Ex vivo protocol for testing virus survival on human skin: experiments with herpesvirus 2

Survival of SARS-CoV-2 and influenza virus on the human skin: Importance of hand hygiene in COVID-19

Background

The stability of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on human skin remains unknown, considering the hazards of viral exposure to humans. We generated a model that allows the safe reproduction of clinical studies on the application of pathogens to human skin and elucidated the stability of SARS-CoV-2 on human skin.

Methods

We evaluated the stability of SARS-CoV-2 and influenza A virus (IAV), mixed with culture medium or upper respiratory mucus, on human skin surfaces and the dermal disinfection effectiveness of 80% (weight/weight) ethanol against SARS-CoV-2 and IAV.

Results

SARS-CoV-2 and IAV were inactivated more rapidly on skin surfaces than on other surfaces (stainless steel/glass/plastic); the survival time was significantly longer for SARS-CoV-2 than for IAV (9.04 hours [95% confidence interval, 7.96– 10.2 hours] vs 1.82 hours [1.65–2.00 hours]). IAV on other surfaces was inactivated faster in mucus versus medium conditions, while SARS-CoV-2 showed similar stability in the mucus and medium; the survival time was significantly longer for SARS-CoV-2 than for IAV (11.09 hours [10.22–12.00 hours] vs 1.69 hours [1.57–1.81 hours]). Moreover, both SARS-CoV-2 and IAV in the mucus/medium on human skin were completely inactivated within 15 seconds by ethanol treatment.

Conclusions

The 9-hour survival of SARS-CoV-2 on human skin may increase the risk of contact transmission in comparison with IAV, thus accelerating the pandemic. Proper hand hygiene is important to prevent the spread of SARS-CoV-2 infections.

Transfer of Enteric Viruses Adenovirus and Coxsackievirus and Bacteriophage MS2 from Liquid to Human Skin

Enteric viruses (viruses that infect the gastrointestinal tract) are responsible for most water-transmitted diseases. They are shed in high concentrations in the feces of infected individuals, persist for an extended period of time in water, and are highly infective. Exposure to contaminated water directly (through ingestion) or indirectly (for example, through hand-water contacts followed by hand-to-mouth contacts) increases the risk of virus transmission. The work described herein provides a quantitative model for estimating human-pathogenic virus retention on skin following contact with contaminated water. The work will be important in refining the contribution of indirect transmission of virus to risks associated with water-related activities.

Indirect exposure to waterborne viruses increases the risk of infection, especially among children with frequent hand-to-mouth contacts. Here, we quantified the transfer of one bacteriophage (MS2) and two enteric viruses (adenovirus and coxsackievirus) from liquid to skin. MS2, a commonly used enteric virus surrogate, was used to compare virus transfer rates in a volunteer trial to those obtained using human cadaver skin and synthetic skin. MS2 transfer to volunteer skin was similar to transfer to cadaver skin but significantly different from transfer to synthetic skin. The transfer of MS2, adenovirus, and coxsackievirus to cadaver skin was modeled using measurements for viruses attaching to the skin (adsorbed) and viruses in liquid residual on skin (unadsorbed). We find virus transfer per surface area is a function of the concentration of virus in the liquid and the film thickness of liquid retained on the skin and is estimable using a linear model. Notably, the amount of MS2 adsorbed on the skin was on average 5 times higher than the amount of adenovirus and 4 times higher than the amount of coxsackievirus. Quantification of pathogenic virus retention to skin would thus be overestimated using MS2 adsorption data. This study provides models of virus transfer useful for risk assessments of water-related activities, demonstrates significant differences in the transfer of pathogenic virus and MS2, and suggests cadaver skin as an alternative testing system for studying interactions between viruses and skin.

IMPORTANCE Enteric viruses (viruses that infect the gastrointestinal tract) are responsible for most water-transmitted diseases. They are shed in high concentrations in the feces of infected individuals, persist for an extended period of time in water, and are highly infective. Exposure to contaminated water directly (through ingestion) or indirectly (for example, through hand-water contacts followed by hand-to-mouth contacts) increases the risk of virus transmission. The work described herein provides a quantitative model for estimating human-pathogenic virus retention on skin following contact with contaminated water. The work will be important in refining the contribution of indirect transmission of virus to risks associated with water-related activities.

