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Laundry Hygiene and Odor Control: State of the Science
Sarah E. Abney,
a
M. Khalid Ijaz,
b,c
Julie McKinney,
b
Charles P. Gerba
a
a
Department of Environmental Science, University of Arizona, Tucson, Arizona, USA
b
Global Research & Development for Lysol and Dettol, Reckitt Benckiser LLC, Montvale, New Jersey, USA
c
Department of Biology, Medgar Evers College of the City University of New York (CUNY), Brooklyn, New York, USA
ABSTRACT Laundering of textiles—clothing, linens, and cleaning cloths—functionally
removes dirt and bodily fluids, which prevents the transmission of and reexposure to
pathogens as well as providing odor control. Thus, proper laundering is key to controlling
microbes that cause illness and produce odors. The practice of laundering varies from
region to region and is influenced by culture and resources. This review aims to define
laundering as a series of steps that influence the exposure of the person processing the
laundry to pathogens, with respect to the removal and control of pathogens and odor-
causing bacteria, while taking into consideration the types of textiles. Defining laundering
in this manner will help better educate the consumer and highlight areas where more
research is needed and how to maximize products and resources. The control of microor-
ganisms during laundering involves mechanical (agitation and soaking), chemical (deter-
gent and bleach), and physical (detergent and temperature) processes. Temperature plays
the most important role in terms of pathogen control, requiring temperatures exceeding
40°C to 60°C for proper inactivation, while detergents play a role in reducing the microbial
load of laundering through the release of microbes attached to fabrics and the inactiva-
tion of microbes sensitive to detergents (e.g., enveloped viruses). The use of additives
(enzymes) and bleach (chlorine and activated oxygen) becomes essential in washes with
temperatures below 20°C, especially for certain enteric viruses and bacteria. A structured
approach is needed that identifies all the steps in the laundering process and attempts to
identify each step relative to its importance to infection risk and odor production.
KEYWORDS laundry, hygiene, odor, pathogens, laundering
As highlighted in recent reviews, laundering plays an important role in the control
of both pathogenic and odor-causing microorganisms (1, 2). Microflora will vary
from one household, community, and region to another. Traditional laundering
practices, socioeconomic factors, the availability of washing facilities, and the selection
of products will influence many of these factors. Today, most laundry washing is
conducted with machines (;80%) (3), even in less-developed countries. However,
handwashing is still practiced in developed countries, especially with delicate or non-
machine-washable fabrics.
Most studies on laundering have focused their evaluation on practices within high-
income countries, mostly involving machine washing. However, handwashing occurs in
both high- and low-income countries to various degrees (3). Laundering procedures vary
from region to region and are influenced by cultural practices and resources. Laundering
involves a series of steps, independent of income status or machine access, each of which
can affect the removal and diversity of dermally shed transient microflora within the textiles
being processed. The goal of this review is to define laundering as a series of steps that influ-
ence the exposure of the person processing the laundry to pathogens and the removal and
control of pathogens and odor-causing bacteria while taking into consideration the types of
textiles. Defining laundering in this manner will help better educate the consumer and high-
light areas where more research is needed and how to maximize products and resources.
Citation Abney SE, Ijaz MK, McKinney J, Gerba CP.
2021. Laundry hygiene and odor control: state of
the science. Appl Environ Microbiol 87:e03002-20.
https://doi.org/10.1128/AEM.03002-20.
Editor Christopher A. Elkins, Centers for
Disease Control and Prevention
Copyright © 2021 Abney et al. This is an open-
access article distributed under the terms of
the Creative Commons Attribution 4.0
International license.
Address correspondence to Sarah E. Abney,
seabney@email.arizona.edu.
Accepted manuscript posted online
7 May 2021
Published 25 June 2021
July 2021 Volume 87 Issue 14 e03002-20 Applied and Environmental Microbiology aem.asm.org 1
MINIREVIEW
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MICROFLORA OF CLOTHING
The microflora of laundry is important from the aspects of both preventing the transmis-
sion of diseases and odor control. The microflora of household laundry can be influenced
by many factors, including textile attributions, handling, and usage (Table 1).
