Bug alert

New Delhi, Sept. 14: Shower baths may inject harmful bacteria into human lungs, according to scientists who have identified a risk associated with showerheads that makes bucket-and-tumbler baths appear safer.

A study by US researchers has shown that showerheads harbour vast colonies of bacteria that cling to the outlet zones, creating thin mats of microbes called biofilms, despite the chlorination of water and the force of water.

The study, published today in the Proceedings of the National Academy of Sciences, suggests that bacteria from such biofilms on showerhead surfaces may be delivered as aerosols that may be inhaled during shower baths.

“Showering creates tiny particles that can be inhaled deep into the lungs — and if these particles contain pathogenic (disease-causing) bacteria, disease may result,” said Leah Feazel, a research team member at the University of Colorado, Boulder.

Earlier research two years ago had shown that bacteria can lurk on showerheads. The new study is the first to investigate and characterise the composition of the microbes that live there. Feazel and her colleagues sampled 45 showerheads from nine cities in the US and used a technique that screens DNA, or genetic material, to determine the composition of the bacteria.

The study revealed significant levels of Mycobacterium avium, a bacteria known to cause lung disease similar to tuberculosis in persons who are susceptible or who have weakened immune systems, in nearly one-third of the showerheads.

Smoking, chronic lung disease and alcoholism are among risk factors that make people susceptible to lung infection with Mycobacterium avium which can cause chronic shallow cough, fever, fatigue and weight loss.

While any source of standing water is a likely spot for bacterial growth, the unique architecture of showerhead interiors allows bacteria from water to cluster along the surface as biofilms where the concentration of bacteria may be 100 times higher than in water. Researchers say bucket-and-tumbler bathing is likely to be safer for people at risk of developing lung infections.

'The bucket-and-tumbler method likely does not create water droplets of a size that can be deeply inhaled and thus could reduce the risk of a lung infection,' Feazel told The Telegraph in an interview.

Faucets produce fewer aerosols and thus reduce the risk of inhaling aerosols. 'In the US and in Europe, we recommend at-risk persons take baths which also result in large (safe) water droplets,' Feazel said.

The microbial load in showerhead biofilms may be higher in countries where the water is less clean, said Norman Pace, professor of molecular biology at the University of Colorado and the study leader.

The researchers caution that their findings should not be interpreted to suggest that showers are dangerous for all. 'For the average person, showers are fine,' said Laura Baumgartner, another team member.

However, the use of showers may be inadvisable for persons with compromised lung conditions or compromised immune systems.

For persons who cannot avoid showers, said Baumgartner, it may be a good idea to avoid the first flow of shower water. 'It's possible that the first spray has the highest load of microorganisms - but this is still a hypothesis,' she said.

The showerhead study is part of a larger effort to examine the microbiology of the human environment in homes, schools and public buildings, using a technique that allows researchers to identify organisms that humans encounter every day.

The reasons for the clustering of mycobacterium through biofilms in showerheads is still unclear, but the waxy quality of these germs and their resistance to chlorine as well as the force of the ejected water during shower baths allow them to accumulate.

The study showed that bleach doesn't clear microbes. In one experiment, the Colorado team found that several months after bleach treatment, the concentration of a species of mycobacteria had increased three times.

The microbes attach more easily to plastic than metal. 'Metal showerheads may be a good alternative,' said Norman Pace, research team leader, in a statement issued through the University of Colorado.