Methods to evaluate the microbicidal activities of hand-rub and hand-wash agents

In vitro carrier tests, suspension tests, time-kill curves, and determinations of minimum inhibitory concentrations to evaluate the microbicidal activities of hand antiseptics provide only a preliminary indication of the antimicrobial spectrum and speed of action of a given formulation. Ex vivo testing with human or animal skin at human skin temperature and at contact times reflecting field conditions may give a better indication of a formulation's ability to tackle hand-transmitted pathogens. Field testing of hands for levels of skin microbiota before and after antisepsis may be easier to perform, but it is subject to many uncontrollable factors. Whereas randomised clinical trials may be the ultimate approach to assess the effectiveness of hand hygiene protocols and products in preventing microbial cross-transmission and, ultimately, infections, they can be prohibitively expensive, time-consuming, difficult to design, and therefore impractical. Hence, the primary emphasis should be on in vivo testing on human hands, using a well-designed protocol that closely simulates the recommended field use of the formulation, and possibly followed by clinical studies. The use of these method is the most likely to yield useful data on the potential of a formulation to interrupt the spread of pathogens transmitted by hands in healthcare settings. This review provides a critical assessment of the methods currently used to meet regulatory requirements for hand antiseptics in Europe and North America.

A new Sephadex-based method for removing microbicidal and cytotoxic residues when testing antiseptics against viruses: Experiments with a human coronavirus as a model

The relative lack of efficient methods for evaluating antiseptic antiviral activity, together with weaknesses in the existing European Standard (i.e. NF EN 14476+A1), underlines the need to seek a new method which could allow a more precise evaluation of the antiseptic antiviral activity of chemical agents.

This protocol is based on an original gel-based filtration method, using “in-house” G-25 and G-10 Sephadex™ columns. This method allows the neutralization of both the activity and the cytotoxicity of a large range of molecules, according to their molecular size, in only 1 min.

The viral model used was the human coronavirus (HCoV) 229E chosen for (i) its increasing medical interest, (ii) its potential resistance and (iii) its representing enveloped viruses mentioned in the European Standard.

First, the protocol was validated and it was demonstrated that it was fully operational for evaluating antiviral antiseptic potentiality and useful to screen potentially antiseptic molecules.

Second, chlorhexidine (CHX) and hexamidine (HXM) were assessed for their potential anti-HCoV 229E antiseptic activities. It was demonstrated clearly that (i) HXM had no activity on the HCoV 229E and (ii) CHX showed a moderate anti-HCoV 229E activity but insufficient to be antiseptic.

Ex vivo stability of the rodent-borne Hantaan virus in comparison to that of arthropod-borne members of the Bunyaviridae family

The possible effect of virus adaptation to different transmission routes on virus stability in the environment is not well known. In this study we have compared the stabilities of three viruses within the Bunyaviridae family: the rodent-borne Hantavirus Hantaan virus (HTNV), the sand fly-borne Phlebovirus sandfly fever Sicilian virus (SFSV), and the tick-borne Nairovirus Crimean-Congo hemorrhagic fever virus (CCHFV). These viruses differ in their transmission routes: SFSV and CCHFV are vector borne, whereas HTNV is spread directly between its hosts, and to humans, via the environment. We studied whether these viruses differed regarding stability when kept outside of the host. Viral survival was analyzed at different time points upon exposure to different temperatures (4 degrees C, 20 degrees C, and 37 degrees C) and drying at 20 degrees C. We observed clearly different stabilities under wet conditions, particularly at 4 degrees C, where infectious SFSV, HTNV, and CCHFV were detectable after 528, 96, and 15 days, respectively. All three viruses were equally sensitive to drying, as shown by drying on aluminum discs. Furthermore, HTNV and SFSV partially survived for 2 min in 30% ethanol, whereas CCHFV did not. Electron microscopy images of HTNV, SSFSV, and CCHFV stored at 37 degrees C until infectivity was lost still showed the occurrence of virions, but with abnormal shapes and densities compared to those of the nonincubated samples. In conclusion, our study points out important differences in ex vivo stability among viruses within the Bunyaviridae family.

Use of the 'ex vivo' test to study long-term bacterial survival on human skin and their sensitivity to antisepsis

AIMS

To determine bacterial survival on human skin and their sensitivity to antisepsis.

METHODS AND RESULTS

An 'ex vivo' protocol which uses human skin samples placed into diffusion cells, and electron microscopy (EM), were used to study the growth of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa inoculated onto skin samples over a 46-h incubation period at 32 degrees C. Concurrently variation in skin pH was evaluated at different time intervals during this period. In addition the antimicrobial activity of three antiseptics against the incubated micro-organisms was assessed quantitatively with the 'ex vivo' test, while their detrimental effects against bacteria were observed by EM. All three bacteria were still present in high number after 46 h inoculation on skin, although the concentration of E. coli and S. aureus were reduced by 2.74 and 1.58 log(10) reduction, respectively, over this period of time. Electron micrographs showed clear evidence of cell division and some bacteria appeared to be embedded into the skin layers. The antiseptics tested had some antibacterial activity against bacteria incubated on skin for 3 and 10 h, and EM evidence showed some morphological damages including cellular blebbing and the presence of fibrillar material around the cells. All micro-organisms had an acidifying effect on skin samples.

