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.
Until more research is done, Pace suggests inspecting your showerhead. If it's full of crusty crud, he says, "Get a new showerhead." He prefers all metal models to plastic, saying that plastic is more conductive to microorganisms sticking.
His hygiene advice: While a normal, healthy person need not be concerned, he says those with immune system or lung problems may want to take baths instead of showers.
Not so fast on ditching your shower, says Aaron E. Glatt, MD, a spokesman for the Infectious Diseases Society of America and president and CEO of the New Island Hospital in Bethpage, N.Y., who reviewed the study for WebMD.
"Nobody should be changing their personal hygiene preferences based on this article," Glatt says.
The research, he says, is a basic science investigation. "Before a basic science study can be translated to practical clinical advice, there needs to be a lot of additional scrutiny. Mycobacterium avium and the other non-tuberculous mycobacteria are ubiquitous," he says.
"For healthy people, they don't represent a significant pathogen," he says. "For the immunocompromised, he says, they are more of a concern. Still, he says, more study is needed to see if the findings have importance clinically and would warrant new advice to people.
Meanwhile? "Cleaning the showerhead is a reasonable thing to do."