Exophiala: understanding the risks and
protecting vulnerable groups
This leaflet has been put together to provide background information on Exophiala
dermatitidis and Exophiala phaeomuriformisin. This briefing material has been
produced for those who work in the healthcare professions, the media and others
who are looking for some background understanding of hygiene issues related to
Exophiala and/or those who are responsible for providing guidance to the public on
coping with hygiene issues associated with Exophiala.
In June 2011, headlines such as “Dishwashers harbour killer bugs” and “my
dishwasher is trying to kill me” appeared in the media. This represents another
example of overhyping and scaremongering by the media. The reports were based
on a newly published study1 that investigated the rubber sealing on the doors of
domestic dishwashers, and found Exophiala dermatitidis and Exophiala
phaeomuriformisin in around 30% of 189 domestic dishwashers sampled in multiple
locations across the world. Although the organism is known to be an opportunist
pathogen, no incidents of infection from dishwashers were reported.
Headlines like these are very confusing to the public, who have to try and grasp what
are the real infection risks to themselves and their families. In 2009 we had the
influenza pandemic, where the risks of person-to-person transmission were very
high, and health authorities were stressing the need for good respiratory hygiene to
mitigate spread whilst vaccines were developed. In the last month we have had
Escherichia coli O104, where we have had to try and convey to the public, that
although the risks of spread are relatively less than for flu, and most cases have
come from eating contaminated sprouts, several cases of transmission from an
infected person to another family member (or to people for whom the infected person
prepared food) dictated a need to stress good hygiene for close contacts of those
who are infected. Using the words “killer” and deadly” in association with Exophiala
as well as E. coli and flu is very misleading.
Although the risk may seem to be small, and no infections have been reported, what
the researchers, quite rightly, say is “the potential hazard they represent should not
be overlooked”. This is just another example of how changing lifestyles, new
technology, our efforts to reduce water, power, biocide etc. usage, and so on can
“throw up” infectious disease risks, which we could not have necessarily predicted.
Microbes are evolving all the time to adapt to new environments that can lead to new
infectious disease risks. The most important examples are Legionnaires’ disease,
whereby blowing cold air over water (where the legionnaires’ bacillus naturally
occurs) leads to aerosolisation of the bacillus which, when inhaled, can cause
respiratory infection particular in risk groups (e.g. a legionnaires’ reunion in a US
hotel). Another example is Listeria, which is adapted to grow at the very low
temperatures of open freezer cabinets. This means that we need to always be
prepared for the unexpected, and to assess the implications of new published data
that might suggest hitherto unrecognised infection risks.
What is Exophiala?
Exophiala is a fungus widely distributed in soil, plants, water, and decaying wood
material. As well as being a saprophyte in nature, it is the causative agent of various
human infections. Exophila spp. are initially yeast-like, moist, and brownish to
greenish black in colour. The texture of the colony eventually becomes velvety due to
development of short, aerial grayish hyphae. The genus contains 28 species.
Exophiala dermatitidis is a slow-growing fungal pathogen of humans that exists
predominantly as a yeast form in vitro but can be manipulated to undergo
morphological transitions to multicellular forms and various types of hyphae. This
species is known to occur in the environment, but is practically absent from dead
plant material or soil, and has never been reported from outdoor air. The somewhat
odd spectrum of main sources of isolation (fruit surfaces, steam baths, faeces, and
human tissue) suggests that a hitherto unknown, quite specific natural niche must be
concerned. Consistent occurrence in steam rooms of public bathing facilities
suggests that the artificial environment of the steam bath provides a novel
environmental opportunity for this fungus.
Both Exophiala species are known to be able to cause systemic disease in humans
and frequently colonise the lungs of patients with cystic fibrosis. The black yeast
Exophiala dermatitidis is also an uncommon aetiologic agent of fatal infections of the
central nervous system in otherwise healthy, mainly adolescent patients in East
Asia.2 In the US, cases have been reported where inoculation of patients with
medical fluids containing contaminated water led to common-source outbreaks with
sometimes fatal neurological implications. More frequently, asymptomatic
colonisation is observed in protected body sites, e.g. in the mucus of lungs in 2-8 %
of patients with cystic fibrosis (CF), in the intestinal tract in 0.3 % of the European
population and occasionally in the wax of human external ear canals.
