Decontamination of carpet exposed to Microsporum canis hairs and spores

Abstract

Objectives

The objective of this study was to evaluate the efficacy of vacuuming and three carpet cleaning methods for the removal of Microsporum canis spores and hairs from experimentally contaminated carpets.

Methods

Sterile Berber carpeting was artificially contaminated with naturally infective M canis hairs and spores. Carpet swatches were vacuumed for 10 s, 30 s and 60 s, and then cultured. Three carpet cleaning methods were evaluated on area rugs experimentally contaminated with infective material: a beater brush carpet shampooing, beater brush carpet shampooing post-disinfectant application and hot water extraction. Home cleaning products labeled as having efficacy against Trichophyton species were used in addition to 1% potassium peroxymonosulfate. Carpets were cultured at 24 h, 48 h and 7 days after cleaning. Good efficacy was no detectable spores at post-cleaning culture.

Results

All pretreatment carpet samples were culture positive for M canis (>300 colony-forming units [cfu]/site). Vacuuming did not decontaminate carpets but did remove intact hairs. Spores were not detected by wipe samples after two washings with an upright beater brush carpet shampooer or pretreatment with a disinfectant prior to carpet shampooing. Carpets cleaned with one hot water extraction technique had a decrease from 300 cfu/site to a mean of 5.5 cfu/site at 24 and 48 h post-cleaning and 2 cfu/site at day 7. The use of disinfectants was associated with odor, even when dry, and permanent discoloration. Hot water extraction cleaning was associated with the fastest drying time and no discoloration.

Conclusions and relevance

Carpets exposed to M canis can be disinfected via carpet shampooing or hot water extraction cleaning. Vacuuming of carpets is recommended to remove infective hairs. For homes, exposed carpeting can be decontaminated by routine washing with a carpet shampooer (twice) or hot water extraction. Use of pretreatment with a disinfectant is recommended when a high level of overall decontamination is needed in an animal facility with necessary carpeted surfaces (eg, entryway carpet mats).

Introduction

Environmental cleaning is a necessary part of the treatment of dermatophytosis. Spores protected within hair shafts can remain viable for long periods of time under certain conditions. From a clinical perspective the most important ramification is the risk of fomite carriage on the hair coat and false-positive fungal cultures and subsequent problems with diagnosis and/or monitoring of treatment. Successful decontamination of hard surfaces involves physical removal of soil prior to the use of disinfectants. ¹ Soft surfaces, for example laundry, can be disinfected via mechanical cleaning alone. ² Carpeting is a common soft surface that is readily soiled by pet hair. Carpet-cleaning studies have focused on reducing allergen load or bacterial bioload, but not the propagules of dermatophytosis. ³ Vacuuming has been recommended as part of disinfectant protocols; however, the efficacy of this alone has not been evaluated.^1,4 ‘Steam cleaning’ alone and the use of potassium peroxymonosulfate have been recommended for general decontamination of carpets, but, again, there are no studies evaluating their use against dermatophyte spores in carpeting. ⁵ The goals of this study were (1) to determine if vacuuming alone is adequate for decontamination and (2) to test the efficacy of three methods of decontamination of carpeting: mechanical washing alone (ie, ‘carpet shampooing’), mechanical washing after pretreatment with a surface disinfectant and hot water extraction cleaning.

Materials and methods

This study had institutional approval granted by the University of Wisconsin–Madison, School of Veterinary Medicine.

Pilot studies

Experiment 1: effect of vacuuming

An upright high-efficiency particulate air filter vacuum was used to vacuum artificially contaminated carpet swatches (100 cm²) for 10 s, 30 s or 60 s (n = 10 each). In order to prevent cross-contamination, the beater bar was disinfected pre- and post-cleaning with accelerated hydrogen peroxide (AHP) (Accel TB Ready to Use Liquid; Virox Technologies) and wipes (Accel TB Wipes; Virox Technologies); data were discarded if beater brushes were culture positive. Each time trial was repeated 10 times. Carpets were experimentally contaminated as described below.