MICROBES IN LAUNDRY
The source of most microbes in clothing is the human skin and bodily excretions and
secretions. Activities such as cooking and eating, outdoor activities, and occupation can
influence the distribution of the microbial flora present on the skin and within bodily
excretions. Linens (bedsheets), cleaning tools (sponges, kitchen towels, and dishcloths),
TABLE 1 Factors influencing the occurrence of bacteria/viruses/molds in laundry
Factor(s) Description Reference(s)
Fabric composition Thickness, material, coloring agents; the thicker
the fabric, the greater the survival of bacteria
during laundering; greater survival of coliforms in
hand/face towels after laundering and drying
S. K. Tamimi, S. L. Maxwell, L. Sifuentes, and C. P.
Gerba, unpublished data; Gerba, unpublished
Storage conditions Bacterial no. increases in hampers and if stored
under high humidity (molds and total bacterial
no.); we have found that clothing stored in
hampers between laundering can result in the
growth of bacteria in clothing
Kennedy and Gerba, unpublished
Usage Location on body where worn (higher no. on
undergarments and in pockets than on shirts; face
and kitchen towels have higher no.); length of
time worn; highest no. of enteric bacteria found
in face towels and underwear
(e.g., coliforms)
10; Gerba et al., unpublished
Season Higher no. of bacteria during summer (mold);
warmer weather and perspiration encourage
growth of bacteria
K. A. Reynolds and C. P. Gerba, unpublished data
Age of clothing Possibility of biofilm buildup; microorganisms
adapt to repeated washing conditions and are
not always removed
Reynolds Gerba, unpublished
Type of detergent Additives to enhance detergent performance, i.e.,
enzymes and multiple surfactants
Reynolds and Gerba, unpublished
Dirt load Type and quantity affect the performance of
detergent and bleach
Kennedy and Gerba, unpublished
Wash temp and time Greater survival of microbes at lower temp 45, 62; Kennedy and Gerba, unpublished
Drying temp and time Greater survival at lower temp and shorter length
of drying time
45; Kennedy and Gerba, unpublished
Air drying Bacterial no. may increase in the clothing under
humid outdoor conditions; prolonged exposure
to sunlight may decrease no. of fungi
13
Type of microorganism Resistance of microorganisms to washing varies
with species and strain of microorganism;
Mycobacterium,Enterobacter, and enteric viruses
are more resistant to release from textiles and
removal
13, 45; Kennedy and Gerba, unpublished
Concn of microorganisms in bodily
excretions or secretions
Enteric viruses and bacteria can be excreted in
high concn in feces; Salmonella occurrence at
concn as high as 10
10
bacteria/g and norovirus
occurrence at concn as high as 10
11
particles/g of
feces
63
Concn of bodily excretions or
secretions in clothing
The avg pair of adult underwear contains an avg
of 0.1 g of feces
63
Method of washing Machine washing versus handwashing; no data
found on handwashing but expected to be less
efficient
3
Quality of wash water In developing countries, fecally contaminated
water may be used, such as in streams
39
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and bath towels can have their unique microflora. Each group of textiles has unique fea-
tures such as types of fabric, usage, and dirt load. This also influences the occurrence of
pathogens and odor-producing bacteria within laundry.
Pathogens. Epidemiological studies have suggested the role of fabrics in transmit-
ting infectious agents in facilities (4). Since most pathogens associated with textiles
have multiple transmission routes, tracing epidemiological associations with launder-
ing and transmission is difficult. One study suggested the spread of respiratory illness
associated with public laundromat usage and not using bleach during laundering (5).
Numerous pathogens have been detected in textiles before laundering (Table 2).
Any pathogen associated with human illness is likely to be found in clothing and most
other textiles. Outbreaks of illness have been associated with textiles contaminated
with pathogens (viruses, bacteria, and fungi, where most cases are associated with
health care workers and facilities [1, 6, 7]).
