WEDNESDAY, June 22 (HealthDay News) -- Can a dishwasher be both
an excellent cleaning machine
and an agent for infectious disease? Possibly, according to a
The concern stems from an analysis of 189 household dishwashers
in 101 cities around the world. Sample swabs taken from the rubber
seals around the dishwasher doors revealed that more than six in 10
dishwashers (62 percent) contain some form of fungi, said the study
team from the University of Ljubljana in Slovenia.
What's more, 56 percent of the dishwashers -- installed in homes
in Europe, North and South America, Israel, Africa, Asia, and
Australia -- contained at least one of two different species of
Slow-growing forms of black yeast -- such as
Exophiala dermatitidis and
E. phaeomuriformis -- can cause "systemic disease in humans,"
the authors reported. Black yeast, they added, was the type of
fungi most frequently detected.
"The bottom line is that this pathogenic black yeast species occurs rarely in nature, but in very high numbers in the dishwashers," said study co-author Nina Gunde-Cimerman, from the biology department of the University of Ljubljana.
But do dishwasher pathogens threaten the well-being of healthy
"No," concur a pair of American researchers who did not participate in the investigation.
"Frankly, this is of little or no medical importance," said Dr. Henry F. Chambers, chief of infectious diseases at San Francisco General Hospital. "Now I don't dispute that they found these organisms. But I'm not surprised at all. These are hardy organisms. You go in your shower and you will find microorganisms in your shower. Behind your toilet as well.
"We shouldn't overestimate the importance of these organisms relative to what is already in or on your body," Chambers added. "There are by some accounts 10 times more microorganism cells on or in your body than there are your own cells of your own body. That amounts to thousands of billions. And secondly, nothing they found is able to cause disease in people who are not extremely immunocompromised."
Dr. Philip Tierno, director of clinical microbiology and
immunology at New York University Langone Medical Center, echoed
"We're exposed to large amounts of fungi in everyday life," he observed. "When you consume any kind of dairy product you're likely to come into contact with fungi. There are more fungi -- that is, a mold fungus with spores -- in an ounce or two of cheese than you're likely to get from exposure to a dishwasher. And, in any case, 99 percent of the organisms that we come into contact with on a daily basis are totally innocuous."
The study authors, however, are concerned about that other one
percent. More research is needed, they said, to determine whether
E. dermatitidis in appliances can cause humans harm.
Writing in the current issue of
Fungal Biology, the authors said that the presence of black yeast and similar organisms within the "extreme environment" of a dishwasher was "remarkable," given their harsh exposure to high heat and substantial amounts of detergents, alkaline and salt.
"With the new eco regimes that we all use nowadays (meaning lower temperatures, milder detergents), they thrive," Gunde-Cimerman said. "Not much" can be done to combat it, she added.
The presence of these fungi raise concerns about other humid
indoor environments and water-retaining appliances, the authors
said. They noted that continuous exposure to moisture, high acid
content, high temperatures, and residual organic matter (in
particular, food) are features that dishwashers share in common
with bathrooms, sinks, kitchens, and coffee makers.
Black yeast and similar organisms are "opportunistic invaders,"
the scientists added. This means that individuals with a
compromised immune system are particularly vulnerable.
The authors said that black yeast has been found to colonize the
lungs of cystic fibrosis patients. Similarly, white yeast (also
detected in dishwashers in the study) is a familiar problem in
hospital settings, where it can form a slimy coating around
prosthetics, catheters, and tubing.
Even in extremely immunocompromised people exposed to black
yeast and similar organisms, however, "we're talking about very
rare infections," Chambers said.
For more on infection control, visit the
U.S. National Institutes of Health.