BEST OF 2009: Are you sick and clean?

U. COLORADO (US)—Millions of Americans are getting a dousing of pathogenic bacteria along with their daily showers, a new study finds. Researchers have discovered that water spurting from showerheads can distribute pathogen-filled droplets that suspend themselves in the air and can easily be inhaled into the deepest parts of the lungs.

The findings by a team from the University of Colorado at Boulder indicates that increases in pulmonary infections in the United States in recent decades from so-called “non-tuberculosis” mycobacteria species like Mycobacterium avium may be linked to people taking more showers and fewer baths, says the study’s lead author Norman Pace.

For the study, researchers used high-tech instruments and lab methods to analyze roughly 50 showerheads from nine cities in seven states that included New York City, Chicago, Denver, Tennessee, and North Dakota. They concluded about 30 percent of the devices harbored significant levels of M. avium, a pathogen linked to pulmonary disease.

It’s not surprising to find pathogens in municipal waters, Pace says, but some M. avium and related pathogens were found clumped together in slimy “biofilms” that clung to the inside of showerheads at more than 100 times the “background” levels of municipal water.

“If you are getting a face full of water when you first turn your shower on, that means you are probably getting a particularly high load of Mycobacterium avium, which may not be too healthy,” he explains.

Symptoms of pulmonary disease caused by M. avium can include tiredness, a persistent, dry cough, shortness of breath, weakness, and “generally feeling bad,” says Pace, a professor in the molecular, cellular, and developmental biology department. Immune-compromised people like pregnant women, the elderly and those who are fighting off other diseases are more prone to experience such symptoms.

“There have been some precedents for concern regarding pathogens and showerheads,” says Pace. “But until this study we did not know just how much concern.”

During the early stages of the study, the team tested showerheads from smaller towns and cities, many of which were using well water rather than municipal water.

“We were starting to conclude that pathogen levels we detected in the showerheads were pretty boring,” says first author Leah Feazel. “Then we worked up the New York data and saw a lot of M. avium. It completely reinvigorated the study.”

In addition to the showerhead swabbing technique, Feazel took several individual showerheads, broke them into tiny pieces, coated them with gold, used a fluorescent dye to stain the surfaces and used a scanning electron microscope to look at the surfaces in detail. “Once we started analyzing the big metropolitan data, it suddenly became a huge story to us,” she says.

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, says 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.

Pace says a 2006 therapy pool study in which high levels of M. avium in indoor pool environments was linked to a pneumonia-like pulmonary condition known as “lifeguard lung” led to the current study.

So is it dangerous to take showers? “Probably not, if your immune system is not compromised in some way,” says Pace. “But it’s like anything else—there is a risk associated with it.”

Because 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,” Pace concludes. “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.”

The study appeared in the Sept. 14 online edition of the Proceedings of the National Academy of Sciences and was supported by the Alfred P. Sloan Foundation.

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