Bacteria. Pathogenic bacteria causing enteric disease (Salmonella) and skin infec-
tions (MRSA [methicillin resistant Staphylococcus aureus]) have been associated with
textiles. In one study, Salmonella was detected in 15% of household sponges in the
United States and 3% of hand/face towels (8). Escherichia coli and other enteric bacteria
were also common. E. coli has also been detected in reusable grocery bags (9). Fecal
bacteria are common in undergarments of both children and adults (10). Under condi-
tions of storage (hamper or closet) before or after laundering, bacterial numbers can
increase (11).
Fungi. It has been suggested that fungi present in clothing may also play a role in
the transmission of dermatitis and onychomycosis (infection of the nails) (12). Fungal
pathogens have been isolated from patients suffering from tinea pedis (13). Clothing
has been linked to the transmission of Microsporum canis (1). M. canis belongs to the
TABLE 2 Some pathogens detected in textiles before washing
Organisms
a
Reference(s)
Bacteria
Salmonella enterica serovar Typhimurium 1
S. enterica serovar Hadar 1
Acinetobacter baumannii 1
MRSA 1
Bacillus cereus 64
Clostridium difficile 33,42
Neisseria gonorrhoeae 1
Vancomycin-resistant enterococci 42
Fungi
Microsporum canis 1
Sarcoptes scabiei 64
Alternaria alternata 65
Trichophyton mentagrophytes 13
Viruses
Hepatitis B virus 1
Hepatitis A virus 66
Papillomavirus 67
Rhinovirus 68
Adenovirus 69
Influenza virus 68
SARS-CoV-2 58
Parainfluenza virus 68
RSV 68
Rotavirus 70
Helminths and protozoa
Pinworms 18
a
RSV, respiratory syncytial virus.
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group of dermatophyte fungi, which are closely related microorganisms that can
invade the stratum corneum of the epidermis and keratinized tissues derived from it,
such as the skin, nails, and hair of humans and animals. These fungi produce an infec-
tion called dermatophytosis, commonly referred to as ringworm or tinea. Of 70 house-
hold washing machines sampled in one study, 79% were positive for fungi (14).
Among the species detected, the opportunistic fungi Candida and Fusarium were
detected. Fungi can also cause life-threatening infections among the immunocompro-
mised. Mucormycosis, an infection of the order Mucorales, can cause mortality rates
that can exceed 50% (15). Outbreaks have been associated with linens in health care
(16). It was found that 33% to 73% of recently laundered linens were contaminated
with Aspergillus (16).
Protozoa. While no studies on the occurrence of protozoa in fabrics could be
found, they can be expected to be present in fecally soiled clothing from infected indi-
viduals as well as individuals who work with animals, such as farmers, cattle operators,
and veterinarians. In an outbreak of cryptosporidiosis, a wife was infected through
washing her husband’s soiled veterinary clothing (17).
Viruses. A wide range of enteric and respiratory viruses have been detected in tex-
tiles, including rotavirus, hepatitis A and B viruses, herpes simplex virus, severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza virus, HIV, and papillomavi-
rus (Table 2). A blood-borne pathogen, hepatitis B virus has been transmitted by shar-
ing bathroom towels. Hepatitis A virus and vaccinia virus (smallpox virus) have also
been shown to be transmitted by textiles (1).
Helminths. Fecally contaminated clothing and fabrics can also be expected to contain
helminths (worms) and their eggs. These include tapeworms, Ascaris,andpinworms,etc.
Good hygiene and water and food supplies have resulted in a low incidence of most intesti-
nal worm infestations in the developed world. Pinworms are the most common helminth in
the United States and Western Europe, with prevalence rates in some communities being as
high as 30% to 50% (18). It has been suggested that pinworm (Enterobius vermicularis)con-
tamination of bed linen and clothing could be involved in their transmission (18). Pinworm
and Ascaris eggs can survive for 2 to 3 weeks on clothing and bed linens (19, 20). No data
on the occurrence of helminths in clothing and fabrics could be located.
