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The removal of carpets in homes in response to asthmatic responses in children or allergen avoidance has been recommended by many medical practitioners. This study looks at an alternative to removal and examines the concentration of airborne fine particulates and indoor fungi in homes undergoing a wet extraction or ‘steam cleaning’ intervention. Initial increases in indoor airborne fine particulates were observed, but this was consistent with higher corresponding outdoor levels. Subsequent to the cleaning intervention, viable indoor fungal levels in the test homes remained below pre intervention levels, whereas fungal levels were wide-ranging in the control homes. Penicillium, Cladosporium, Alternaria, Aspergillus, Botrytis and yeast were the most common and widespread fungal taxa recovered indoors and outdoors. Wet extraction cleaning in conjunction with regular dry vacuuming benefits the indoor environment by maintaining not only established fungal levels indoors but also a stable indoor fungal spora.
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C D Cheong1,*, H G Neumeister-Kemp2 and P W Dingle1
1School of Environmental Science, Murdoch University, Murdoch WA 6150, Australia
2School of Biological Science, Murdoch University, Murdoch WA 6150, Australia
The removal of carpets in homes in response to asthmatic responses in children or allergen
avoidance has been recommended by many medical practitioners. This study looks at an
alternative to removal and examines the concentration of airborne fine particulates and indoor
fungi in homes undergoing a wet extraction or ‘steam cleaning’ intervention. Initial increases
in indoor airborne fine particulates were observed, but this was consistent with higher
corresponding outdoor levels. Subsequent to the cleaning intervention, viable indoor fungal
levels in the test homes remained below pre intervention levels, whereas fungal levels were
wide-ranging in the control homes. Penicillium, Cladosporium, Alternaria, Aspergillus,
Botrytis and yeast were the most common and widespread fungal taxa recovered indoors and
outdoors. Wet extraction cleaning in conjunction with regular dry vacuuming benefits the
indoor environment by maintaining not only established fungal levels indoors but also a stable
indoor fungal spora.
Steam cleaning, carpets, indoor fungi, fine particulates, wet extraction, residential homes,
Soft fabric surfaces such as carpets are commonly found in many residential environments.
They fulfil many important health and social functions; they act as a buffer, sink and filter for
airborne particulates, and can suppress dust and noise, which helps to maintain a comfortable
indoor climate in buildings and homes (Frank et al. 1997, Berry 1993, 1994, 2004).
However, carpets are also one of the most important reservoirs and potential sources of
aeroallergens, pollen, bacteria, fungi, dust mites and other components of dust in residential
domestic environments (Shaughnessy et al. 2002, Kemp et al. 1998, ACGIH 1999, Wickman
et al. 1992). Fungi, bacteria and dust are typically ubiquitous in carpets, but complications
arise with poor carpet cleaning and maintenance and/or water damage incidents. Poor cleaning
and maintenance leads to an accumulation of microbial contaminants, while water damage
incidents provide moisture and nutritional substrates (dust, carpet material, padding/underlay,
glue) for microbial organisms to proliferate to problematic levels (ACGIH 1999). These
organisms may then be re-suspended into the air, during normal everyday activities such as
walking and cleaning.
* Corresponding author email:
Health effects and symptoms such as asthma, hypersensitivity, allergies, infections, upper
respiratory and pulmonary symptoms and skin irritations may be attributed to prolonged
exposure to airborne fungi in residential environments (Dales et al. 1997, Godish et al. 1996,
Brunekreef et al. 1994).
To avoid these and other respiratory problems, many medical practioners often recommend
the removal of carpets and soft furnishings in homes, often in response to asthmatic responses
in children or for dust mite allergen avoidance, or through the perception that carpets cannot
be cleaned properly, to be replaced with hard surfaces like wooden or tiled flooring (Berry
2004, Custovic et al. 2002, Patel and Bush 2000). However, this can add considerable
financial and economic burden to the homeowner and could significantly change the
characteristics of the home. An alternative is to clean and properly maintain the carpets and
soft furnishings in situ (Etkin 1994).
