Since MAC is everywhere it can also exist in handheld shower heads. Other than replacing your shower head (handheld or fixed) with an expensive Pall micro filter shower head, you can turn the hot water heater up to over 130 degrees. This will help diminish and possibly eliminate NTM/MAC.

From Dr. Falkinham's paper on subject:
"Raise Water Heater Temperature. Turn up your water heater to 130° F (55° C). NTM patient household plumbing that did not have NTM had higher hot water temperatures (130° F or 55° C or higher), compared to households whose hot water heater temperature was 125° F (50° C) or lower (Falkinham, 2011). Recent studies (09/01/15) have shown that raising hot water heater temperatures in 10 homes that had M. avium, resulted in disappearance of M. avium from 10 of the 10 homes by 12 weeks. That work is being written up for publication. We are continuing to look for M. avium in those households to be sure we are not selecting for heat-resistant NTM."

FYI - I have not seen the work that was being written up on the topic. Maybe someone else has?

I'm not sure what you mean by cleaning showerheads, but raising the hot water temp has been shown most effective, along with a periodic soak in vinegar. A recent update from the MAC conference is questioning whether the filters are effective.
We rely on a showerhead with big drops, high water temp and a strong exhaust fan. I also leave the room after shower until air clears.