SURVIVAL OF PATHOGENS IN LAUNDRY
The survival of microorganisms in stored-before-laundering fabrics depends on sev-
eral factors, including relative humidity (RH), temperature, and material. Proceeded by
a lower rate of inactivation, most microbial inactivation takes place during drying of
the original suspension that contains the microorganism (e.g., saliva or mucus). Drying
of respiratory viruses results in a usual 10- to 100-fold reduction in titers (21). Some
microorganisms survive better at certain relative humidities than others. For example,
rotavirus survives well at high (85% 65%) and low (25% 65%) relative humidities on
cotton-polyester (22). The type of material and the presence of dyes or coloring agents
may also affect the persistence of microorganisms on/in textiles (23, 24; C. P. Gerba,
unpublished data). Water loss was observed to be greater in more hydrophobic fabrics.
Certain fabrics such as cotton towels hold moisture to a higher degree, reducing drying
and allowing the potential growth of bacteria and mold (C. P. Gerba and L. Sifuentes,
unpublished data). Kampf (21) found that bacteria at room temperature survived the
longest on polyester (up to 206 days), compared to 90 days in cotton and mixed fibers.
Most bacteria were found to survive better at higher relative humidities. Enveloped
viruses survived for less than 1 day on cotton fabrics, while they survived for 7 to
12 days on polyester. The thickness of the clothing/fabric may also affect drying and
cause the regrowth of bacteria, such as coliforms in face towels (Gerba, unpublished).
Dyes used in the manufacturing of fabrics may also have antibacterial activity (23).
Most respiratory viruses, including SARS-CoV-2, do not survive more than a day or
two in clothing (25, 26). The survival of influenza virus in clothing was found to be
related to the rate of water loss during drying (24). The thickness of the cloth and its
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color were related to survival, with faster inactivation in black cloth. However, some en-
teric viruses, such as rotavirus and hepatitis A virus, may survive for weeks (25, 27).
Pathogenic bacteria and molds, such as Salmonella and MRSA, may survive for
weeks in clothing (1). Naturally occurring Pseudomonas aeruginosa and Acinetobacter
spp. can grow in clothing even after laundering the clothing of wastewater treatment
workers (28). Apparently, naturally occurring bacteria have adapted to laundering con-
ditions, and enough organic matter remains for their regrowth during storage after
laundering.
At a temperature of 25°C and an RH of 50%, 21 days were required for a 90% reduction
in Giardia cysts in soiled 100% cotton (29). Under the same conditions, Cryptosporidium
oocysts required ;60 days. Furthermore, Entamoeba histolytica cysts, pinworm (Enterobius
vermicularis), and Ascaris suum ova at temperatures of ,25°C and 50% RH required 21, 26,
and 188 days for 3-log
10
reductions in soiled 100% cotton (30).
REMOVAL OF PATHOGENS AND ODOR-CAUSING MICROBES BY LAUNDERING
The removal of microbes by the laundering process depends upon several factors,
as illustrated in Fig. 1. As can be seen, many factors may influence the removal (detach-
ment and/or inactivation) of microorganisms but also the potential for contamination
(e.g., occupation, such as a wastewater worker versus a schoolteacher). It is likely that
these factors also result in the establishment of a resident microflora adapted to com-
binations of these factors. This is important to note as processes intended to detach
and inactivate microorganisms may introduce additional microbial communities (e.g.,
resident microflora from washers and dryers) and may influence malodors.
The removal of pathogens from the laundry is largely dependent on washing and dry-
ing practices. The reduction-release and/or inactivation of pathogens is influenced by de-
tergent selection, other additives (bleach), water temperature, and drying. In North
America, cold-water washes, using water from a cold-water tap, are commonly practiced.