Importantly, however, it is stated the route of infection is unknown i.e. there is no
evidence that oral consumption can lead to infection.
What are the risks of Exophiala infections from contaminated dishwashers?
The reports were based on a newly published study that investigated the rubber
sealing on the doors of domestic dishwashers and found Exophiala dermatitidis and
Exophiala phaeomuriformisin in around 30% of 189 domestic dishwashers sampled
in multiple locations across the world. The authors verbally reported that they had
also found the organism on plates and cutlery taken from the dishwashers.
Since there is very little known about the organism and its properties in domestic
environments (which is very little), it is impossible to assess the extent of the risk (in
the way we have been able to do for e.g. hands or laundry) but it seems likely to be
very small, and then only to “at risk” groups e.g. cystic fibrosis patients.
Hygiene advice for those caring for children and others with cystic fibrosis
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The following advice should be given to those caring for children or others who have
cystic fibrosis:
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At least once a week, use a high temperature (60°C) wash with detergent on
an empty cycle to prevent the build-up of fungi in the dishwasher − and also
the washing machine.
Regularly disinfect the rubber seals of the dishwasher and washing machines.
Make sure you use a disinfectant or disinfectant/cleaner such as a bleachbased product, which is active against Exophiala species. For bleach
(hypochlorite) products, use a solution of bleach, diluted to 0.5%w/v or
5000ppm available chlorine. Household bleach (both thick and thin bleach) for
domestic use typically contains 4.5 to 5.0%w/v (45,000-50,000 ppm) available
chlorine. Bleach/cleaner formulations (e.g. sprays) are formulated to be used
“neat” (i.e. without dilution). It is always advisable, however, to check the label
as concentrations and directions for use can vary from one formulation to
another.
In March 2011, Kondori et al reported on a study of E. dermatitidis in respiratory
specimens from cystic fibrosis (CF) patients, transplant recipients, and subjects with
other respiratory disorders in Sweden.3 Sputum and bronchoalveolar samples derived
from 275 patients were investigated. E. dermatitidis was isolated in respiratory
specimens from 19% (18/97) of the CF patients but in none of the other patient
categories. Although Exophiala dermatitidis is considered to be a harmless coloniser
of the airways of CF patients, in some patients, pancreatic insufficiency was positively
associated with the presence of E. dermatitidis suggesting that E. dermatitidis
colonisation of the respiratory tract in CF patients may be associated with more
advanced disease.
Why should we take the new research reports seriously?
Although the risk from dishwashers contaminated with Exophiala spp. may be small,
as the authors say, the potential hazard they represent should not be overlooked.
This is just another example of how changing lifestyles, new technology, our efforts
to reduce water, power, biocide etc. usage, can “throw up” infectious disease risks.
Microbes are evolving all the time to adapt to new environments, this can lead to
hitherto unrecognised infectious disease risks.
This research on dishwashers is part of a much larger piece of research assessing
how the extreme environment created in the home, and in home appliances can
encourage the emergence of “extremophiles”, and that these emerging stresstolerant species may have increased human pathogenicity. In the conclusions to a
review of this research4 the authors state “Industrialisation has created environments
that can support the growth of only a few adapted microbial species, and thus select
them for traits that might also be important for human pathogenesis. Evolution in
indoor environments is driven by periods of extremely unfavourable conditions (e.g.
low water activity, high temperature) and the presence of unusual growth substrates,
such as silicone rubber and disinfectants. This selects for traits that (i) confer
tolerance to these stress factors, and (ii) can enhance their pathogenicity (make the
organism more likely to cause infection). The numerous opportunities for contact
with, and infection of, humans (most particularly the increasing ageing human
population and immunocompromised individuals in the home) and lifestyles that are
increasingly confined to indoor environments might also increase the risk of
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emergence of new fungal pathogens. While for some traits associated with evolution
of microbes to resist “stress” (e.g. antibiotic resistance) are already widely accepted,
we are still not aware of the other consequences of this evolution that is going on
around us. We might have turned our homes into microcosms for the experimental
evolution of the most resilient of microbial species, the adaptability of which might
enable them to find new niches in the human body.
