (classes 5-8, 8-12 years old) were invited to participate 4n tests of BHR and of sensitization to common allergens (both blood sampling and SPT). Parents were asked to give written informed consent for all parts of the study separately. Measurements were conducted at the schools, in the period from April 1997 through July 1998. The study protocol was approved by the medical ethical committee of Wageningen University (where the principal authors were employed when the study was being prepared and conducted).

Exposure Variables

Traffic characteristics. Traffic counts were obtained from the Ministry of Public Works, which routinely collects counts for all motorway stretches in the Netherlands using induction loops. This method distinguishes vehicles shorter than and longer than 5.1 m, which we classified as cars and trucks, respectively. Weekday counts for 1997 were used. Distances of the schools to the motorways were measured using maps at 1:1,000 or 1:1,500 scale. Distances from the children's homes to the motorway were assessed using the geographic information system (GIS) Arc-Info (Environmental Systems Research Institute, Redlands, CA, USA).

Air pollution measurements. Outside each school, weekly averaged measurements were made of P[M.sub.2.5], N[O.sub.2], and benzene. Reflectance of P[M.sub.2.5] filters was measured as a proxy for elemental carbon (EC), a major part of diesel soot. The relationship between this proxy and actual measurements of EC was studied in a subsample, and a high correlation was established (Janssen et al. 2001). We made 5-10 measurements for each school, from April 1997 through May 1998. Annual average concentrations were calculated, after standardizing for differences in the background concentrations during the measurements. Details about the air pollution measurements and the calculation of the annual average air pollution concentrations are given elsewhere (Janssen et al. 2001). Outdoor benzene concentrations were strongly influenced by local sources (e.g., presence of a gasoline station) and were therefore not included in the data analysis for this report. Classroom measurements were also conducted, but because these measurements were conducted only during school hours ([ or -] 28 hr/week, weekdays only), classroom concentrations were also not considered as exposure variables in this report.

Questionnaire. We used the ISAAC questionnaire to measure symptoms of asthma and allergic disease in the children (Asher et al. 1995). We used the questions on wheeze in the past year, nasal symptoms together with itchy or watery eyes in the past year, itchy rash in the past year, bronchitis in the past year, phlegm without a cold in the past year, asthma ever, hay fever ever, and eczema ever as end points. In addition, the questionnaires included questions on potential confounders such as age, sex, and various exposure variables (among others, housing characteristics, possession of pets, and passive smoking).