Experiment 2: efficacy of carpet shampooing

Three newly purchased area carpets (2.5 m × 1.5 m) were used in this experiment (two exposed and one unexposed). The carpets were washed as recommended by the manufacturer of the carpet cleaning unit. Specifically, the carpet was vacuumed until no visible debris (ie, cat hair) was seen, scrubbed with a beater bar upright carpet shampooer and detergent with attached suction for 10 mins. The solution reservoir was cleaned, disinfected and refilled with clean water and the procedure repeated to rinse and remove detergent residue. The surface was repeatedly vacuumed using just the suction component of the machine until a paper towel pressed against the surface showed no moisture wicking (10 mins). Carpets were cultured at 24 h, 48 h and 7 days post-washing. These carpets were washed a second time to determine if two washings would adequately decontaminate carpets similar to repeat washing of exposed laundry.

Experiment 3: efficacy of carpet shampooing coupled with disinfectant pretreatment step

In this experiment, 10 new carpets were used and only treated once. After vacuuming, carpets were wetted for 10 mins with a disinfectant before carpet shampooing. Test products included 10 products with known antifungal efficacy: enilconazole solution (Clinafarm EC; Merck Animal Health); AHP (Accel TB Ready to Use Liquid); an AHP product with label claim for use as a ‘carpet disinfectant’ (H2Orange2 Concentrate 117; EnvirOx); ethoxylated alcohol mixture 3% (Simple Green; Sunshine Makers); 1% potassium peroxymonosulfate 21.41% and sodium chloride 1.5% (Trifectant; Vetoquinol); lactic acid 3.2% (Lysol; Reckitt Benckiser); quaternary ammonium 0.22% (Fantastik; SC Johnson & Son). Test products also included three commercial veterinary shampoos containing antifungal ingredients: miconazole 2%/chlorhexidine gluconate 2% (Malaseb Shampoo; DVM TEVA Animal Health); climbazole/chlorhexidine digluconate (Douxo Shampoo Chlorhexidine PS with Climbazole; Sogeval Laboratories); and ketoconazole 1%/chlorhexidine gluconate 2.3% (Ketochlor Shampoo; Virbac Animal Health). ⁶ The veterinary shampoos were tested as an alternative for clients who are not willing to use chemical disinfectants. The carpet cleaning unit was disinfected with AHP and cultured just prior to use.

Experiment 4: efficacy of commercial hot water extraction cleaning

In this experiment, three new carpets were experimentally contaminated and then cleaned once using a commercial hot water extraction cleaning process (Stanley Steemer). Carpets were vacuumed with a 600 psi vacuum and then subjected to a high-pressure hot water extraction cleaning method using a proprietary cleaning solution for 10 mins.

Sources of infective material

Naturally infective material was obtained from lesional, Wood’s lamp-positive untreated cats or kittens with naturally occurring Microsporum canis infections. M canis infection was confirmed via fungal culture and microscopic examination.

Laboratory procedures

Fungal cultures were grown on BBL Mycosel agar (Becton Dickinson) modified with phenol red as a color indicator. Plates were incubated at 28–30°C for 21 days and examined daily for growth and number of colony-forming units (cfu). The final cfu/plate was obtained on day 21; however, the cfu/plate did not change between day 14 and day 21. Confirmation of M canis was made via microscopic examination.

Sporicidal effects of carpet detergent

Sample solutions of the commercial rug shampoo and the proprietary cleaning solution used in the hot water extraction cleaning had no inherent sporicidal efficacy when tested using the isolated infective spore model. ⁷

Carpet

Test carpet was newly purchased and consisted of a nylon weave. The carpet was a low pile, small loop type, commonly referred to as ‘Berber’.

Experimental carpet contamination protocols

The same protocol was used for contamination of carpets in experiments 2, 3 and 4. Test sites (16 cm² each) were marked on each carpet using an indelible ink pen (20 test and 10 control sites). Intact hairs were placed in the center sites (n = 2) to mimic shedding of whole infected hairs. The other eight sites were exposed by brushing each site 20 times with M canis contaminated toothbrushes.

Detection of contamination

Different culture techniques were evaluated for detection of contamination on the surface of carpeting. Toothbrushes, cotton tip swabs, disposable dust cloths (Swiffer cloths; Proctor and Gamble) and Replicate Organism Detection and Counting plates (BD Sciences) designed for environmental studies of microbial contamination were evaluated. Pilot studies determined that there was no difference in detection of heavy contamination from the surface of experimentally contaminated carpets (see above). When carpet swatches were combed over kittens under treatment that were clinically recovered and had fewer than 10 cfu/plate, only contact plates and Swiffer clothes (20 wipes) were able to detect this low level of contamination. Swiffer clothes (20 swipes per area) were used for testing post-treatment because these were practical, accessible to clients and economical.

