I caught it through wearing earrings which were not gold but gold plated and had gone almost rusty. (I was young so didn't know putting rusty earrings in your ears would cause an infection!). My doctor didn't prescribe antibiotics but told me to clean the area daily with a mixture of warm water and bicarbonate of soda. Eventually it cleared up but I don't think it had much to do with bathing it. You can catch it by touching the blisters as far as I am aware. I was told to use a different towel to the rest of my family and to make sure I used a totally different towel to dry my ear from the rest of my body. It still comes back about every three months since I was about 10 and I'm 21 now. Usually if I leave any earrings in overnight or if I get stressed (weird I know!).
So many people have asked about impetigo in the past that information has been put on the home page of this site. However if you want to know more you could try looking here http://www.netdoctor.co.uk/diseases/facts/impetigo.htm
It is very contagious and is caught easily by contact. My son caught it by playing rugby at school, obviously from another child and he had it really badly under his arm. Eventually it spread all over his face. I caught it from him and it infected two fingers badly and the back of my head where I scratched it! Antiobiotics are very effective. Towels, bedding, etc. should not be shared. It is quite a common condition, especially in school children.