Long-term exposure to air pollution and lower respiratory infections in a large population-based adult cohort in Catalonia

• Air pollution is a recognized risk factor for Lower Respiratory Infections (LRIs) among children. • Few studies investigated this association among adults and results were inconsistent. • Reductions in long-term air pollution, even at low levels, may contribute to fewer LRI-related hospitalizations. • Older or hypertensive individuals and males are particularly vulnerable to the effects of air pollution on LRI-hospitalizations. Evidence is limited regarding the role of air pollution in acute lower respiratory infections among adults. We assessed the influence of long-term air pollution exposure on hospital admission for lower respiratory infections and whether there are vulnerable subgroups. We used a populational cohort in Catalonia, Spain, comprising 3,817,820 adults residing in Catalonia as of January 1, 2015. Air pollution exposure was assigned to individuaĺs residential address using locally-developed models. We characterized the concentration–response functions between long-term air pollution exposure and hospital admission for lower respiratory infections between 2015 and 2019. We assessed interaction between exposure and clinical and socio-economic factors on multiplicative and additive scales. An interquartile range exposure increase was associated with an 8 % (95 % Confidence Interval: 5 %–11 %) for Nitrogen Dioxide, 10 % (95 % Confidence Interval: 8 %–13 %) for Particulate Matter with diameter equal to or smaller than 2.5 µm, 5 % (95 % Confidence Interval: 3 %–7%) for Particulate Matter with diameter equal to or smaller than 10 µm and 18 % (95 % Confidence Interval: 14 %–22%) for ozone (adjusted by Nitrogen Dioxide) increase in hospital admissions for respiratory infections. Concentration-response functions were non-linear, with steeper slopes at exposures below the median or at most extreme high values. Associations were consistently greater for individuals over 65 years or with hypertension diagnosis and males. Long-term exposure to air pollution was positively associated with hospital admission for lower respiratory infections. Individuals who were older than 65 years, hypertensive or male were most vulnerable.