The geometric mean concentration of endotoxin was
119 EU m2 day1, ranging between 11.2 and 1077 EU m2 day1.
Concentrations of endotoxin were significantly negatively associated
with area per person in the univariate model (p ¼ 0.01,
Table 4). This association lost significance in the multivariate
model. However, it remained as the most important variable in the
model, with p ¼ 0.08. Similar to our findings, two other studies by
Refs. [25,17] measured significantly higher levels of endotoxin in
dwellings occupied by higher number of persons and in 10 California
homes significant correlations have been found between
occupancy and endotoxin exposure [14]. In another study differences
in endotoxin exposures have been found when occupants
were absent from their home for two weeks. During occupancy the levels of endotoxin were 650 EU m2 day1 while during occupant
absence the levels dropped to 39 EU m2 day1 (average values)
[35]. Thus, the presence of occupants seems to increase the concentration
of airborne endotoxin considerably.