Objectives The relationship between indoor air exposure to fine particulate (PM_2.5) and asthma symptoms in children is uncertain. The aim of the present study was to relate PM_2.5 exposure to indices of asthma severity and control.

Methods Children with asthma were recruited. Disease severity was determined by questionnaire and spirometry. Asthma control was assessed by 5-day peak flow variability and children's asthma control test (CACT) on the first and fifth day of peak flow testing. Concentrations of PM_2.5 were measured over a 24-h period in the living room and the child's bedroom.

Results 22 children were recruited, mean age 11.0 years. Across the 22 homes the median time weighted average (TWA) PM_2.5 concentration (range) in the living room was 7.4 mg/m3 (2.0–150.0) and for the bedroom was 5.6 (3.1, 11.1) mg/m³ (p=0.04 for comparison with living room). As expected, there was a significantly higher mean TWA PM_2.5 in the living rooms and bedrooms of the seven homes where smoking was reported; 22.0 mg/m³ for living rooms in smoking homes and 4.7 mg/m³ for non-smoking homes, p=0.001. There was a positive association between TWA PM_2.5 in the living room and peak flow variability (r=0.51, p=0.027, see Abstract P77 Figure 1) and a negative association between TWA PM_2.5 in the living room and CACT on day 5 (r=−0.48, p=0.037). TWA PM_2.5 exposure was not related to indices of asthma severity including FEV₁ and treatment. Peak PM_2.5 concentration was not associated with any outcome.

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Abstract P77 Figure 1

Conclusions This small study suggests that even at relatively low concentrations, there is an exposure-response relationship between increasing indoor air PM_2.5 concentrations, increased airway variability and poorer asthma control in children.