Confirmation of pretreatment contamination was made by wiping the tip of a cotton swab over the surface of experimentally contaminated site. For post-treatment testing, fungal culture plates were inoculated by pressing the Swiffer cloth to the surface of a fungal culture plate five times.

Data analysis

Descriptive data were collected for this study. For the purposes of this study, good disinfectant efficacy with respect to carpet cleaning practices was defined as a decrease in the number of pretreatment cfu from >300 to a non-detectable number of spores.

Results

All exposure sites were culture positive for M canis prior to disinfectant testing. The carpet shampooer was easily decontaminated after cleaning with AHP, and no data were discarded (Figure 1; Table 1).

Figure 1

Pre- and post-cleaning colony-forming units (cfu)/site at 24 h, 48 h and 7 days post-cleaning

Table 1

Mean number of colony-forming units/site at each culture point

	Culture point
Cleaning method	0	24 h	48 h	Day 7
Mechanical washing (once)*	>100	>300	>300	6.05
Washing after disinfectant application	>100	0.6	0.6	0
Hot water extraction	>100	5.9	5.9	2.1

*

No detectable spores after second washing

Experiment 1: efficacy of vacuuming

All of the carpet specimens showed heavy contamination before and after vacuuming at 10 s, 30 s and 60 s. Beater bristles were consistently disinfected after use; no data were discarded. Examination of the dirt bin revealed that vacuuming removed intact culture-positive hairs. Pre- and post-cultures were similar at all test times with too numerous to count cfu/plate.

Experiment 2: mechanical washing of carpets

After the first carpet shampooing, carpet site cultures were still culture positive at 24 h and 48 h. The culture plates showed a marked increase in the density of the growth at these two culture times. The increased growth density was likely due to spores being lifted to the surface of the carpet during cleaning and a positive effect of moisture on the carpet at the time of sampling. At day 7, there was a marked decrease in the number of cfu/plate to a mean of 6.7. Five sites had 10–20 cfu/site (median 14). All of these sites were at or within close proximity to sites where whole infective hairs were placed. Mechanical spread of spores was detected at the five randomly selected sites (1–5 cfu/site). Cultures obtained after the second washing showed no increase in the number of cfu/site at 24 h and 48 h (1–5 cfu/plate), and at day 7 carpet cleaning showed no detectable spores. Two washings of carpets had good efficacy.

Experiment 3: disinfectant pretreatment followed by washing of carpets

Pretreatment with a disinfectant revealed only four sites with growth (1–8 cfu/plate) at 24 h and 48 h. In addition, there was no increase in cfu/site post-washing, as observed in experiment 2. The sites where intact hairs had been placed had <8 cfu/site. No evidence of transfer was found and there were no detectable spores found at day 7 post-cleaning. Given the large spore challenge and that only four sites were culture positive with low numbers of cfu/plate, pretreatment of carpets with a disinfectant followed by shampooing was compatible with good efficacy. Application of disinfectants resulted in discoloration of the carpets. The veterinary shampoos lathered excessively and required repeat water rinsing before the carpet stopped lathering.

Experiment 4: commercial hot water extraction cleaning

Post-cleaning using a hot water extraction technique showed no increase in cfu/site at 24 and 48 h. The two sites where whole infected hairs were placed had 21 and 40 cfu/plate. Transfer of spores to other sites was found at all randomly selected five test sites with 1–2 cfu/site.

Discussion

There are a number of weaknesses in this artificial contamination study model but the most notable are the following. First, it is difficult to standardize the contamination exposure for the carpets and sites. Although the number of contamination brushings on any one exposure site was the same, the amount of infective material on the toothbrushes used varied. Efforts were made to use toothbrushes that were similar with respect to the amount of hair and Wood’s lamp-positive hairs (few or many), but this is only a crude approximation. Second, different carpet types and lengths were not tested so the results might not apply to carpets with longer fibers or different weaves, which may be easier or more difficult to disinfect. Third, testing was carried out on relatively small carpets and with great attention to detail. Results may differ in a home situation.

