House dust mite allergen levels in German day-care centers

We investigated the levels of the major house dust mite allergens, Der p 1 and Der f 1, in dust collected from various locations in 41 day-care centers from two German cities (Dusseldorf and Bonn). One hundred and thirty-seven (96%) of 143 samples yielded detectable amounts of house dust mite allergen (range, < 15 - 85,000 ng/g; interquartile range, 210 - 1,486 ng group I allergen [sum of Der p 1 and Der f 1]/g dust), and 24,(17%) of the samples (8/34 mattresses; 11/46 cushions/soft toys; 5/43 carpeted floors, 0/20 smooth floors) exceeded the proposed "threshold" level of 2,000 ng/g dust in 18 (44%) of 41 day-care centers. Der p 1 and Der f 1 could be detected in nearly an equal number of samples. The highest concentrations of house dust mite allergens were found in dust from mattresses (geometric mean, 1,103 ng/g dust) and cushions/soft toys (geometric mean, 1,004 ng/g dust). The allergen load per unit area from carpeted floors exceeded that from smooth floors by more than two orders of magnitude. In comparison with dust samples from private homes within the same geographical area, the mite allergen levels in mattress dust (RR, 0.34; Cl-95, 0.18-0.64) and floor dust (RR, 0.21; Cl-95, 0.09-0.49) from day-care centers were significantly lower (p < 0.001). We conclude that day-care centers should be included as potential places of additional exposure to house dust mite allergens if avoidance measures are taken.