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Bacteria May Lurk on Your Showerhead

Researchers Say Some Microorganisms on Showerheads May Be Small Enough to Be Inhaled
WebMD Health News
Reviewed by Louise Chang, MD

Sept. 14, 2009 -- Showerheads in your home may harbor potentially infectious bacteria and enrich their growth, according to a new study.

Researchers from the University of Colorado sampled gunk, which they call biofilm, from 45 germy showerheads in nine U.S. cities, then analyzed the ribosomal RNA gene sequences from the swab samples to figure out exactly what microorgamisms lurked there. They compared them with swabs from water before it entered the showerhead.

"What we show is the showerhead biofilm contains Mycobacterium avium concentrations relative to other organisms 100-fold higher than in water [before it comes out of the showerhead]," says Norman R. Pace, the study's senior author and distinguished professor of molecular, cellular and developmental biology at the University of Colorado, Boulder.

The study is part of a larger effort the team is involved in, focusing on the microbiology of the indoor environment and how it may contribute to illness. The current study received funding from the National Institute of Occupational Safety and Health and the Alfred P. Sloan Foundation.

"We don't know a whole lot about Mycobacterium avium prevalence," Pace tells WebMD. "It's hard to detect and largely ignored.''

Researchers do know that infections caused by the Mycobacterium avium complex occur often in patients with conditions that hamper cellular immunity such as AIDS and in patients who have chronic lung disease such as emphysema, according to the Infectious Diseases Society of America.

But the infections are not reported nationally to the CDC, whose researchers suspect the infections are probably environmentally acquired.

Pace says his previous studies of swimming pools and their biofilms, which commonly include Mycobacterium avium, got him to think about showers and germy showerheads, leading to the current study, which is published online in the journal PNAS Early Edition.

Searching for Germs

Pace's team swabbed the interior surfaces of the 45 showerheads from nine U.S. cities, including New York City, and eight others in Colorado, North Dakota, Illinois, and Tennessee.

Though they found varied microorganisms, Pace says that particularly striking was the non-tuberculous mycobacteria such as Mycobacterium avium. ''Exactly how much Mycobacterium is coming out during the shower is not clear," he says, since the swab was taken from the showerhead itself.

Some of the particles coming from showerheads, he says, are tiny enough to be inhaled into the airways.

In the paper, the researchers write: "We conclude that showerheads may present a significant potential exposure to aerosolized microbes, including documented opportunistic pathogens."

Paces adds that the potential health risk needs more research, particularly in patients with compromised immune or pulmonary systems, such as those with AIDS or emphysema.

The new study gives a better sense of exactly how germy the showerheads are, Pace says, than earlier research, which focused on culture-based techniques rather than genetic sequencing.

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