There's a lot of b@llocks about cabin air - especially from the press. The only figures I remember from my type tech are for the B747-400. The flow of cabin air with all 3 packs at high flow means the whole cabin air gets changed in about 8 minutes. In the cruise with 3 packs at low flow and all the recirc fans on, the air is changes every 12 minutes. Compared with the average operating theatre (every 20 minutes) or an average office block (every hour) this isn't bad. Also, the recirculated air is passed through the same type of filters used in operating theatres - although how often they are changed is a different matter.
I think these figures are correct, but my 744 type tech was a while and two types ago. Cornish Jack will know the correct figures if I'm wrong.