In spite of the above weaknesses, it was possible to decrease the bioload of infective spores in experimentally exposed carpets using all three cleaning methods: carpet washing with a detergent, carpet washing coupled with a disinfectant treatment, or hot water extraction. Each cleaning method had advantages and disadvantages. Carpet washing alone had good efficacy but two cleanings were needed to achieve this, making it labor intensive. One concern was an increase in the number of cfu/site immediately post-washing after the first washing at 24 h and 48 h. This increase was most likely due to a combination of spores being lifted to the surface of the carpet via the beater brushes and wetting of the carpets. It is unknown if this increase represents a risk; however, it seems prudent to minimize contact with wet carpeting. Pretreatment of carpets with a disinfectant before washing had good efficacy. There was no post-treatment increase in the number of cfu in the first 48 h post-cleaning or detectable evidence of transfer from contaminated to uncontaminated sites. This method was less labor intensive, but requires a user willing to apply disinfectants to a large surface area and disinfectants may discolor the carpets. Hot water extraction was the least labor intensive and may or may not be more costly than using a carpet shampooer depending upon rental costs. There was no post-treatment increase in cfu and carpets dried very quickly. Given the low number of cfu/site post-treatment it is reasonable to consider this method as also having reasonable efficacy.

It was not unexpected that vacuuming carpets did not decrease the bioload of dermatophyte spores. It is a practical recommendation because shed infective hairs are fragile and spores readily spill into the pile of the carpet. Rapid removal will help minimize contamination of the carpet making it easier to decontaminate. The recommendation to vacuum carpets to decrease gross contamination is supported by the findings of this study. ⁴ Removal of debris prior to carpet shampooing is a consistent step in ‘do it yourself’ machines or commercial cleaning.

The efficacy of the environmental disinfectants or the veterinary shampoos was not unexpected. The environmental disinfectants have been shown to be effective textile disinfectants against both M canis and Trichophyton species. ⁶ The miconazole, climbazole and ketoconazole shampoos have also been shown to have sporicidal efficacy in in vitro studies against M canis. ⁸ Although this pretreatment step was associated with good efficacy, it is not without problems that pet owners would find unacceptable. The disinfectants, including one formulated for use on carpets (H2Orange2), resulted in discoloration of the carpet and, in addition, the shampoos were hard to rinse from the carpets. The seven carpet disinfectants were odorous during use and the odor detectible even when carpets were dry. Given that non-chemical methods were shown to have good efficacy, treating carpets with a disinfectant is best reserved for specific situations. Specifically, situations where a high level of decontamination is needed to prevent disease transmission and the target carpet surface is necessary (eg, entry way floor mats at veterinary clinics) or in situations where cats, for example in a cattery under treatment, are persistently culture positive but lesion-free and Wood’s lamp-negative. With regard to the latter situation, review of the client’s overall cleaning practices should precede such a recommendation.

No other studies on decontamination of dermatophyte exposed carpets could be found in English-language searches. One study in the human literature comparing carpet cleaning with or without an attached germicidal lamp (253.7 nm ultraviolet C) showed that the unit with the lamp doubled the effectiveness in reducing surface bound microbial load; however, there is no mention of dermatophyte spores. ³ Another study in the human literature evaluated the efficacy of direct application of disinfectants to carpets artificially exposed to feline calicivirus as a model for disinfecting surfaces contaminated with noroviruses. ⁹ An interesting finding was that different carpet types (olefin, polyester, nylon, blended carpet) were easier to disinfect than other types; however, a 10 min contact time resulted in 99% inactivation of the virus on all types. ⁹ The present study did not evaluate different carpet types, but a 10 min contact time for disinfectants (experiment 3) was used. A recent study evaluating the inactivation of mold spores (non-dermatophyte) from moist carpets using steam vapor found that 12 s of contact was needed to remove 90% of mold from moist carpets. ¹⁰ In the present study, hot water extraction of M canis showed no increase in the number of cfu per test site at 24 h and 48 h, suggesting that large amounts of infective material and moisture were removed during the cleaning process. The findings in this study were consistent with other studies that show if an exposed soft surface can be washed it can be decontaminated.^2,11,12

Conclusions

This study found that exposed carpeting can be disinfected by simple cleaning methods. The first step is routine vacuuming of carpets to remove hairs from the surface of the carpet. This will help prevent them from being entangled in the fibers. Chemical-free decontamination of carpets can be achieved by repeat cleaning of carpets using a carpet shampooer or hot water extraction and is the most reasonable recommendation for a home situation where this is needed. In high-risk situations or where a high level of decontamination is needed, necessary carpeting can be pretreated with a disinfectant prior to cleaning. Disinfectants with a label claim of efficacy for treating Trichophyton species are recommended as first-choice options. This study found supporting evidence for potassium peroxymonosulfate for carpet decontamination.