This is what he said Re this issue:
Dear Tamara:

Thank you for your reply and request for further information.

In a study of Philadelphia suburb patients, we discovered that raising the water heater temperature setting to 130 F or higher led to the disappearance of Mycobacterium avium from samples of household water, including showerheads.

That might surprise some as a showerhead will be delivering both heater (hot) and unheated water (cold). Yes, the source of water from the water heater is cold water, but in most municipalities the water delivered to homes has low numbers of NTM. My colleagues and I believe that the water heater is where NTM grow and are mixed with the cold.

We haven't tested "tank-less" or "instant" water-heaters, but logic suggests there should be no growth of NTM, as those water heaters don't have a large tank.