Fahlbusch et al. 2000. The investigators attempted to quantify the amount of grass pollen allergen in settled dust samples collected from indoor environments.  Seasonal fluctuations of the allergen were also studied.  It was found that Phl p 5 allergen was present indoors year-round.  Peaks occurred during peak outdoor pollen season; however, allergen was detected outside pollen season.  In addition, indoor levels mimic outdoor levels during the pollen season, but were independent outside the pollen season.