CONCLUSIONS

Here, it was shown that bacterial pathogens can survive and grow when incubated on human skin. In addition, it is possible that they can penetrate the stratum corneum, which can provide some protection against antisepsis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The apparent low bactericidal activity of biocides attributed in part to bacterial protection from skin layers is particularly important to assess in order to ensure antisepsis efficacy.

Short- and long-term effects of handwashing with antimicrobial or plain soap in the community

Little is known about effects of public use of antimicrobial handwashing soap. A double-blinded, randomized clinical trial of hands of primary caretakers in 238 inner city households was conducted in which effects of plain or antimicrobial (containing 0.2% triclosan) handwashing soap on bacterial counts of the hands were compared before and after a single wash and before and after handwashing following a year of product use. The randomly assigned product was provided without cost to each household during monthly home visits, and compliance with product use was monitored. Households were contacted by telephone weekly and with a home visit monthly for 11 months. Hand cultures were obtained before and after handwashing at baseline and after 11 months, using a modified glove juice technique. Overall, there were no significant differences in pre-to-post handwashing counts at baseline (p = 0.41), but by the end of one year, post-wash counts were significantly lower than pre-wash (p = 0.000) for those using either antimicrobial or plain soap. There were no significant differences in mean log counts either before or after handwashing between those using the antimicrobial or plain soap at baseline or after a year of use (all p values > 0.28). For the group using antimicrobial soap, higher counts were observed post-handwashing in 31.3% of paired samples at baseline and 26.7% after one year (p = 0.03). A single handwash had minimal effect on quantity of hand flora, but there were significant effects over time, regardless of whether antimicrobial or plain soap was used. In the absence of more definitive evidence, the risk-benefit ratio argues in favor of targeted rather than ubiquitous, general household use of antimicrobial soap.

Hygienic hand antiseptics: should they not have activity and label claims against viruses?

Enteric and respiratory viruses are among the most frequent causes of human infections, and hands play an important role in the spread of these and many other viral diseases. Regular and proper hand hygiene by caregivers and food handlers in particular is essential to decontaminate hands and potentially interrupt such spread. What would be considered a proper decontamination of hands? Handwashing with regular soap and water is often considered sufficient, but what of hygienic handwash and handrub antiseptic products? Are they more effective? The evidence suggests that some clearly are. Activity against bacteria may not reflect the ability of hygienic hand antiseptics to deal with viruses, especially those that are nonenveloped. In spite of the acknowledged importance of hands as vehicles for viruses, there is a lack of suitable regulatory mechanism for handwash or handrub products to make claims of efficacy against viruses. This is in contrast with the ability of general-purpose disinfectants to make antiviral claims, although transmission of viruses from surfaces other than those of reusable medical devices may play only a minor role in virus transmission. This review discusses the (1). recent information on the relative importance of viruses as human pathogens, particularly those causing enteric and respiratory infections; (2). the survival of relevant viruses on human hands in comparison with common gram-negative and gram-positive bacteria; (3). the potential of hands to transfer or receive such contamination on casual contact; (4). role of hands in the spread of viruses; (5). the potential of hygienic measures to eliminate viruses from contaminated hands; (6). relative merits of available protocols to assess the activity of hygienic hand antiseptics against viruses; and (7). factors considered crucial in any tests to assess the activity of hygienic hand antiseptics against viruses. In addition, this review proposes surrogate viruses in such testing and discusses issues for additional consideration by researchers, manufacturers, end-users, and regulators.

A quantitative study of the survival of two species of Candida on porous and non-porous environmental surfaces and hands

AIMS

In spite of the importance of many species of Candida as human pathogens, little is known about their ability to survive on animate and inanimate surfaces. Such information is essential in understanding the vehicles and modes of their spread, and in designing proper infection control strategies against them. The aim of this study was to generate comparative quantitative data in this regard.

