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.
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.