Evil spirits can not transfer to workers during deliverance sessions unless some right is given to the evil spirit by the worker. It is not common for this to happen.
I have had demons to ask me if they could come into me. My answer is definitely no. Some people practice exorcism. Exorcism is the practice of inviting the demon in someone to come within you. You would plan to cast out the demon later. As Christians we practice deliverance, not exorcism.
I do a lot of mass deliverance for groups of Christians. I do not believe that evil spirits can transfer from one person to another during mass deliverance. If I thought this could happen, I could not do mass deliverance. I have been doing mass deliverance in churches, homes, hotels, motels, jails, prisons and public places for around thirty-three years and have not found that to be a problem for me or for the Christians.
I do a lot of personal deliverance over the telephone, in my home and in public places such as churches. This is the most powerful type of deliverance; it is a one-on-one encounter. I have not had problems of transfer of spirits between those involved. With permission of the person, I lay hands on the forehead and shoulder. This is the most powerful way of personal deliverance for myself ministering to another Christian.
A spirit can not be within someone unless it has a legal right before GOD to do so. The right is given by sin of that person or someone who was in spiritual authority over the person. It is very important to take away the legal right before casting out the demon. If the legal right is not taken away through prayer by the individual, I believe the demon has a right to come back into the body.
Demons can not just transfer from person to person unless GOD allows them to do so. This means that the person must agree or someone in authority must allow this to happen such as a parent.
Demons within one person can be attracted by demons within another person. An example would be homosexual demons within two persons. The homosexual demons would attract the two people to have sodomy.