Washing machines are a reservoir of multidrug-resistant pathogens


For the first time ever, investigators have identified a washing machine as a reservoir of multidrug-resistant pathogens.

The pathogens, a single clone of Klebsiella oxytoca, were transmitted repeatedly to newborns in a neonatal intensive care unit at a German children’s hospital.

The transmission was stopped only when the washing machine was removed from the hospital.

The research is published this week in Applied and Environmental Microbiology.

“This is a highly unusual case for a hospital, in that it involved a household type washing machine,” said first author Ricarda M. Schmithausen, Ph.D. Hospitals normally use special washing machines and laundry processes that wash at high temperatures and with disinfectants, according to the German hospital hygiene guidelines, or they use designated external laundries.

The research has implications for household use of washers, said Dr. Schmithausen, Senior Physician, Institute for Hygiene and Public Health, WHO Collaboration Center, University Hospital, University of Bonn, Germany.

Water temperatures used in home washers have been declining, to save energy, to well below 60°C (140°F), rendering them less lethal to pathogens. Resistance genes, as well as different microorganisms, can persist in domestic washing mac

hines at those reduced temperatures, according to the report.

“If elderly people requiring nursing care with open wounds or bladder catheters, or younger people with suppurating injuries or infections live in the household, laundry should be washed at higher temperatures, or with efficient disinfectants, to avoid transmission of dangerous pathogens,” said Martin Exner, MD, Chairman and Director of the Institute for Hygiene and Public Health, WHO Collaboration Center, University Hospital/University of Bonn.

“This is a growing challenge for hygienists, as the number of people receiving nursing care from family members is constantly increasing.”

At the hospital where the washing machine transmitted K. oxytoca, standard screening procedures revealed the presence of the pathogens on infants in the ICU.

The researchers ultimately traced the source of the pathogens to the washing machine, after they had failed to find contamination in the incubators or to find carriers among healthcare workers who came into contact with the infants.

The newborns were in the ICU due mostly to premature birth or unrelated infection.The clothes that transmitted K. oxytoca from the washer to the infants were knitted caps and socks to help keep them warm in incubators, as newborns can quickly become cold, even in incubators, said Dr. Exner.

The investigators assume that the pathogens “were disseminated to the clothing after the washing process, via residual water on the rubber mantle [of the washer] and/or via the final rinsing process, which ran unheated and detergent-free water through the detergent compartment,” implicating the design of the washers, as well as the low heat, according to the report.

The study implies that changes in washing machine design and processing are required to prevent the accumulation of residual water where microbial growth can occur and contaminate clothes.

However, it still remains unclear how, and via what source the pathogens got into the washing machine.

The infants in the intensive care units (ICU) were colonized, but not infected by K. oxytoca. Colonization means that pathogens are harmlessly present, either because they have not yet invaded tissues where they can cause disease, or because the immune system is effectively repelling them.

The type of multidrug resistance in the K. oxytoca is caused by extended spectrum beta-lactamases (ESBL). These enzymes disable antibiotics called beta lactams. The most common types of bacteria producing ESBLs are Escherichia coli, and bacteria from the genus Klebsiella.

Journal information: Applied and Environmental Microbiology
Provided by American Society for Microbiology

Soft surfaces and laundry as infection reservoirs

Privacy curtains

Among the infection reservoirs more recently described are soft surfaces such as furniture, mattresses, pillows and privacy curtains. Trillis et al. [53] found 42% of curtains surrounding patients’ beds to provide privacy to be contaminated with VRE, 22% with MRSA and 4% with C. difficile (also see [54]).

Transmission of bacteria from curtains via the hands of healthcare personnel touching these curtains is possible ([55], [56] and chapter on laundry as infection reservoir below). In 2002, Das et al. reported an outbreak caused by a Carbapenem-resistant Acinetobacter baumannii in an intensive care unit of the tertiary-referral university teaching hospital in Birmingham with curtains surrounding patients’ beds as the major source [57].

A recent publication by Mahida et al. from Nottingham, U.K., describes an outbreak of invasive group A streptococcus infection (GAS) on an ear, nose and throat ward, where contaminated patient curtains were found to be the potential source of GAS cross-transmission, which had implications in relation to hand hygiene and frequency of laundering [58].

Possible decontamination practices include wiping the “grab area” of the curtain with improved hydrogen-peroxide containing disinfectants [59].

Increasing awareness of the problem is reflected in publications such as “Divider Curtains and Infection Risks” by the Canadian Comité sur les infections nosocomiales du Québec [60] at the end of 2013. A standard protocol for microbiologically safe use of hospital curtains has yet to be established.


Textiles as common-touch surfaces tend to get overlooked as infection reservoir because of the lack of intervention study data showing a direct link to infection. However, they also must be regarded as a potential vehicle of infection (before, during and after handling laundry), with the risk increasing where large quantities of pathogens are shed via vomit, faeces and skin, and where people have impaired immunity.

