If you have bad gum disease. does that mean the bacteria will spread to your bloodstream? if so is it preventable?

Dental intervention is critical if you possess "bad gum disease", as the future stability of your teeth is at high risk. If you do have an active severe infection, the possibility of sepsis is low, but local cellulitis could potentially commence. All of this can be fully reversed. Get proactive and see a dentist ASAP.

Yes and Yes. It has been widely published non well refereed dental journals that there is an association between gum disease and stroke, heart disease, kidney/liver/pancreas problems, pre-term deliveries, low birth weight infants, etc. The infection spreads through blood and lymphatic systems. The chance of sepsis is low. Just recently study published linking gum disease and brain micro-bleeds.

If you've neglected your oral health for a while, it's time to see a dentist for an evaluation. Festering bacteria from periodontal issues have been shown to contribute to a multitude of health problems.