Introduction: Larger population-based studies on the prevalence and risk factors associated with small airway obstruction (SAO) are lacking. Recently, evidence from China associated exposure to particulate matter of size ?2.5 µm (PM2.5) as a potential risk factor for SAO whose prevalence was high (43.5%). In our study, we hypothesized that lesser air pollution levels were associated with a lower prevalence of SAO in Switzerland.

Methods: PneumoLaus is based on the CoLaus cohort that phenotyped a random population sample in Lausanne, Switzerland. SAO was defined by maximum mid-expiratory flow (MMEF) <65% of predicted value (PV) or MMEF <lower limit of normal (LLN). We performed bivariable and multivariable analyses with MMEF criteria, age, gender, BMI, respiratory symptoms and smoking status. We utilised annual mean PM2.5 values from the Swiss national database as a measure for air pollution.

Results: Overall, 3?351 individuals performed spirometry (97.6% Caucasian), of which 12.7% (n=425) had MMEF<65%PV and 5.0% (n=167) MMEF<LLN. We observed a significant correlation between age, smoking status, cough, sputum, dyspnoea, and both MMEF<65%PV and MMEF<LLN. We found a positive association with age >65 years only for MMEF<65%PV. The national average ambient PM2.5 concentration was 14.1 µg/m3 in 2010 and 6.3 µg/m3 in Lausanne in 2017. 

Conclusion: Utilizing the MMEF <65%PV criteria can lead to SAO overdiagnosis in elderly individuals. The prevalence ?12.7% of SAO in our study compared to data from Asia could be related to lower PM2.5 exposure and/or ethnicity. Our results highlight the need for strategies focused on air quality as a determinant for respiratory health.