What's Hiding In Your Showerhead?

A new study says showerheads may harbor microbes that can be harmful to people with compromised immunity. Biologist Norman Pace describes what his lab found growing inside some showerheads, and explains how shower spray may help the organisms spread.

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IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow.

(Soundbite of music)

FLATOW: The next time you step into a shower, beware, beware not of Norman Bates but of a different kind of danger. According to a new study, your showerhead may be harboring a film of potentially dangerous microbes. Scientists from the University of Colorado Boulder swabbed the insides of 45 showerheads, including the teeming metropolis that is New York and the Rocky Mountain high of Denver, and what they found has a big yuck factor because growing inside some of the showerheads were films of bacteria, a Petri dish of organisms, including a potentially harmful relative of the bug that causes tuberculosis.

Joining me now to talk more about it is Norman Pace, a professor of molecular, cellular and developmental biology at the University of Colorado in Boulder. Thanks for joining us, Dr. Pace.

Dr. NORMAN PACE (Professor of Molecular, Cellular and Developmental Biology, University of Colorado in Boulder): Delighted, thank you.

FLATOW: You don't have to be named Norman, I don't think, to be in a shower anymore.

(Soundbite of laughter)

Dr. PACE: Good idea.

FLATOW: Good idea. Give us an idea. You looked for bacteria growing in the showerheads. So tell us what you found?

Dr. PACE: Well, this is part of a much larger project, to study the microbiology of the indoor environment. We don't think much about it, but as we humans move around our daily activities, that we're actually moving through a suspension of bacteria, and we know little about that. And the goal of this particular study, supported by the Alfred P. Sloan Foundation, is to understand the microbiology of the indoor environment.

FLATOW: And did you find any potentially harmful ones there?

Dr. PACE: Well, the showerhead story was, again, a small part of a much larger story. And in this particular case, we were trying to focus on areas that we knew that potential pathogens occur, which could occur in such a way as to increase exposure to otherwise organisms that you might not be exposed to.

FLATOW: And you found some.

Dr. PACE: And the specific organism that we encountered at high levels in many showerheads was of concern. It's an organism by the name of Mycobacterium avium. It's one of a collection of closely related organisms that, among other things, cause serious pulmonary disease.

FLATOW: So that doesn't mean, though, when I take a shower I'm going to get some lung disease.

Dr. PACE: Well, not necessarily. So there are two issues. One, there's the microorganisms that accumulate in the showerhead, and the other issue is the microorganisms that come in with the municipal waters. And so what we found is that the organisms that form bio-films inside showerheads are a subset of the organisms that are fed in through the municipal waters, but particularly whereas Mycobacterium avium occurs at, oh, say .1 to 1 percent of total bacteria in the municipal waters that you would detect, in the case of showerheads, they could be up to 70 or 80 percent of what's there, namely a 100-fold enrichment of the background microbiology.

Now the large issue, the large issue, however, is this microbiology is always around. These organisms are called opportunistic pathogens, in the sense that they're always around but yet can't infect you. And the real issue with showers is the mode in which the organisms are delivered, and there is the issue because showers generate aerosols. Many aerosol particles are very small, 20 micrometers or less in diameter, and they can penetrate the deep airwaves, carrying along a bacteria that happened to be there for the ride - i.e., those that wash out of showerheads or just happen to come out through the municipal water.

FLATOW: And so the chlorine in your water system doesn't kill these bacteria.

Dr. PACE: Well, even a little bit worse, the chlorine in the water system actually selects for microbacteria because they tend to be fairly resistant to chlorine. And so whereas the chlorine knocks off many of the organisms, the Mycobacterium avium it perhaps slows down but certainly doesn't restrict development.

FLATOW: So whereas these bacteria may be living all around us in the soil and other places and may not be harmful to us, what I'm hearing you say is that when they're made into an aerosol, and they're sprayed, and we inhale it deeply into our lungs, that's where the problem may result.

Dr. PACE: That's the problem, and that's the specific problem. The organisms are always there. They're present in greater or lesser concentrations, but the issue is one of are they delivered to a place where disease can result, and the shower aerosols are a good shot for that.

FLATOW: So if you come down with a cough, let's say, and you go to your doctor, and he looks at you, and he says, well, it may be TB or something, and I'll do tests for all those things, and I don't find anything. And you say, but I'm still coughing, he or she may not be testing for the right thing.

Dr. PACE: That's correct. Mycobacterium avium disease, pulmonary disease, is a - we're just seeing the tip of the iceberg in terms of diagnostics in this country. The is that Mycobacterium avium pulmonary disease is not a communicable disease. You don't catch it from human to human, you catch it from exposure to the environment. And so therefore, it's not considered a communicable disease by the CDC, Communicable Diseases Center, and so there's not even records, national records, on the occurrence of Mycobacterium avium. But there's general agreement that it far outweighs Mycobacterium tuberculosis in this country at this time.

FLATOW: And it's far less deadly?

Dr. PACE: Well…

FLATOW: We don't know.

Dr. PACE: We don't - I think it just chews away at your lungs, much like tuberculosis does. And so it's another - it's a disease also which probably accumulates over the course of years before you ever seek therapy.

FLATOW: So if you really wanted to be proactive, you should be speaking to your doctor about testing for that.

Dr. PACE: Yes, if there is concern, and what means concern? Well, what that means is a low-grade cough that persists for months, you feel lousy, weak, perhaps breathing difficulties, particularly when exerting. Yes, that's a good reason to finger the possibility of Mycobacterium avium pulmonary disease. It's very under-diagnosed.

