"Modern molecular methods can reveal abundant airborne microbes where conventional culture methods used to assess cleanliness do not, say
researchers. Their conclusion is based on a study of a hospital therapy pool which made nine lifeguards sick.
The team is now calling for the use of the molecular techniques to ensure safety in healthcare, describing existing methods as "seriously
The workers tending the warm indoor pool at a hospital in the US Midwest fell ill in 2000 with an occupational lung disease resembling pneumonia
called hypersensitivity pneumonitis. Culturing samples from the workers revealed the culprit to be a bacterium called Mycobacterium avium.
The pool was equipped with a "state-of-the-art" disinfection system but the incident prompted Largus Angenent, at Washington University in St Louis,
US, and colleagues to survey the bugs present in the pool and its surroundings using molecular techniques.
Bugs on plates
Angenent says airborne microbes are particularly hard to identify using traditional culture techniques, which involve growing bugs on agar plates in
the lab. "If something has been aerosolised it's really hard to grow - or even if it's not, only 1% of soil organisms can be grown in the lab," he
This means that when healthcare organisations test for contamination, they "are really only going after a small percentage of organisms", says
Angenent. "The approach we took goes after everything."
He believes the results of the study will reflect the situation in other hospital pools and in private hot tubs. "I don't want people to start
panicking, but we need to be aware of what's really there - and not base everything on culture studies," he told New Scientist. The molecular
technique the team used samples the germs' DNA.
The researchers tested the pool water, the film on the pool walls and the air above the pool. A sterile filter was used to take a sample and then DNA
was extracted and tested for a particular gene that is present in all life forms. This gene codes for a section of ribosomal RNA (called 16s) that has
changed little through evolution.
Angenent and colleagues amplified the different forms of the gene they found, each of which represented a different strain of organism.
A drawback of this molecular approach is that it does not reveal whether a bug can infect a human. But for certain conditions - such as
hypersensitivity pneumonitis - this is irrelevant as the symptoms are caused simply by a biological reaction to the presence of the bug in the
The new study also found relatively greater numbers of certain bacteria, called Gram positive bacteria, in the warm air above the pool than in the
water itself. Ironically, these bacteria, including Mycobacterium, can be inadvertently amplified by disinfecting systems.
Angenent explains that such bacteria have very waxy cell coats which makes them resistant to disinfectants such as chlorine or hydrogen peroxide in
pools. "What can happen is that we kill everything else except these very resistant organisms. And then they have no competition," he told New
For years CDC has known that hospitals were very vunerable to airborne pathogens, the "design" of hospitals ignores airborne cross contamination
except for very high level labs. The old saying that hospitals is "where" I got sick has some basis in truth.