Treatment of whole houses with liquid nitrogen for control of dust mites

A large volume of liquid nitrogen, (120-150 L) was applied to the houses of 4 asthmatic patients, and the mite densities of the floor dust from these houses were monitored every 2 wk for 4 mo from July to November 1989. The 1st liquid nitrogen treatment was applied in early August and decreased the mite densities to 20-44% of the pretreatment level in all cases, but they returned to the pretreatment level 3-4 wk later (on 3 occasions). The 2nd liquid nitrogen treatment was applied in early September and decreased the mite densities to 6-27% of the pretreatment level within 3 wk in all cases. However, mite numbers again increased to the pretreatment level 4 wk after treatment. The 3rd treatment was applied in mid-October and reduced the mite densities to < 6% of the pretreatment level within 2 wk, and mite numbers remained low thereafter. The results suggested that using liquid nitrogen to freeze houses reduces mite numbers, but that mite recolonization of the houses is an important problem.