I think experience in mental health / psych nursing is transferrable to any area of nursing you may want to move into, public health included. In any interviews you have, you can highlight your experience with therapeutic communication, patient teaching, and thinking-out-of-the-box resource finding. You'll find in many public health positions that your communication skills are your most valuable skill as you rely more on that for direct patient/client interactions or working with the community than things like lab values or physical assessment findings.
I started work in public health straight out of nursing school, so I can't speak to the transition you'll have to do. There are nursing positions in public health that deal with mental health. I've seen VA nurse case managers for mental health clinics, a nurse in my health department focuses on pregnancy-related depression and anxiety disorders and provides her expertise to home visit nurses who deal with pregnant and parenting women and also provides trainings to local health care providers and community organizations to help them recognize and refer pregnant/post partum women who are experiencing those problems. There are some nurses where I am that do mental health first aid trainings (Mental Health First Aid
) in the community. If substance abuse is your bag, there is a world of things opening up with syringe exchange programs that may involve nurses. Jobs like these vary in availability depending on your location though, so you should snoop around your local public health department and state health department websites to look at what programs and services are offered that might be related to mental health and consider the possibility of a move if there isn't anything locally available. Another thing to look at would be disaster service organizations that might use psych nurses for psychological first aid in disaster response.
I would encourage you to consider joining your state's public health association to get connected to public health in your area. You can network to learn who the major public health players are in your state,, get job listing notifications, and maybe even find a mentor to help you transition to public health. Find your state or local chapter here: State & Regional Public Health Associations
Good luck and keep us posted!