We recently (July 18) had friends stay with us for a week. They brought their 5 healthy well cared for dogs. The dogs have been on Frontline since May. The day after they left, we found fleas on the sofa.We flea bombed 2 times. Now we are having problems in the bedroom where they slept with people getting bit on their legs.Vacuuming revealed fleas in the carpet. I am ordering your sticky traps and the powder. I am vacuuming daily. How did we get fleas? The animals did not show signs of fleas from their reports and they tell us they do not have fleas in their homes. Could they be carriers? The incubation period seems too short ( the day after they left) for the dogs to be a problem. I need to understand to prevent this from occurring again. Thanks!