Wet extraction (‘Steam cleaning’)
Proper care and long term maintenance of carpets does not involve dry vacuuming alone. A
major element in the care, revitalisation and maintenance of carpet is conducting ‘dry’ or ‘wet
extraction’ cleaning. The US Carpet and Rug Institute and the Carpet Institute of Australia
recommends that carpets receive regular deep cleaning and be ‘dry’ or ‘wet extraction’
cleaned a minimum of every 12 or 18 months, depending on wear and use (CRI 2004, CIAL
2004). This intervention study investigates the influence of a wet extraction, commonly
known as ‘steam cleaning’, intervention on carpets on indoor fungal levels and composition in
non-mould contaminated residential environments.
Fourteen residential homes were selected for participation in this study. All homes were single
storey, of brick construction, ranging between 2 to 30 years old and were within a 15km
distance from Murdoch University. Specific specification required no tobacco smoking within
the home and for all homes to be carpeted (tufted wool or synthetic).
Cleaning interventions
Nine test homes were randomly assigned in the ‘steam cleaning’ group with the other five
assigned in the ‘control’ group. Homes in the ‘steam cleaning’ group had their entire area of
exposed carpeting, fabric upholstered sofas and participant’s bed, thoroughly dry vacuumed
with a vacuum cleaner (Filter Queen, HMI Industries) meeting the Australian Standard
(AS3733) and equipped with a hospital grade HEPA filtration system, to trap and remove
particulate soil and dust (Standards Australia 1995). The vacuum cleaner was equipped with a
motorised head with rotating brushes to add extra power to the cleaning system (Cheong &
Neumeister-Kemp 2005). Carpets were then professionally ‘steam cleaned’ (wet extraction)
by accredited Australian professional carpet cleaners. Non-toxic, low residue detergents and
warm water were used, in accordance to the carpet manufacturer’s instructions, to suspend
soils and dirt in a solution, which was then extracted with wet vacuuming. Special care was
taken not to over wet the carpets.
Industrial sized air movers (Sahara Turbo Drier Model, Drieaz) were then used to facilitate the
quick drying of the damp materials. Occupants were told to keep off the carpets for 4 hours or
until drying was completed. No specific cleaning interventions were conducted in the ‘control’
group. Homeowners for both the control and test homes maintained their normal household
cleaning practices (vacuuming, dusting, etc) for the duration of the monitoring period.
Monitoring protocol
Baseline monitoring for airborne fungi and other air quality parameters (temperature, relative
humidity, airborne fine particulates [0.02 to 1.0µm]) was conducted before and after the
cleaning interventions in the nine test and five control homes. The homes were monitored four
times during the study period at weeks two, six, ten and fourteen weeks after the initial
baseline monitoring. Outdoor samples were concurrently collected for comparison with indoor
Fungal monitoring was conducted in the bedroom of each participant with N-6 Andersen
multi-hole impactor samplers (Andersen Instruments Inc. Atlanta GA) co-located at a height
of 1-1.5m above the ground, for two minutes at a flow rate of 28.3 L/min (Cheong et al. 2004,
Foarde and Berry 2004, Hyvarinen et al. 1993). Outdoor samples were collected 2m away
from the dwelling to represent outdoor air that may enter the buildings from windows or
Malt extract agar (MEA-DIFCO) and Dichloran 18% Glycerol agar (DG18-Oxoid) were
utilised in side by side sampling in order to enumerate a broad spectrum of fungi. Both media
were amended with Chloramphenicol (Sigma) to limit bacterial growth (Cheong et al. 2004).
Cultures were then incubated (5 days, 22oC ±1oC, 30%RH ±5%), counted and reported as the
number of colony forming units per cubic meter of air (CFU/m3). A subset of samples was
differentiated to determine the fungal profile.
