Endotoxin, a ubiquitous component of Gram-negative bacteria, is an important bioactive environmental factor linked to paediatric asthma incidence and severity in epidemiological studies.1 In challenge studies, acute effects of endotoxin exposure include bronchoconstriction, airways inflammation and airways hyper responsiveness.2 A recent literature review supported a causal association between house-dust endotoxin exposure and acute asthma exacerbations.3

Observational repeated measure studies employing personal monitors can be used to precisely measure endotoxin exposures encountered in the domestic setting, and to assess the timing and magnitude of the dose–response. In this way, effects of acute exposures can be studied in populations that could not ethically undergo exposure challenges, such as children and those with more severe asthma. Using this approach, Rabinovitch et al4 studied 14 mostly African–American children who attended a school set up for children with difficult to control asthma in Denver. Children in this study had symptoms on average 2–3 times a week indicating uncontrolled asthma despite use of inhaled corticosteroids given at school. Personal endotoxin exposure in this study was associated with a doubling of the odds of experiencing asthma symptoms …