Rabbits can't get colds - it's just not possible. What they can get is respiratory tract infections. These can be mild or they can be horrendous, depending on how well the rabbit's immune system can cope with it. Nearly all rabbits carry the bacteria responsible, but it lies dormant until the immune system is compromised - such as from another illness, stress or big temperature changes. It can also be triggered by irritation of that area, such as a foreign body (dust etc) up the nose, use of air-fresheners/scented candles/cigarettes etc in the same room as the rabbit or dental problems. You cannot 'cure' the bacteria, it will never go away, but it can be managed and if your rabbit's immune system is strong, symptoms won't necessarily have to come back.
Sometimes with the help of antibiotics the bacteria can be subdued enough for the rabbit's immune system to deal with it and there will be no reoccurances, but often it is an illness that will reoccur throughout the rabbit's life. The treatment for a respiratory tract infection is antibiotics, and sometimes people also use an immune support, a nebuliser or medication to make the mucus more runny to flush out the bacteria.
The problem is that the longer the rabbit has the infection, the higher the chance of scarring in the airways. My rabbit will have issues for the rest of his life due to scarring in his lungs, which the vet thinks is due to his previous owner not having this illness (commonly known as 'snuffles') treated. It frequently reoccurs, often for months at a time, and there is also a higher risk for him when going under GA. So I would really urge anyone whose rabbit has symptoms of this illness to seek a rabbit-savvy vet, to try and knock the illness on the head and prevent permanent damage. If in doubt, always see a vet who is qualified in rabbit medicine, such as a rabbit specialist or an exotic vet. A 'small animal' vet or normal vet is not qualified in rabbit medicine. I feel I should also mention that, despite having this chronic illness, his chest ALWAYS sounds clear and sometimes the only symptom is running eyes or a damp nose - rabbits should never have running eyes or noses. These may seem like small symptoms but they should not be ignored.
*gets off soap box*