Statistical analysis
Analysis of indoor air quality data collected for this study was performed using the MS Excel
V5.0 Statistical Add-ins Package. Paired t-tests assuming equal variance (P) and α = 0.05 and
ANOVA calculations were performed for analysis of variance. Pearson product moment
correlation analysis was used to investigate possible associations or relationships between the
mean air temperature, relative humidity, particulate matter and total fungal colony forming
In total, one thousand one hundred and eighty six samples of airborne viable fungi were taken
from the nine test homes and the five control homes over the study period beginning mid May
and ending October 2000.
Baseline fungal, fine particulate and air quality levels
The mean baseline indoor fungal levels of the 14 residential homes pre intervention were 344
CFU/m3. Corresponding outdoor fungal levels were measured at 415 CFU/m3. Indoor
conditions included a temperature of 18.90C, 59.6% relative humidity and 1.94 x 10-2
particles/m3 airborne fine particulates. Corresponding outdoor conditions included a mean
temperature of 18.40C, 55.7% relative humidity and 1.6 x 10-2 particles/m3 airborne fine
Steam cleaning intervention
% change in indoor fungal levels compared to pre intervention level
% change
post (2 weeks)
post (6 weeks)
post (10 weeks)
post (14 weeks)
Steam Clean
Figure 1. Percentage change in indoor fungal levels compared to baseline (pre intervention)
levels in steam clean and control homes
Viable indoor fungal levels in the steam clean (test) homes remained below pre intervention
levels, whereas fungal levels were wide-ranging in the control homes (Figure 1).
Increases in airborne indoor fine particulates were observed in both the test (50.6% increase -
2.52 to 3.80 x 10-2 particles m-3) and control homes (210% increase - 1.36 to 4.22 x 10-2
particles m-3) following the first steam cleaning intervention. Airborne fine particulate levels
were reduced in the subsequent monitoring periods in the test homes whereas in the control
homes, fine particulate levels remained above the baseline pre intervention levels (Table 1).
Table 1. Mean airborne fine particulate levels in the test and control homes
Steam clean homes
x 10-2 particles m-3
Control homes
X 10-2 particles/m3
2.15 (1.59)
1.36 (1.33)
1.06 (0.91)
3.80 (3.03)
2.38 (2.60)
4.22 (1.74)
5.83 (3.69)
1.96 (2.50)
1.62 (1.28)
1.55 (1.24)
1.46 (1.34)
A small subset of samples was differentiated to provide a fungal profile of the homes.
Cladosporium, Penicillium and yeast were the most commonly isolated fungi in the indoor
and outdoor samples for the test homes (Table 2).
Table 2. Fungal genera distribution in the test homes
Time period
Steam clean homes (n=9)
Indoor species
Outdoor species
Pre intervention
21% Clad
29% Pen
5% Asp
7% Alt
1% Fus
7% Bot
1% Aur
8% Epic
15% Yeast
4% Sterile
28% Clad
33% Pen
3% Asp
11% Alt
2% Fus
6% Bot
1% Aur
3% Epic
6% Yeast
6% Sterile
Post intervention
27% Clad
31% Pen
3% Asp
5% Alt
1% Fus
1% Bot
1% Epic
27% Yeast
3% Sterile
34% Clad
23% Pen
3% Asp
8% Alt
1% Fus
2% Bot
3% Aur
12% Yeast
13% Sterile
* Clad = Cladosporium, Pen = Penicillium, Asp = Aspergillus, Alt = Alternaria, Fus = Fusarium, Epic = Epicoccum, Bot = Botrytis, Aur = Aureobasidium, Rhiz
= Rhizopus, Sterile mycelia refer to those fungal colonies that fail to grow reproductive structures and could not be identified.
Baseline indoor fungal levels
The baseline culturable indoor fungal levels reported in this study (mean = 344 CFU m-3)
were in the same range but slightly lower than those reported in studies of airborne indoor
fungi levels in residential Australian houses (median = 443 CFU m-3, 421 CFU m-3, 495 CFU
m-3, & 812 CFU m-3 (rural area)) (Godhish et al. 1996, Cheong et al. 2004, Dharmage et al.
