Bridging the gap: Establishing UV claims for emerging pathogens

The following content is sponsored by Clorox



Recently, there has been an increased focus in many healthcare facilities on preventing the spread of emerging pathogens, especially those that are resistant to antimicrobial drugs. These emerging infection risks have also made it more and more important for facilities to develop and implement emergency preparedness plans to both isolate and treat symptomatic patients while safeguarding the hospital staff and larger community. However, for those healthcare facilities that wish to adopt a more comprehensive approach to environmental infection control, there is little guidance on how to incorporate a bundled approach of manual disinfectants and ultraviolet treatment.

The Centers for Disease Control and Prevention and U.S. Environmental Protection Agency developed a recommended approach to help bridge the gap between disinfectant efficacy claims for common healthcare-associated pathogens and emerging pathogens.[i],[ii],[iii] The aim of this approach is to help healthcare professionals choose appropriate manual disinfectants for use against emerging pathogens when no disinfectants with EPA-registered claims are available. This article will outline the CDC and EPA approach and how it can be extended to provide guidance for the use of supplemental UV devices in an environmental protection strategy against emerging pathogens.

Manual environmental cleaning & disinfection approach for emerging pathogens

For emerging pathogens or pathogens that are hard to isolate or handle safely in the laboratory, such as the Ebola virus, there often is no regulatory pathway to obtain an EPA-registered sanitization or disinfection claim. In this case, a new microbiological analysis protocol must be developed following EPA guidelines.[iv] However this is a time-consuming process that sometimes involves using a surrogate organism to represent the target pathogen to reduce safety risks and deliver an organism for test purposes.[v] This waiting period can leave hospital infection control teams at a loss when trying to determine appropriate disinfectants for use in the interim.

When an emerging pathogen poses a significant public health risk, the CDC and EPA guidance is intended to bridge the gap by identifying disinfectant products that may be used while effective test protocols are being developed. The approach draws on well-established pathogen hierarchy and efficacy data, in addition to peer-reviewed studies. Table I below shows the EPA-recognized pathogen hierarchy for the selection of disinfectants to be used against emerging pathogens. This hierarchy ranks classes of microorganisms by order of their relative susceptibility to hard surface disinfectants,[vi] with the hardest pathogens to kill (bacterial endospores) at the top of the list and the organisms most susceptible to disinfectants at the bottom.  

Table I
Pathogen Hierarchy[vii]
Descending order of resistance to germicidal chemicals

Bacterial Spores
(Bacillus subtilis, Clostridium sporogenes)

(Mycobacterium tuberculosis var. bovis, Nontuberculous mycobacteria)

Nonlipid, Non-enveloped, or Small Viruses
(Poliovirus, Coxsackievirus, Rhinovirus)

(Trichophyton, Cryptococcus, Candida spp.)

Vegetative bacteria
(P. aeruginosa, S. aureus, S. choleraesuis, Enterococci)

Lipid, Enveloped, or medium-sized viruses
(Herpes simplex, Cytomegalovirus, RSV, Hepatitis B, Hepatitis C, HIV, Hantavirus, Ebola virus)

Using this pathogen hierarchy and the wealth of micro-efficacy testing data for EPA-registered disinfectants, the CDC developed recommendations specifically for the Ebola virus.[viii] Though the Ebola virus is an enveloped virus, the CDC recommends the use of EPA-registered hospital disinfectants with kill claims against harder-to-kill non-enveloped viruses in order to disinfect rooms of patients with suspected or confirmed Ebola virus disease. The same approach can be applied to develop recommendations for other emerging pathogens as well.  

Applying the "bridge the gap" approach to UV devices

It is well documented that UV-C light, a high energy form of ultraviolet light, is a highly effective germicide[ix],[x] – so well, in fact, that Kowalski's UV handbook states that "given sufficient exposure time, any exposed pathogen can be inactivated."[xi] Thus, similar to the CDC's pathogen hierarchy for manual disinfectants, examining the UV pathogen hierarchy is a good starting point when determining if a specific device has the potential to support a claim against emerging pathogens.

The generalized UV pathogen hierarchy adapted from the "Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection" (shown in Table II), provides guidance on the microbial susceptibility to UV-C light among various organism species. The hierarchy of susceptibility to UV-C light is notably different than that referenced for chemical manual disinfectants. In general with UV-C, vegetative bacteria are easier to inactivate, and fungi require the highest UV-C dosage for inactivation. Interestingly, bacterial spores such as Clostridium difficile, which are known for their environmental persistence, are intermediate on the UV Dose Hierarchy.