This includes residential facilities for the elderly, where a hygiene regimen covering the whole process from collecting laundry to adequate storage is required. Apart from controlling infection risks, effective laundering is also important to prevent the spread of antibiotic-resistant skin and intestinal flora such as MRSA and multidrug resistant Gram-negative strains in domestic and medical settings.

In 2011 IFH carried out a review of the data on infection risks associated with clothing, bedlinens etc. in community, hospitals and other healthcare settings [61]. The greater part of the data comes from studies showing how pathogens are shed onto, or transferred to, clothing etc., and the extent to which they can survive and spread to hands and surfaces such that we can become exposed to potentially infectious doses.

The data show that viability on fabrics declines at a more or less rapid rate on dry clothing, depending on the microbial species and room humidity. Generally, survival of microbes on fabrics is significantly less than on non-porous contact surfaces. However, Gram-positive spp. such as S. aureus, C. difficile and fungal spp. can survive long periods (days to months) on fabrics. Survival times for Gram-negative species such as E. coli and P. aeruginosa are shorter, but survival times of up to 4 h or more have been recorded.

Survival of viruses on fabrics is mostly around 30 min up to 12 h, up to a maximum of 48 h (no data are available for norovirus), whilst survival times for fungal species ranged from 1 day to several weeks.

Transfer rates from moist fabrics to hands and other fabrics were around 1–10%, but in some cases, transfer was as little as 0.1% or less, or as high as 50% [55], [56]. Transfer rates varied according to microbial strain, temperature, room humidity, type of fabric and inoculum size. They are significantly lower (up to a 10-fold decrease), if donor fabrics or hands are dry. Another possible pathway is air-borne transmission, e.g. after shaking sheets or linen when changing bedding [62].

Although no intervention studies were identified, the IFH review includes around 19 epidemiological studies for which transmission via clothing and linens was identified as a likely cause or a significant risk factor. These included gastrointestinal and respiratory tract, together with skin and wound infections associated with clothing, shared towels (e.g., CA-MRSA), bed linen (Acinetobacter), feather pillows, and babies’ vests [63], [64], [65].

Monitoring effectiveness of laundering is another key issue. During the laundering process, temperature, duration of the wash cycle, mechanical action of water, and detergent all work together to reduce contamination levels on fabrics. In addition to physical removal, microorganisms can be killed not only by heat but also by chemical action. Other contributing factors are drying and ironing.

Maintenance and care of the washer in order to prevent biofilm formation is also essential. A 2013 review by IFH comprising 29 publications on the effectiveness of laundering showed that a decrease in laundering temperature can significantly increase numbers of survivors on contaminated fabrics [66]. In situations where there were significant survivors, microbes were transferred to other items included in the wash. By contrast, efficacy can be increased, if components which release active oxygen bleach are included in the detergent formulation [67], [68], [69], [70].

A 2011 study by Lakdawalla [71] showed that up to 101–103 cfu/100 cm2 of Clostridium difficile could be detected on naturally contaminated bed linen even after a commercial washing process at 71°C, 3 minutes, with subsequent steam ironing in accordance with the HSG(95)18 requirements for hospital laundry arrangements for used and infected linen, U.K. Department of Health. Whether these low numbers of spores represent an infection risk is disputable, but the results suggest that there is a potential for cross-contamination of laundry during the laundry process.

A serious concern is the fact that low temperature or cold water laundering is increasingly being used in domestic settings in order to conserve energy and because many fabrics are not compatible with higher temperature laundering. Other studies are also showing that domestic washing machines often fail to reach the prescribed temperatures [72]. In private households, visibly clean laundry is perceived as being hygienically safe and falsely considered as evidence of an effective washing process.

A major difficulty of interpreting the data in the IFH 2013 report is the extent of the variability in the results obtained from different studies under any given set of conditions. This is reflected by the diversity of recommendations for hygienic laundering of clothing in healthcare and domestic situations given by different agencies. There is an urgent need to study the impact of the key variables under carefully controlled conditions.

A recent study shows the importance of environmental monitoring of potential infection reservoirs, and how delay in identifying a potential source of infection may increase the risk of infection. In 2013, Exner et al. (personal communication) evaluated reports of increased carriage of K. oxyctoca in the pediatric unit of a German hospital. An investigation revealed the existence of K. oxytoca in ward sinks, but hygiene interventions did not terminate the “outbreak”. It was not until further investigation when the presence of K. oxytoca was detected in the door seals of the washing machine, which was situated in another part of the hospital, that the probable source was identified. Retrospective study showed that only infants whose clothes were laundered in this specific machine became colonised. Following this finding, transmission could be completely stopped and the outbreak was brought under control.


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