2002, Garrett et al. 1997). This could be due to seasonal factors, with the sampling period for
this study conducted during the winter period.
Steam cleaning intervention
The initial increase in airborne fine particulate levels in both the test and control homes was
consistent with higher outdoor airborne fine particulates, recorded concurrently. Due to the
milder and warmer climate, homes in Western Australia, generally have a greater reliance on
natural ventilation rather than mechanical ventilation, with open windows and doors allowing
greater infiltration of outdoor air. The reliance on natural ventilation and the influence of
infiltration can also be seen in the fungal distribution in both the indoor and outdoor samples.
The fungal distribution and composition before and after the cleaning intervention were
unchanged and reflected a similar composition as that of the outdoor samples. Indoor fungal
levels in the test homes were significantly reduced following the intervention compared to the
control homes where indoor levels were wide ranging. This suggest that the cleaning
intervention was effective in not only maintaining a stable and lower indoor fungal levels, but
also a stable fungal composition, reflecting a similar composition with the outdoors (natural
infiltration and ventilation).
The wet extraction (‘steam cleaning’) method utilised in this cleaning intervention is
important in the overall cleaning maintenance regime for carpet care as it removes residual
chemicals and difficult to remove particulates deep within the carpet pile. As was discussed in
Cheong and Neumeister-Kemp (2005) and Bishop (2004), physical (occlusion in the fibre
surface structure and within the fibre bundle) and electrostatic forces combine to contribute to
strong adhesive forces trapping soil, dirt, fungi and particulates deep down within the carpet
pile. Regular conventional vacuum cleaning is not sufficient to break these forces. Intensive,
high efficiency vacuum cleaning using rotating brush heads could aid in breaking these
adhesive forces. However, stains and significant soilage deep in the carpet fibres requires wet
extraction to suspend and dissolve into solution the ground-in soil and dirt, for immediate
Once properly cleaned, the carpet could then act as a possible ‘sink’, retaining incoming
outdoor sources of fungal spores and particulates in the carpet fibres and prevents dirt from
being tracked around the rest of the home, resulting in an overall reduced dissemination of
spores and particulates into the indoor air (Cheong & Neumeister-Kemp 2005, Darlington
2000). This is confirmed with the overall lower and stable levels of fungi recovered indoors in
the test homes compared to the wide-ranging levels in the control homes.
This study reconfirms results of similar studies by Berry (2002) and Bishop (1991),
demonstrating that wet extraction’ and regular vacuuming of carpet surfaces is highly
effective in reducing and managing levels of airborne fine particulates and indoor culturable
fungal spores.
Special care must be taken to ensure that the carpet is dry and moisture free after the wet
extraction cleaning. Wet extraction cleaning must only be conducted by experienced and
accredited carpet cleaners. Additional air movers or dryers can be utilised to quicken the
drying process. Inexperienced and unaccredited carpet cleaners or poor cleaning techniques or
equipment could lead to excessive wetting of the carpet causing excess moisture to be left in
the carpet pile, resulting in ideal conditions for mould growth and proliferation.
Conducting a ‘wet extraction’ cleaning intervention alone does not guarantee low indoor
airborne fine particulate and fungi levels if there is poor ongoing vacuuming and maintenance
over the long term. The continual reduction of potential resuspended pollutants by the removal
of these pollutants on the surface of the carpet by regular vacuuming is a major element in the
continual maintenance of carpets over a longer time period. Poor maintenance will lead to an
increase and build up of bio contaminant loadings such that the carpet no longer serves as a
sink but itself becomes a source of contamination (Cheong & Neumeister-Kemp 2005, Foarde
& Berry 2004).