Enveloped viruses such as SARS-CoV-2 and influenza virus are very sensitive to the re-
moval/inactivation capability of some detergents, which can result in the elimination of
these viruses even in cold-water washes (31, 32). The median cold-water wash tempera-
ture is 14.4°C (57.9°F) in the United States. It has been recommended that temperatures of
40°C to 60°C (104°F to 140°F) and/or the use of bleach is needed for more resistant enteric
and dermal pathogens (1, 33). Drying also provides an additional barrier to transmission/
survival, with both the temperature and duration playing a role in disinfection (C. P. Gerba
and D. Kennedy, unpublished data). Higher-temperature settings and longer drying can
significantly reduce microbial numbers. Acinetobacter baumannii and Staphylococcus
FIG 1 Factors influencing the removal of microorganisms by laundering.
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aureus are among the non-spore-forming bacteria that are the most resistant to drying
and heat found in the laundry. Washing at temperatures above 60°C is necessary to
achieve a 99.9% reduction (35). Mycobacterium, fungi, and enteric viruses (hepatitis A virus,
adenovirus, and rotavirus) also require higher washing and drying temperatures for signifi-
cant reductions (1, 36; Gerba and Kennedy, unpublished). The use of activated-oxygen
bleach (AOB) in cold-water washes (,40°C) will significantly reduce the levels of bacteria
and viruses but may not eliminate them (2, 35). Gerba and Kennedy (unpublished data)
found that AOB was more effective in reducing Mycobacterium and enteric viruses than
chlorine bleach in the presence of detergent, probably because both the high pH of deter-
gent and the presence of dirt loads adversely impacted chlorine bleach activity.
STEPS IN LAUNDERING
Machine laundering is a series of steps involving sorting of cloths, loading of the
washer, removal from the washer, drying, and storage. Handwashing of textiles may
involve washing in a basin, public facility, or surface water source (river or reservoir).
Each step in the process results in the exposure of the individual handling the clothing to
pathogens in the clothing and potentially to any present in the water. Exposure may occur
by both contamination of the hands and microbial aerosols (37). Today, machine laundering
is the most common method of practice, but hand laundering is practiced in all regions of
the world (3). In high-income countries, this is usually limited to fine fabrics or other items
for which machine washing is not recommended (e.g., reusable grocery bags made of plastic
fibers). In North America, 82% of the laundry is machine washed, while in Africa and the
Middle East, only 45% is machined washed (3). From 6% to 14% of household laundry is still
handwashed depending upon the region of the world.
HANDWASHING OF LAUNDRY
Delicate fabrics, such as lingerie and reusable grocery bags, can be significantly con-
taminated with bacterial and viral pathogens (9, 38; Gerba, unpublished). The use of
sinks or plastic basins, often used for handwashing of fabrics, can result in contamina-
tion of the hands and cross-contamination if multiple items are washed. In addition,
such items are not washed at temperatures as high as those in washing machines and
are hang dried, not reaching temperatures reached in machine dryers.
In low-income countries, laundry bar soap is often used for washing instead of
detergents, which may reduce the efficacy of the processes in terms of dirt removal
and microbes (Fig. 2). In addition, water with fecal contamination may be used. A study
in India suggested that handwashing of laundry in fecally contaminated rivers was a
potential risk factor for the transmission of hepatitis E virus (39).
LAUNDRY PROCESSING
Laundry processing involves several steps, as shown in Fig. 3. Each step not only
involves potential exposure to pathogens but also can affect the overall microbial load,
including odor-producing bacteria.
Storage of the laundry in a hamper or humid environment can result in the growth
of odor-producing bacteria, molds, and, potentially, pathogenic bacteria (11, 40). The
FIG 2 Steps in handwashing as practiced in some regions of the developing world.
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soil load may also enhance the potential for the growth of these microorganisms.
Bacteria and fungi may survive for weeks to months in textiles (11). Enteric bacteria
and viruses are also capable of prolonged survival (weeks), with some respiratory
viruses surviving for at least several days (1, 25).
