TORONTO — Cleanliness may be next to godliness, but when it comes to showers it may also be next to germiness.
That’s because showerheads can harbour a cornucopia of microbes, including the organism Mycobacterium avium that can cause lung infections in susceptible people.
After analyzing almost 50 showerheads in nine U.S. cities — including New York City, Chicago and Denver — researchers at the University of Colorado at Boulder found that up to 30 per cent showed evidence of colonization by Mycobacterium avium.
M. avium and related pathogens were found clumped together in slimy “biofilms” that gunked up the inside of showerheads at more than 100 times the “background” level found in municipal water supplies.
(The researchers did not find M. avium in showerheads with a water supply from a well.)
Researcher Laura Baumgartner said the bacteria can spew out of a showerhead in aerosolized water droplets and be breathed into the lungs.
“We’re guessing that first burst when you first turn the shower on is the most worrisome.”
While getting a face full shouldn’t pose a problem for most people, those with underlying medical conditions could be at risk for infection, said Baumgartner, co-author of the study published in the online edition of the Proceedings of the National Academy of Sciences.
“For the average person, this isn’t a big concern, it’s not something that’s likely to be a problem if you have a normal immune system,” she said Monday from Boulder, Colo.
“For people, particularly with cystic fibrosis or AIDS or the elderly, where your immune system is a little bit compromised, then this can actually be an issue.”
Baumgartner said cases of lung infection from “non-tuberculosis” mycobacteria species like M. avium have been steadily rising in the last century, and many researchers have hypothesized that the increase may be linked to more people taking showers than baths.
Dr. Andrew Simor, an infectious disease specialist at Sunnybrook Health Sciences Centre in Toronto, said the Colorado study is interesting because of the means used to detect M. avium: the researchers used DNA analysis instead of the usual cell-culturing method.
But Simor, who was not involved in the research, said the study “doesn’t demonstrate anything that wasn’t already known.”
“We’ve known for decades that water . . . water that comes from our taps and faucets in the kitchen, or in our showers in our homes, in hotels or whatever, this source of water is not sterile,” he said.
“It has micro-organisms or bacteria in it.”
Infections resulting from exposure to pathogens from these sources “occur very uncommonly,” he said. “They are not a common source of infection, even in people who are immuno-compromised.”
Even so, Baumgartner said people with severely suppressed immune systems might want to take steps to avoid the risk.
Studies have shown that M. avium and related bacteria cannot be eradicated from showerheads with bleach, so the researchers recommend that people install a metal showerhead — bacteria don’t grow as well on metal as on plastic — and change the devices every six months.