There's a well known paper by Dr. Falkinham on mycobacteria in the environment that circulates around here every now and again but I can't locate it. Bottom line is that NTM (non typical mycobacteria) are everywhere -- soil, air and water pipes. There are mitigation strategies, they take some doing but are very possible. Some people here continue to garden but take precautions (masking, wetting soil first to cut down on dust, etc).