Efficiency of air filter sets for the prevention of airborne infections in laboratory animal houses

Air filter sets (classes EU6 and EU9, or EU6 and S) were tested for their efficiency in protecting laboratory animals against potential airborne infections. Flexible-film isolators were used as a smaller scale model. In the first experiment, lasting 7 months, it was tested whether minute virus of mice (MVM) was able to penetrate the airfilters between one isolator containing experimentally infected mice and another with MVM negative mice. In the second experiment we tested whether microorganisms in the incoming air were able to penetrate air filter sets. To assess this gnotobiotic mice in an isolator were monitored for 9 months for changes of their microbial flora. In both experiments a combination of EU6 and EU9 air filters proved to be sufficient to maintain the microbiological status of the animals. The same combination of medium efficiency filters (EU6 and EU9) is used on the air supply to 4 SPF-barrier units in which infections with MVM occurred repeatedly soon after the initial stocking. After a thorough disinfection no reinfection has been detected to date. This demonstrates that the relatively low efficiency of the air filters was not the cause of the repeated infection. The procedure for disinfection is described.