FLATOW: It's very interesting. 1-800-989-8255 is our number. Is there anything we can do to disinfect our showerheads, if we…?

Dr. PACE: Well, you can disinfect your showerhead, and you might kill everything in there for a while or, you know, momentarily, but the fact is that inocula are continuously being loaded in from the municipal water coming into the showerhead. And it's a dark, moist place, and that's a nice place for the organisms to grow. And it turns out that Mycobacterium avium, the properties of that organism are particularly disposed to formation of very tough bio-films.

FLATOW: You know, there are so many different kinds of showerheads. There are metal ones, plastic ones. Are any of them better at resisting the bacteria?

Dr. PACE: Well, we have no hard information on that. We have only anecdotal information. And what that means is that our approach to sampling the showerheads was to take the showerhead off and swab it out. And if you have a plastic showerhead, it oftentimes will look a lot worse than a metal showerhead in terms of the bio-film load, and also, we tend to get a lot more DNA out of plastic showerheads than we do out of metal showerheads.

So our hip-shot conclusion at this stage of the game is that use of metal showerheads is probably a very good thing to do compared to plastic showerheads. And I would even extend that into household piping. A lot of metal piping is being replaced with plastic these days, and I don't think that's necessarily a good thing because the plastics will load up more readily than metal. Now, not all plastics load up more, but the kinds of plastics that are used for bathroom facilities, they do.

FLATOW: We have a Tweet from Olliex(ph) that came in. It says: What about municipal water versus well water versus rainwater, different kinds of water?

Dr. PACE: Yeah, well, we looked at municipal-water-supplied showerheads and a few, four only, well-water-supplied showerheads, and we saw no Mycobacterium avium in well-water-supplied showerheads. We could detect Mycobacterium in more than 80 percent of showerheads fed by municipal waters.

FLATOW: Wow. Let's see if we can get a quick call in here. David(ph) in Denver. Hi, David.

DAVID (Caller): Hi, thanks for taking my call. I'm a person living with HIV infection, and I've been living with HIV for over - well, almost 28 years at this point - from blood transfusions in 1981. And in the HIV/AIDS community, we're familiar with Mycobacterium avium complex, which, generally speaking, doesn't become a problem for human immunology until one is below 100 T4 cells. They're called helper cells, and at that point, we begin to consider, in the HIV clinical treatment, the taking of Mycobacterium avium complex prophylaxis, specifically drugs like Azithromycin, an antibiotic.

And so I'm wondering to what degree, for persons with normal immunology, which clearly I'm not one of those persons, and nor would persons who are undergoing cancer chemotherapy, but for persons of normal immunology, to what extent is the emergence of Mycobacterium avium in showerheads, for example, a broad - a widespread problem?

Dr. PACE: Well, one problem is that whether taking any particular shower is problematic, you never know, of course. Mycobacterium avium, or you use the term Mycobacterium avium complex, which is a good one to use because there are several organisms that fall into that particular bailiwick, that is they're all very closely related organisms. Other examples of these organisms would be, beyond Mycobacterium avium, would be Mycobacterium intracellulare, for example, you know, very close relatives of one another.

So for a person with a normal immune response, I would say that probably there's no particular threat. The problem that arises, however, is that Mycobacterium avium disease, or MAC disease, Mycobacterium avium complex disease, is insidious. It can persist at low grade for many, many years. And then, and only then, become a problem. And again, the disease may be very well-developed before the symptoms are manifest, and that can be a problem.

I think in the case of individuals who are of normal constitution and not elderly or not drug-addicted or not HIV-infected or the many cases of immune compromise that one can site, I think that if one is not particularly compromised, there's not a particular problem. If, however, there is compromise, which you may not even be aware of at any given time, then there's an issue.

FLATOW: So be aware of the possibility of this.

Dr. PACE: Yeah, I think be aware of the possibility. And you know what I think that the real issue is, is the aerosols that are generated by the shower. If one is concerned, the straightforward thing to do is to take a bath instead of a shower because a bath doesn't have the aerosol-generating qualities that the shower has.

FLATOW: So you shouldn't worry about swimming pools, either, then?

Dr. PACE: Well, that's another issue. That's another study that we have underway, of therapeutic and public swimming pools, and Mycobacterium avium, MAC, is an issue in those particular settings.

FLATOW: We'll have you back to talk about that. Is that something undergoing now?

Dr. PACE: It's underway right now. That study - underway right now, correct.

FLATOW: So take it - if you think you're compromised, and you're worried about it, take a bath.

Dr. PACE: Take a bath or stop using a showerhead and just hook a straight hose up to your shower, the showerhead. Instead of the showerhead, just plug a hose onto the water outlet that would normally feed into the showerhead and take a hose bath instead of a shower bath.

FLATOW: All right, well, we'll have you back when your swimming pool study is finished.

Dr. PACE: Okay, sounds fine.

FLATOW: Sounds quite interesting. Dr. Pace, thank you for joining us.

Dr. PACE: My pleasure, thank you.

FLATOW: Norman Pace, professor of molecular, cellular and developmental biology at the University of Colorado in Boulder.

We're going to take a break and switch gears. Our number, 1-800-989-8255, and talk about a junior T. rex, a tiny T. rex, which I guess it's not really a T. rex. We'll have to call it something else, right? We'll talk about what it is. Stay with us. We'll be right back after this break.

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