COMMENTARY

Are Showerheads Causing Chronic Lung Infections?

Paul G. Auwaerter, MD

Disclosures

December 17, 2018

Hello. This is Paul Auwaerter, speaking for Medscape Infectious Diseases and from the Johns Hopkins Division of Infectious Diseases. Like many of my infectious diseases colleagues, I often take care of people in the older age range who suffer from bronchiectasis and nontuberculous mycobacterial (NTM) infections. These are often quite challenging patients in terms of management and deciding whether to embark on long-term antibiotic therapy. One of the most frequent questions I am asked is how to prevent these infections from happening.

NTM are very prevalent in the environment—in soil and water. They live in amoebae and can be found in dust, and are more commonly identified environmentally in some areas than others. Almost 10 years ago, a group published a paper in Proceedings of the National Academy of Sciences (PNAS)[1] that identified NTM in showerhead biofilms 100 times more commonly than in background water. This raises the specter that showerheads and other water sources that have biofilms might be spraying aerosolized NTM. This wouldn't cause problems for most people, but in those who are susceptible, this might cause an infection.

Of course, this is just a hypothesis currently, but additional investigators have followed up on it, including a group[2] who recently asked for showerhead samples from citizen scientists across both the United States and Europe. From those samples, NTM were quite prevalent. Most commonly found was Mycobacterium gordonae—the so-called "tap water bacillus," which was perhaps no surprise, and we tend to discount that. They also found Mycobacterium mucogenicum. But number three came in as Mycobacterium avium intracellulare—the one that tends to be the most common cause of NTM lung disease, especially in older people.

This study also reflected a correlation with geographic NTM hotspots, and investigators have surmised that perhaps this could account for why there's been an increasing prevalence. They also found that municipal water supplies were more likely to harbor such organisms compared with private well-water supplies. It appears that chlorine and chlorine-like compounds don't kill NTM quite as well, and there are different pH and water-supply issues in Europe that may make NTM species less prone to growth there.

This is interesting. Patients ask, "Should I shower or not?" I typically say that it's hard to avoid, but perhaps if there is high biofilm density, it does make some sense to bathe, especially if you don't mind taking a long, hot, and relaxing bath, which isn't as quick as a shower. But for susceptible people it may be helpful as a behavioral change, especially since we have few other ways [to prevent NTM infections.]

One of the investigators from the MBio study, Rob Dunn, wrote a very interesting book called Never Home Alone (Basic Books, 2018) that expands on some of the microbiome issues that are certainly hot topics in terms of our bowel and skin flora, etc. This is a look at the home environment where we have insects, mice, fungi, and other organisms. Much like the hygiene hypothesis (in which people might have more autoimmune disease and allergies because we're really too clean), they make the argument that there might be some balance to having all of these environmental organisms in our households. They even make the point that research has shown that mice exposed to NTM tend to be less anxious and appear calmer, perhaps because of increased serotonin levels. So perhaps everyone shouldn't try to eradicate the NTM from their showerheads. Who knows?

NTM are increasing in prevalence. They've received a closer investigation and deserve a lot of attention. They are more common here in the United States than tuberculosis. So stay tuned. I know some organizations, such as the Cystic Fibrosis Foundation, are very interested, because many of those patients are affected. And with an aging population, this will deserve more attention. Thanks very much for listening.

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