An examination and analysis of changes in fungal profile and particulate characteristics of
dust samples present in the carpet pile, and its relationship with the airborne component, could
provide more detailed knowledge in the area of cleaning interventions.
The authors would like to thank Kevin White, Jane Jones, Scott Smith, Rita Tan and Joanne
Nastov for their assistance in the field.
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Publication: Proceedings of Indoor Air 2005, The 10th International Conference on Indoor
Air Quality and Climate
Please complete the information requested as follows:
Corresponding author: Cedric D. Cheong
Affiliation: School of Environmental Science, Murdoch University
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Co-author(s): Dr H.G.Neumeister-Kemp and Dr P.W.Dingle
Paper ID: 769
File name uploaded to Paper 769 (Steam cleaning
Manuscript title: Effect of steam cleaning carpets on airborne viable fungi and fine
particulates in residential homes
Paper topic: 4.7 Cleaning and maintenance
Index words: Steam cleaning, carpets, indoor fungi, fine particulates, wet extraction,
residential homes, vacuuming
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Abstract Five floors of a 20-year old 6-story office building were investigated using an integrated step-by-step investigation strategy. This involved a walkthrough inspection, an occupant questionnaire, and targeted environmental monitoring of indoor air quality and comfort parameters. The initial questionnaire survey revealed a high occurrence of building-related symptoms. The walkthrough inspection and environmental monitoring identified deposits of surface dust (indoor surface pollution – ISP) on carpets and hard surfaces, and elevated levels of carbon dioxide and respirable suspended particulate matter (RSP) throughout the building. An intervention study (blinded to the occupants) was targeted at reducing ISP levels by replacing normal carpet cleaning practices with higher performance vacuum cleaners and improved cleaning practices. The intervention reduced ISP levels and significantly lowered RSP concentrations by approx. 80% from initial values and against control floors. A follow-up SBS questionnaire revealed significant reductions in all but two of the symptoms. The most significant reductions occurred with symptoms of eye irritation, throat irritation, dry unproductive cough, and nose irritation. The study showed that in older buildings with poor ventilation, a build-up of ISP, and elevated RSP levels, using higher performance carpet cleaning practices can reduce RSP to acceptable levels and can reduce SBS symptoms.
Abstract A study was conducted to characterize the indoor environment of a multifloor, multiuse, nonproblem, noncompliant building through long-term monitoring for biological, chemical, and particulate pollutants. The study also assessed the effects of cleaning on indoor air quality by providing a program to monitor baseline levels, providing a rigorous (deep) cleaning of the building, and then continuing to monitor after implementation of a standardized, improved, cleaning program. To assess the effectiveness of the cleaning program, air, surface, and dust data from monitoring prior to the cleaning program were compared with those obtained while the improved housekeeping program was in place. Correlations between pollutants and other environmental factors were studied. The data suggest that the improved cleaning program contributed to indoor air quality through the reduction of airborne dust mass, total volatile organic compounds, and culturable bacteria and fungi.
Airborne viable and total fungal spores were sampled inside and outside 80 houses in the Latrobe Valley, Victoria, Australia as part of a larger indoor environmental study. Each residence was visited six times over a period of 1 year for sample collection, and fungal spore samples were collected from at least three indoor sites and from an outdoor site. Viable spores were sampled using an Andersen sampler, while total spores were assessed using a Burkard spore trap. Identification of fungal colonies to genera level was performed in two seasons; winter and late spring. The most common fungal genera/groups wereCladosporium, Penicillium, and yeasts, both indoors and outdoors in winter and late spring. Outdoor levels were higher than those indoors throughout the year, and a significant seasonal variation in spore levels was seen both indoors and outdoors with overall maxima in summer. Contrary to this trend, the levels ofAspergillus, yeasts,Cephalosporium andGliocladium were higher in winter. Most fungal genera were found in greater concentrations outdoors compared to indoors, butPenicillium was more common indoors. Outdoor spore levels were a significant influence on indoor levels, but seasonal differences suggest that other influences are important.