Recent study points to showerheads as bacterial breeding ground

Taking a shower can provide a bracing wake-up call or settle the nerves after a hectic day. But a new study from the University of Colorado, which suggests that the typical showerhead can be an ideal breeding ground for bacteria commonly found in municipal water supplies, might give you pause the next time you step into the shower. The study, " Opportunistic Pathogens Enriched in Showerhead Biofilms," appeared in a recent online edition of the Proceedings of the National Academy of Sciences.

Begun as a class project, the study expanded to include 45 sites in nine metropolitan areas, including New York, Chicago, and Denver. Through the very DNA of the pathogens lodged in the nooks and crannies of about 50 showerheads, researchers identified numerous bacteria, notably Mycobacterium avium , a relative of the organism that causes tuberculosis (PDF).

Bacteria found in showerheads tend to clump together in slimy biofilms, the so-called soap scum that builds up on the showerhead's plastic components, explained Norman R. Pace, Ph.D., lead study author and a professor of microbiology at the university. When a shower is on, pathogens accompany the water droplets that become suspended in the air. Besides coating the shower-curtain liner or walls of the shower enclosure, these droplets are easily inhaled deeply into the lungs.

M. avium, often present in soil, is among a class of nontuberculous mycobacteria, or NTM, described as "ubiquitous" by the U.S. Centers for Disease Control and Prevention. But although M. avium accounts for most known infections by NTM, M. avium has not been well documented as a source of infection since suspected cases of NTM infection don't have to be reported to the CDC.

What's certain is that, while M. avium complex, or MAC, is unlikely to affect most people, if contracted it could potentially cause pulmonary disease, with symptoms similar to those of tuberculosis, including a chronic shallow cough, fever, fatigue, and weight loss. Most at risk, however, are those with compromised immune systems, including people with cystic fibrosis or AIDS or who are elderly, pregnant, or otherwise immune compromised.

The study focused on showerheads, but your home has other potential hot spots, such as a humidifier not cleaned thoroughly, hot tubs, and food-prep areas. Even indoor air carries bacteria, but municipal tap water has 10 times the amount commonly found in indoor air before it even reaches the showerhead. And there's no proof that raising the temperature of your water heater would make a significant difference; the culprit is continuous moisture.

Whether or not you're especially at risk, here's what you can do to try to prevent any bacterial problems in the shower:
• Before showering, run hot water in the shower for a minute or two. Keeping the curtain or enclosure door open during this period might also diminish the concentration of the initial eruption of suspended droplets. Note that you would end up using more hot water this way, unless you shorten your actual shower time to compensate.

• Drain as much water as possible from the showerhead, perhaps even shaking out a handheld model, once everyone is done showering for the day. This gives any bacteria less of a medium to flourish. Some manufacturers claim their showerheads are self-draining after use, but we have not tested the claim.

• Periodically remove the showerhead and clean it in boiling water or with chlorine bleach or ammonia or another cleanser. (Caution: Never combine a product that contains chlorine bleach with one that has ammonia, as that mixture can cause a very hazardous reaction.) The cleaning could destroy any bacteria growing in the showerhead if you're concerned. Note that the bacteria will return and that cleaning is not a surefire way to kill bacteria. M. gordonae, another bacterium prominent in the showerheads discussed in the University of Colorado study, actually grew threefold after treatment with bleach.

• If someone in the household is immune compromised, substitute the usual showerhead with one that's all metal inside and out; the study researchers say such a model should reduce bacterial growth.

But it could be hard to find a showerhead without some nonmetal materials inside the head. Manufacturers we contacted said that not only would all-metal showerheads be extremely heavy and expensive but also that the various settings and streams available in today's models would not be possible using only metal. Even heads with metal exteriors typically need rubber gaskets and plastic flow restrictors inside to comply with state and national water-use regulations.—Ed Perratore | e-mail | Twitter | Forums | Facebook

Essential information: The models in our latest report on showerheads recently tested ( ratings available to subscribers) all include some plastic parts.