Sorting of the textiles could result in both cross-contamination of the textiles, the
surfaces where it is conducted, as well as the hands of the person doing the sorting
and aerosolization of pathogen-associated particulates. The same is true for loading of
the washing machine, removal of the laundry from the washing machine, and place-
ment in the dryer or hanging of the clothes to air dry (Gerba, unpublished). The dry
heat from the dryer can result in a significant reduction of microbes. Drying in the out-
door environment may result in a reduction of microorganisms from the UV rays in
sunlight. Still, the presence of humid air conditions could result in the regrowth of
some microorganisms, including recontamination events from bird droppings. Sorting
prior to hanging of the clothes can result in additional exposure. Sorting of the clean
clothes in the same area as the one used for sorting of the unwashed clothes can result
in additional cross-contamination. Also, handling dirty clothes and then sorting
washed clothes can result in cross-contamination. This cross-contamination web has
been reported in commercial laundries (41, 42). Furthermore, storage of the clothing
can result in the growth of bacteria and molds under humid conditions (28).
Pathogens. The removal of pathogens from the laundry is largely dependent on
washing (release and/or inactivation) and drying (inactivation) practices. The reduction
of pathogens is influenced by detergent selection, other additives (bleach), water tem-
perature, and drying (43). In North America, cold-water washes are the common practice,
while in Europe, hot-water washes are much more common; hot-water taps in the
United States alone are recommended to be set at a maximum of 49°C (120°F) to 52°C
(125°F) to avoid scalding (44). In Europe, the temperature on the washing machine is
selected by the user, and hot-water washes of .40°C are the usual practice (1). It has
been recommended that a minimum wash temperature of .40°C is necessary to impact
the detachment and sterilization of pathogens from laundry where AOB detergents are
not used (1). Wash temperatures of 60°C are recommended for fungi (13). Microorganisms
with greater resistance to removal by washing and drying include spore-forming bacteria
(Clostridium difficile), Mycobacterium spp., Bacillus cereus,Acinetobacter spp., Aspergillus and
other fungi, hepatitis A virus, adenovirus, rotavirus, and enteroviruses (45; C. P. Gerba,
S. Maxwell, L. Y. Sifuentes, and A. H. Tamimi, submitted for publication). Table 3 illustrates
the removal of different types of microorganisms by machine washing.
Enveloped viruses such as SARS-CoV-2 and influenza virus are very sensitive to the inac-
tivation action of detergents, which can result in the elimination of these viruses even in
FIG 3 Steps involved in home laundering using a washing machine.
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cold-water washes. However, viruses and some bacteria and fungi may require hot-water
washes, bleach, and high settings on dryers (31, 45). Heinzel et al. (31) found that while
enveloped viruses were inactivated by .99.99% as a result of washing textiles at 20°C,
temperatures of 30°C to 40°C in addition to a sanitizing detergent (AOB) were necessary
for the inactivation of nonenveloped viruses. Both chlorine bleaches and activated-oxygen
sanitizers result in increased reductions of pathogens in textiles (1, 35). Activated-oxygen
bleaches are common in detergents used in Europe but not the United States (1). While
bleach effectively reduces the number of bacteria and viruses, AOB was found to be more
effectiveinsimulatedwashingloads(2,6,46).ThismaybebecauseofthehighpHcaused
by the laundry detergent resulting in a lower efficacy of the bleach.
Recently, Zinn and Bockmuhl (47) found that the addition of acetic acid (final concentra-
tion, 0.75%) to a wash load of soiled fabrics and detergent reduced Pseudomonas aeruginosa,
E. coli,andStaphylococcus hominis by more than 7 log
10
units, while S. aureus was reduced
by 5.8 log
10
units. Such approaches may be useful in reducing pathogens in resource-limited
regionsoftheworldaswellashigh-incomeregions.
Odor-producing microorganisms. Bacteria and fungi are the major causes of mal-
odors in clothing. Odor-producing bacteria and fungi may originate not only from use but
also during storage or from cross-contamination between articles, the washing machine,
and even machine or hang drying (40, 48, 49). During slow air drying, these microorgan-
isms may increase in numbers (48). Greater malodors are more often associated with poly-
esters because the odor-producing hydrophobic compounds attach more strongly to
these fabrics than to cotton and are more difficult to remove by detergents alone (48).