The authors postulate that wet rooms, such as bathrooms, kitchens and steam baths
in our households tend to harbour fungal biota. They suggest that high temperatures,
high moisture and alkaline pH values due to regular use of detergents, typically
occurring in dishwashers can provide novel niches or habitats for species also known
to be pathogenic to humans. Dishwashers intermittently experience temperatures as
high as 60-80C, high organic loads, high concentrations of salt to prevent calcareous
accumulation and aggressive alkaline detergents. The seals of dishwashers might be
even used as a nutrition source for microorganisms. The high prevalence of the two
Exophiala species in dishwashers can be explained by their remarkable
thermotolerance, halotolerance and pH tolerance, the combination of which has
previously not been observed in fungi. Water hardness also seems to have a role in
the persistence of E. dermatitidis and E. phaeomuriformis in dishwashers. The
majority of isolates of both species were found in medium hard and hard water areas.
In this study active growth for Exophiala was recorded with up to 47°C, in a pH range
between 2.5 and 12.5, and with up to 17% NaCl salinity. The latter is important for
survival of osmotic stress during the dry periods in the dishwasher, as well as during
washing when a high concentration of salt is added to prevent accumulation of
calcareous deposits in the machine.
It must also be borne in mind that, recently, the habitats in these household
appliances have tended to become less extreme and easier to occupy for microbes
due to energy-saving regimens, such as using lower temperatures for washing
clothes and dishes, and the use of less aggressive detergents. The authors conclude
“Knowing that these fungi coinhabit our homes, further research is imperative as only
this could reveal, whether the presence of E. dermatitidis inside our households
poses any threat to human health”.
References
1. Zalar P, Novack M, de Hoog GS, Gunde-Cimerman N. Dishwashers: A man-made
ecological niche accommodating human opportunistic fungal pathogens, Fungal
Biology (2010), doi:10.1016/j.funbio.2011.04.007.
2. Sudhadham M, Sihanonth P, Sivichai S, Chaiyarat R, Dorrestein GM, Menken
SBJ, de Hoog GS. The neurotropic black yeast Exophiala dermatitidis has a possible
origin in the tropical rain forest. Studies in Mycology. 2008;61:145-55.
3. Kondori N, Gilljam M, Lindblad A, Jönsson B, Moore ER, Wennerås C. High rate of
Exophiala dermatitidis recovery in the airways of patients with cystic fibrosis is
associated with pancreatic insufficiency. J Clin Microbiol. 2011 Mar;49(3):1004-9.
Epub 2011 Jan 5.
4. Gostincar C, Grube M, Gunde-Cimerman N. Evolution of Fungal Pathogens in
Domestic Environments? Fungal Biology (2011), doi:10.1016/j.funbio.2011.03.004
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IFH Guidelines and Training Resources on Home Hygiene
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Guidelines for prevention of infection and cross infection the domestic
environment. International Scientific Forum on Home Hygiene. Available from:
http://www.ifh-homehygiene.com/best-practice-care-guideline/guidelinesprevention-infection-and-cross-infection-domestic
Guidelines for prevention of infection and cross infection the domestic
environment: focus on issues in developing countries. International Scientific
Forum on Home Hygiene. Available from: http://www.ifh-homehygiene.org/bestpractice-care-guideline/guidelines-prevention-infection-and-cross-infectiondomestic-0
Recommendations for suitable procedure for use in the domestic environment
(2001). International Scientific Forum on Home Hygiene. http://www.ifhhomehygiene.org/best-practice-care-guideline/recommendations-suitableprocedure-use-domestic-environment-2001
Home hygiene - prevention of infection at home: a training resource for carers
and their trainers. (2003) International Scientific Forum on Home Hygiene.
Available from: http://www.ifh-homehygiene.com/best-practice-training/homehygiene-%E2%80%93-prevention-infection-home-training-resource-carers-andtheir
Home Hygiene in Developing Countries: Prevention of Infection in the Home and
Peridomestic Setting. A training resource for teachers and community health
professionals in developing countries. International Scientific Forum on Home
Hygiene. Available from: www.ifh-homehygiene.org/best-practice-training/homehygiene-developing-countries-prevention-infection-home-and-peri-domestic.
(Also available in Russian, Urdu and Bengali)
This fact sheet was last updated in 2014
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