Exposure to high endotoxin concentration increases wheezing prevalence among laboratory animal workers: a cross-sectional study

<p><strong>Background:</strong> Endotoxin from Gram-negative bacteria are found in different concentrations in dust and on the ground of laboratories dealing with small animals and animal houses. <strong>Methods: </strong>Cross-sectional study performed in workplaces of two universities. Dust samples were collected from laboratories and animal facilities housing rats, mice, guinea pigs, rabbits or hamsters and analyzed by the “<em>Limulus amebocyte lysate</em>” (LAL) method. We also sampled workplaces without animals. The concentrations of endotoxin detected in the workplaces were tested for association with wheezing in the last 12 months, asthma defined by self-reported diagnosis and asthma confirmed by bronchial hyperresponsiveness (BHR) to mannitol. <strong>Results: </strong>Dust samples were obtained at 145 workplaces, 92 with exposure to animals and 53 with no exposure. Exposed group comprised 412 subjects and non-exposed group comprised 339 subjects. Animal-exposed workplaces had higher concentrations of endotoxin, median of 34.2 endotoxin units (EU) per mg of dust (interquartile range, 12.6-65.4), as compared to the non-exposed group, median of 10.2 EU/mg of dust (interquartile range, 2.6-22.2) (p < 0.001). The high concentration of endotoxin (above median, 20.4 EU/mg) was associated with increased wheezing prevalence (p < 0.001), i.e. 61% of workers exposed to high endotoxin concentration reported wheezing in the last 12 months compared to 29% of workers exposed to low endotoxin concentration. The concentration of endotoxin was not associated with asthma report or with BHR confirmed asthma. <strong>Conclusion: </strong>Exposure to endotoxin is associated with a higher prevalence of wheezing, but not with asthma as defined by the mannitol bronchial challenge test or by self-reported asthma. Preventive measures are necessary for these workers.