Washing machines develop a unique biofilm influenced by detergents and high
temperatures. Thermophilic bacteria are more common in washing machines and
clothing as a result (50, 51). Proteobacteria are the predominant phylum of bacteria in
washing machines (51). Pseudomonas putida was found to be the most resilient biofilm
former in washing machines (52). Washing machines are believed to be a significant
source of bacteria and fungi that cause malodors in laundry (49). Kubota et al. (40)
reported that the species Mycobacterium osloensis was primarily responsible for mal-
odor in laundry. They found that it had the potential to generate the odor compound
4M3H (4-methyl-3-hexenoic acid) as well as a high tolerance to desiccation and UV
light.
Overall, it appears that the major causes of malodors are bacteria and fungi that
can survive laundering. Upon wetting, these bacteria can grow both in the washing
machine itself and within textiles.
IMPACT OF WASHING MACHINES ON MICROFLORA OF TEXTILES
Type of textiles. The ability to release microbes from textiles by washing is influ-
enced by their structure, fabric type, and thickness. For example, bath and face towels
TABLE 3 Log
10
reductions by machine drying temperature and duration
Organism(s) Log
10
reduction Method, drying temp, and time Reference
Rotavirus 0.32 Permanent cycle, 55°C, 28 min, cotton sheets 45
Hepatitis A virus 0.29
Adenovirus 1.36
S. aureus 2.89–2.50 Huebsch gas dryer, medium temp, 16 min,
cotton-polyester sheets
71
S. aureus 3.23 Cotton-polyester, 10 min, 46°C, 20 min 72
Serratia marcescens .3.84
Bacillus stearothermophilus 0.73
S. aureus 1.82 Permanent press cycle, 55°C, 28 min, cotton Gerba and Kennedy, unpublished
E. coli .4.16
S. Typhimurium 4.83
Mycobacterium fortuitum 0.14
Naturally occurring bacteria 0.5–1.0 175.6°C–177.8°C, 2 min 73
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make it more difficult to remove bacteria because of their thickness. Coliform bacteria
within bath towels have been found to survive washing in hot water and extended
drying (Gerba, unpublished). This suggests that the occurrence of odor-causing bacte-
ria may be greater in some types of materials than others (i.e., sponges and bath and
kitchen cleaning towels) (53).
Type of washing machine. Front-loader machines have become more common
since they reduce water usage and are more efficient. However, residual water that
remains in the machine may affect odors and result in cross-contamination of laundry.
In a survey of washing machines in homes, ;20% were found to harbor E. coli in the
drum (Gerba, unpublished). Fungal pathogens such as Candida and Fusarium species
have been detected in residential washing machines (14).
Exposure. The greatest exposure to pathogens occurs from handling the soiled
laundry before it is placed in the washing machine and handling the washed laundry
when either putting it in the dryer or hanging it to dry. The contamination of the
hands during these events can lead to infection of the individual handling the laundry.
This is especially true for enteric pathogens since movement of the hands to the
mouth (lips) results in direct access to the intestinal tract. Contact with contaminated
skin can result in the transmission of skin infections, and respiratory infections can be
transmitted from contact to the nose, eyes, and mouth.
The next greatest exposure results from removing the laundry from a dryer or dur-
ing collection after it has been hung to dry. Finally, the reuse of the fabric results in a
potential additional exposure. Exposure events from handling laundry are shown in
Fig. 4. The microorganisms may be transferred from the hand to the face, other
fomites, and food. We consider that the greatest risk is likely from hand-to-mouth con-
tact from directly handling the laundry.
Only a certain percentage of the microorganisms on the fabric is transferred to the
hand from contact with each other (54). The number transferred to the hands may depend
uponthetypeoffabric,themoisturecontentofthefabric,andthegrippingstrengthof
the individual. Exposure will also depend upon how many contaminated fabrics are
handled and how many times the face or mouth is touched (55). Generally, less transfer of
virus occurs from fabrics than from hard nonporous surfaces. Lopez et al. (56) found that
0.03% of MS2 virus was transferred to the hands from dry cotton fabric at low relative hu-
midity (15 to 32%) and that 0.3% was transferred at high relative humidity (40 to 65%).
