Endotoxin exposure associated with respiratory health among European schoolchildren: The SINPHONIE study

Background: Evidence on the association between endotoxin exposure and respiratory health in children remains inconsistent, with limited research addressing school environments-key settings for daily exposure. This study investigates the relationship between classroom endotoxin levels and respiratory health among European schoolchildren. Methods: Within the EU-funded SINPHONIE project, endotoxin concentrations were measured in 285 classrooms across 102 schools in 22 European countries. A total of 5,140 children completed a standardized health questionnaire; 4,633 had endotoxin data, 4,170 performed spirometry, and 746 underwent fractioned exhaled nitric oxide (FeNO) testing. Findings: Endotoxin levels varied geographically, with the highest averages in Italy and the lowest in Finland. After adjusting for confounders, exposure to endotoxin levels at or above the median was associated with higher odds of upper and lower respiratory symptoms-runny nose, nasal obstruction, cough, dry throat, breathing difficulty, and feverishness-as well as reduced lung function (p < 0.05). Meta-analysis by WHO European clusters confirmed these associations, though region-specific analyses indicated a possible protective effect of endotoxin exposure in Northern Europe. Interpretation: Findings from SINPHONIE highlight classroom endotoxin as a potential environmental determinant of respiratory health. Reducing exposure in schools-currently an overlooked setting-may support respiratory well-being in children and inform future public health policies.