Our daily shower doesn’t just contain water; we can also get a face full of bacteria too. Shower heads can expose people to microbes, including potentially harmful pathogens according to research published this week by Pace (from the University of Colorado at Boulder) and colleagues.
Microbes (like bacteria, fungi and viruses) are everywhere and we humans interact with them on a daily basis. Most of the time, these microbes are harmless but sometimes they can cause disease. Shower heads are dark, warm and moist and can be the perfect breeding ground for bacteria. Bacteria multiply and clump together to form a biofilm (a slimy layer of bacteria stuck together). Our daily shower sprays these bacteria in tiny droplets of water (aerosols) into the air. Bacterial aerosols can be inhaled deep into the lungs and can cause diseases like bronchitis and other lung infections. This is a particular problem in immunocompromised individuals (people with a weak immune system that cannot fight off infections well) who are susceptible to infections by opportunistic pathogens (pathogens that usually do not cause disease in healthy people).
Shower heads have been implicated as a source of disease-causing pathogens such as Legionella pneumophila (the bacteria that causes Legionnaire’s disease) and Mycobacterium avium (M. avium, which can cause symptoms ranging from a mild persistent cough in healthy people to a tuberculosis-like disease in the immunocompromised). However, very little is known about what bacteria are present in shower heads and how frequently they can occur. This study aimed to look at the different types of bacteria that can be found in shower heads across several cities in the United States.
The researchers took swabs from 45 shower heads in homes, apartment buildings and public places in several sites in the United States; including New York City, Denver, Southern Colorado and Tennessee. They also took samples of the water that flows through the shower head. It can be very difficult to isolate bacteria from the environment and then grow them in the laboratory so the researchers used molecular genetics techniques to identify the bacteria. Bacterial DNA was isolated from the shower head swabs and water samples. The DNA was then amplified using polymerase chain reaction (PCR) to make thousands of copies of a particular bacterial gene. This gene was then sequenced to reveal what bacteria are present in the samples. Additionally, the researchers analysed samples using a very sensitive PCR reaction called quantitative PCR to specifically detect a single species of bacteria, M. avium.
The researchers found many different species of bacteria (including Mycobacterium, Escherichia and Methylobacterium species) on the shower heads which varied across the different sites. Many of the bacteria identified were common bacteria that are normally found in soil and water and are present everywhere, such as Pseudomonas and Sphingomonas species. Interestingly, there were more Mycobacterium species found in shower heads than in the tap water. Shower heads contained levels of M. avium that were >100 times higher than in the tap water supply and 20% of shower heads in the study were found to contain M. avium. Interestingly, the more publicised L. pneumophila, the cause of Legionnaire’s disease, was rarely identified in the study.
There’s no need to panic the organisms found in this study are not harmful to healthy people. M. avium is a bacterium that is commonly found in soil so we can easily encounter it in other settings within our daily lives, not just showers. The presence of M. avium in shower heads is only a concern because shower heads could create aerosols of bacteria that can be easily breathed directly into our lungs. Don’t forget M. avium only causes a mild infection in healthy people, and most people don’t even get symptoms. More serious infections are only seen in people with already weakened immune systems such as those with AIDS or cystic fibrosis. Also, M. avium was not isolated everywhere, it was only found in certain sites across New York and Denver.
Professor Pace recommends “avoiding showers” for those who are immunocompromised if you want to reduce your risk of exposure to bacterial aerosols. He also suggests replacing shower heads more regularly, especially with metal ones since plastic ones “load up” with bacteria more quickly.
Ultimately your shower isn’t likely to make you sick and this is just an interesting study that describes some of the bacteria we encounter in our everyday lives. It gives an insight into the ecology of certain environments within the home, in this case what lurks beneath your shower head.
This work was published on 14th September 2009 in the early edition of the journal PNAS (Proceedings of the National Academy of Sciences).