Prevention of airborne contamination and cross-contamination in germ-free mice by laminar flow.

The efficacy of horizontal and vertical laminar flow units (equipped with high-efficiency air filters) in the prevention of cross-contamination between cages and of contamination from outside has been demonstrated. With germ-free mice and using germ-free standard techniques for sterilization and for the transfer of germ-free mice into the cabinets via a standard entry lock, it was found that during an observation period of 2 weeks the animals remain ;negative'. Other experiments were performed with equally good results in cabinets equipped with a hinged flap, closing 95% of the open front side. When the flap was closed the air flow could be reduced accordingly, thus reducing the noise level and the risk of dehydration.Experiments made with germ-free mice in a ;down-flow unit' were also invariably good.In another type of experiment, cages with conventional mice were placed in the cabinets between cages with germ-free animals at varying distances. If all animals were maintained on wire mesh (to minimize the aerosol production of dust) and if the ;conventional' cages were at a distance of 10 cm. from ;germ-free cages' the latter remained bacteria-free during test periods of one week.The use of ;laminar flow isolators' for the isolation of human patients is mentioned.