In Denver, one showerhead in the study with high loads of the pathogen Mycobacterium gordonae was cleaned with a bleach solution in an attempt to eradicate it, said Pace. Tests on the showerhead several months later showed the bleach treatment ironically caused a three-fold increase in M. gordonae, indicating a general resistance of mycobacteria species to chlorine.

Previous studies by Pace and his group found massive enrichments of M. avium in "soap scum" commonly found on vinyl shower curtains and floating above the water surface of warm therapy pools. A 2006 therapy pool study led by Pace and CU-Boulder Professor Mark Hernandez showed high levels of M. avium in the indoor pool environment were linked to a pneumonia-like pulmonary condition in pool attendants known as "lifeguard lung," leading the CU team into the showerhead study, said Pace.

Additional studies under way by Pace's team include analyses of air in New York subways, hospital waiting rooms, office buildings and homeless shelters. Indoor air typically has about 1 million bacteria per cubic meter and municipal tap water has rough 10 million bacteria per cubic meter, said Pace.

So is it dangerous to take showers? "Probably not, if your immune system is not compromised in some way," said Pace. "But it's like anything else -- there is a risk associated with it." Pace said since plastic showerheads appear to "load up" with more pathogen-enriched biofilms, metal showerheads may be a good alternative.

"There are lessons to be learned here in terms of how we handle and monitor water," said Pace. "Water monitoring in this country is frankly archaic. The tools now exist to monitor it far more accurately and far less expensively that what is routinely being done today."

In 2001 the National Academy of Sciences awarded Pace the Selman Waxman Award -- considered the nation's highest award in microbiology -- for pioneering the molecular genetic techniques he now uses to rapidly detect, identify and classify microbe species using nucleic acid technology without the need for lab cultivation. That same year he was awarded a MacArthur Foundation "genius grant" for his work.

Source: University of Colorado at Boulder