A recent study reported that in some communities people regularly shower with a dangerous microbe called Mycobacterium avium — a cousin of the tuberculosis-causing bacteria and one that is quite infectious in its own right.
The University of Colorado-Boulder study is part of a larger research project focused on bacteria we’re exposed to in daily life. This particular study examined showerheads because they provide ideal conditions for the formation of slimy biofilms — an assemblage of bacteria that attach themselves to a surface and excrete a protective mesh layer around themselves (dental plaque is an example), making them difficult to eradicate. Theorizing that the shower might be the point of entry for this infection, lead researcher Leah Feazel told me that researchers collected samples from the insides of 45 showerheads in nine US cities one, two or three times over two and one-half years. They found M. avium in both Denver and New York showerheads.
Confirming the finding, small amounts of M. avium were also detected in the water systems in both Denver and New York City. In those cities, the concentration of Mycobacteria (of which M. avium is one species) in some showerheads was more than 100 times that in the background water. Researchers theorize that this happened because the biofilms were able to establish colonies of such significant size that they could not be dislodged even by water regularly flowing through. Both municipalities treat their water systems with chlorine, ostensibly to eradicate such dangers, but M. avium are known to be resistant, so the bacteria that survive become even stronger. Since many species of Mycobacteria have been implicated in respiratory and other kinds of infections, this is a cause for concern.
M. avium is common in soil and water, but it’s especially dangerous in showerheads because it is dispersed in aerosol form, which is inhaled and can travel deep into the lungs. Like its relative, Mycobacterium tuberculosis, M. avium primarily causes lung disease, but it has also been known to cause digestive and lymphatic system infections. According to Feazel, M. avium infections are rare in people with healthy immune systems and “fairly rare” among the immune-compromised — but they’re on the rise here in the US as well as in the rest of the developed world. The infections caused by M. avium can lead to especially severe illness for people with compromised immune systems, often requiring antibiotic treatment that may be only marginally effective.
Since M. avium is so difficult to kill, individuals known to be immune deficient — including pregnant women… people with asthma or bronchitis… those who’ve had an organ transplant… and those with cancer or other chronic disease — should ask their doctors whether they should bathe instead of showering. Alternatively, Feazel suggests that people with compromised immune systems would do well to change their showerheads every six months (researchers found no M. avium in showerheads less than six months old) and to choose metal ones, which are less hospitable to biofilms than plastic.