METHODS AND RESULTS

The survival of one clinical isolate each of Candida albicans and C. parapsilosis on two types of hard inanimate surfaces (glass and stainless steel) and two types of fabrics (100% cotton and a blend of 50% cotton and 50% polyester) was evaluated under ambient conditions (air temperature 22 +/- 2 degrees C; relative humidity 45-62%) using quantitative test protocols. The survival of C. albicans was also assessed on human skin, using the fingerpads of adult volunteers as carriers. Each carrier surface received 10 microl of the test suspension containing a soil load to simulate body fluids. When dried on glass and stainless steel carriers, C. albicans and C. parapsilosis remained viable for at least three and 14 days, respectively. Both species could survive for at least 14 days on both types of fabric. On the skin, 20% of the viable C. albicans remained detectable one hour post-inoculation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This quantitative and comparative study demonstrated the potential for, and differences in the ability of clinically significant species of Candida to remain viable on porous and non-porous inanimate surfaces as well as on human hands. These results should help in understanding the epidemiology of nosocomial infections due to Candida, and in designing better prevention and control strategies against them.

Transfer of bacteria from fabrics to hands and other fabrics: development and application of a quantitative method using Staphylococcus aureus as a model

AIMS

To develop and apply a quantitative protocol for assessing the transfer of bacteria from bleached and undyed fabrics of 100% cotton and 50% cotton + 50% polyester (poly cotton) to fingerpads or other pieces of fabric.

METHODS AND RESULTS

Test pieces of the fabrics were mounted on custom-made stainless steel carriers to give a surface area of 1 cm in diameter, and each piece seeded with about 10(5) cfu of Staphylococcus aureus from an overnight broth culture; the inoculum contained 5% fetal bovine serum as the soil load. Transfer from fabric to fabric was performed by direct contact using moist and dry fabrics. Transfers from fabrics to fingerpads of adult volunteers were tested using moist, dry and re-moistened pieces of the fabrics, with or without friction during the contact. Bacterial transfer from fabrics to moistened fingerpads was also studied. All the transfers were conducted under ambient conditions at an applied pressure of 0.2 kg cm(-2). After the transfer, the recipient fingerpads or fabric pieces were eluted, the eluates spread-plated, along with appropriate controls, on tryptic soy agar and the percentage transfer calculated after the incubation of the plates for 24 h at 37 degrees C.

CONCLUSION

Bacterial transfer from moist donor fabrics using recipients with moisture was always higher than that to and from dry ones. Friction increased the level of transfer from fabrics to fingerpads by as much as fivefold. Bacterial transfer from poly cotton was consistently higher when compared with that from all-cotton material.

SIGNIFICANCE AND IMPACT OF THE STUDY

The data generated should help in the development of better models to assess the role fabrics may play as vehicles for infectious agents. Also, the basic design of the reported methodology lends itself to work with other types of human pathogens.

Preventing the spread of hepatitis B and C viruses: where are germicides relevant?

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are the most prevalent bloodborne pathogens. Infections caused by these organisms can become chronic and may lead to liver cirrhosis and carcinoma. Limited chemotherapy is now available, but only HBV can be prevented through vaccination. Both viruses are enveloped and relatively sensitive to many physical and chemical agents; their ability to survive in the environment may not be as high as often believed. As a result, their spread occurs mainly through direct parenteral or percutaneous exposure to tainted body fluids and tissues. Careful screening of and avoiding contact with such materials remain the most effective means of protection. Nevertheless, the indirect spread of these viruses, although much less common, can occur when objects that are freshly contaminated with tainted blood enter the body or contact damaged skin. Germicidal chemicals are important in the prevention of HBV and HCV spread through shared injection devices, sharps used in personal services (such as tattooing and body piercing), and heat-sensitive medical/dental devices (such as flexible endoscopes) and in the cleanup of blood spills. Microbicides in vaginal gels may also interrupt their transmission. General-purpose environmental disinfection is unlikely to play a significant role in the prevention of the transmission of these viruses. Testing of low-level disinfectants and label claims for such products against HBV and HCV should be discouraged. Both viruses remain difficult to work with in the laboratory, but closely related animal viruses (such as the duck HBV) and the bovine viral diarrhea virus show considerable promise as surrogates for HBV and HCV, respectively. Although progress in the culturing of HBV and HCV is still underway, critical issues on virus survival and inactivation should be addressed with the use of these surrogates.

A mathematical model describing the thermal virus inactivation

A new mathematical model is proposed to describe the inactivation of viruses at different temperatures. This model takes into account the exponential decrease of the viral titer with time, the inactivation rate being an exponential function of the temperature. A one-step non-linear regression was used to fit oral poliovirus vaccine (OPV) experimental data. In one of the applications of the model, we illustrate the use of our model to compare the accelerated degradation test of OPV new formulations to standard OPV. Such a model is both simple and convenient to use. It should be a useful tool in optimizing formulations for live viral vaccines.