Indoor humidity in the United States ranges typically from 40% to 60%. In contrast, the
rate of transfer of MS2 from hard surfaces (stainless steel) to the finger was 21% to 79%
depending upon the relative humidity (56). Rusin et al. (54) found that only 0.005% of the
bacterial virus PRD1 was transferred from dry cotton cloth to the hands. Alternatively, the
rate of transfer was 0.0005% from a cotton-polyester fabric. From a moist wet cotton dish-
cloth,itwas0.03%.Nodataonthetransferofrotavirustohandsonfabricscouldbefound.
The rate of transfer of human rotavirus from a stainless steel surface to the finger was
found to be 16.6% (57). Rusin et al. (54) found that 33.9% of the coliphage PRD1 virus was
FIG 4 Exposure events for handing and washing laundry.
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transferred from the hand to the mouth. No data could be found on the transfer of envel-
oped viruses from fabrics to hands or from hands to face. Such information would help
better define risks from handling laundry from persons with respiratory infections, includ-
ing SARS-CoV-2-associated coronavirus disease 2019 (COVID-19). Recently, SARS-CoV-2
RNA was detected from a sheet, a duvet cover, and a pillow cover, further highlighting the
paramount importance of proper handling procedures during the replacement and/or
laundering of used clothing of SARS-CoV-2 patients (58).
CONCLUSIONS AND RESEARCH NEEDS
The goal of laundering is to control both the exposure to pathogenic microorganisms
and odor. Both are interrelated, and the control of one implies the control of the other.
One of the biggest problems in assessing the efficacy of these goals for domestic laun-
dering processes is the lack of a consistent, structured approach to all the factors
involved. A structured approach is needed that identifies all the steps in the process and
attempts to quantify both risks of infection and mitigation of odor. One factor that needs
to be assessed is the strategies in the home that can be used to minimize environmental
impacts (energy usage) while still minimize odor and exposure to illness-causing
microbes. The use of low temperatures during laundering may require additional strat-
egies such as the use of a sanitizer and/or extended machine drying, especially when
certain enteric viruses and bacteria may be present. There is also a need to consider the
laundering of work and professional clothing, demographics of the household, regional
differences in laundering practices, and types of textiles. All of these are needed to pro-
vide guidance to households to maximize the benefits of laundering.
Research should be focused on providing information that can be used to identify
risks and how they can be reduced in a more quantitative fashion. Using event trees to
define the impacts of each process in laundering and quantitative microbial risk assess-
ment (10, 59) can quantify the impact of each process in terms of odor reduction and
risk of infection. These can then be used to develop guidance for domestic laundering,
which is not yet available and would have the greatest benefit. In fact, there are no
understandings of a definition for what it means to achieve a “safe”level of risk reduc-
tion in laundering practices. Research on the efficacy of machine washing alone has
only recently been detailed (60, 61). Figure 5 illustrates these needs. More information
on the types and concentrations of odor-causing and pathogenic bacteria in the laun-
dry can be used to better define strategies for processing while also taking into consid-
eration the demographics of the household with respect to the types and coarseness
of textiles (professional clothing, thickness, and use). In this regard, the best combina-
tion of products can be selected. Better information on the impact of storage before
and after laundering of textiles is also needed. We are now in an age of increasing con-
cern about the spread of emerging pathogens and means of prevention and control,
FIG 5 Research studies to better define and communicate risks associated with laundering.
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particularly with the ongoing SARS-CoV-2-associated COVID-19 pandemic. With addi-
tional information through future research endeavors, we can provide the best laun-
dering options to ensure a healthy household.
ACKNOWLEDGMENTS
M.K.I. and J.M. are employed through Global Research & Development for Lysol and
Dettol, Reckitt Benckiser LLC, Montvale, NJ, which is the funding source for this research.
Sarah E. Abney is funded by the National Science Foundation NRT Indigenous Food,
Energy, and Water Sovereignty research training grant #DGE1735173.
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