Table II
Generalized UV-C Dose Hierarchy[xii]
Listed by Decreasing Inactivation Difficulty

Fungal Spores

Fungal Cells/Yeast

Bacterial Spores


Vegetative Bacteria

Clorox UV

Beyond this hierarchy, there is a wealth of data available on the UV dosage required for inactivation of specific pathogens. However, unlike manual surface disinfectants, the EPA does not currently provide a route for obtaining EPA-registered kill claims using UV germicidal irradiation.

UV dosages for non-enveloped viral pathogens such as adenovirus, norovirus, poliovirus, and rotavirus range from 18,000-84,000 μw-sec/cm² for a 2-log kill.[xiii],[xiv] In comparison, the UV dosage required to inactivate enveloped Ebola virus is significantly less – 2000[xv]-5300[xvi] μw-sec/cm² for a 2-log kill. Historically, UV doses have been listed by either their D90 (90 percent inactivation) or D99 values (2-log reduction).  In order to address the more stringent needs for healthcare applications, 3-4 log reductions (99.9 percent -99.99 percent microbial kill) or greater are typically obtained for target microorganisms and validated via laboratory testing. Comparisons of known and predicted pathogen doses can be used to determine the effectiveness of a UV-C device at a given exposure time and distance.

Current limitations for UV microorganism efficacy testing

Since there are no EPA-approved protocols to validate micro-efficacy claims for UV devices, the industry faces a lack of standardized test methods and oversight on the claims made by device manufacturers. Thus manufacturers generate data using different test methods, making it difficult to compare efficacy claims from one device to another for pathogens.

Device manufacturers that generate micro-efficacy data should show full transparency about the test conditions used, such as the irradiation time, distance, substrate, carrier load, and density as well as for the log reductions obtained.

Building the case for a comprehensive bundled approach: Manual disinfection supplemented by UV-C devices

In light of the dangers posed by emerging pathogens, many hospitals are interested in emerging technologies such as UV-C technology to reduce transmission to patients and protect their staff. UV devices can add an extra layer of assurance when it comes to terminal cleaning; reaching areas of the healthcare environment that may otherwise be missed or insufficiently addressed due to human error. However manual disinfection is still essential for removing soils and killing pathogens on environmental surfaces and plays an important role in infection prevention protocols.

A key finding of the 2011 study by Sagripanti and Lytle in the Archives of Virology[xvii] and work by Bausch published in The Journal of Infectious Diseases[xviii] is that environmental conditions can impact the effectiveness of pathogen inactivation via UV devices. The presence of organic matter, such as dried blood, can shield the pathogen from the UV-C light and reduce the treatment's effectiveness. In addition, studies have shown that only 50 percent of high-risk surfaces in healthcare settings are properly cleaned[xix]. These studies further illustrate the need for the use of appropriate manual disinfection prior to UV-C treatment. UV-C room treatment serves to supplement, not replace, standard cleaning and disinfection protocols[xx] and provides another weapon in the battle against pathogens that cause healthcare-associated infections.

As healthcare facilities strive to identify novel solutions to meet the infection control challenges posed by emerging pathogens, it is important to remember how to "bridge the gap" to determine which disinfectants and UV devices can be used based on EPA-registered efficacy claims. This can be done by consulting known pathogen hierarchies, micro-efficacy data and peer-reviewed studies, and by applying principles set by the CDC and EPA to understand how to address dangerous emerging pathogens.

For information about Clorox Healthcare™ Optimum-UV™ System, a comprehensive bundled approach for environmental infection control, as well as information about emerging pathogens and HAIs, visit


[i] Centers for Disease Control and Prevention. "Interim Guidance for Environmental Infection Control in Hospitals for Ebolavirus." 1 August 2014.

[ii] US Environmental Protection Agency. "Implementation of the Emerging Pathogens and Disinfection Hierarchy for Antimicrobial Products." 3 April 2008.

[iii] Centers for Disease Control and Prevention. "Severe Respiratory Illness Associated with Enterovirus D68 – Multiple States, 2014." Official CDC Health Advisory. 12 September 2014.

[iv] The FEM Microbiology Action Team. "Method Validation of U.S. Environmental Protection Agency Microbiological Methods of Analysis." The EPA Forum on Environmental Measurements (FEM) . FEM Document Number 2009-01. 7 October 2009.

[v] Sinclair, R.G. et al. "Criteria for Selection of Surrogates Used to Study the Fate and Control of Pathogens in the Environment." Appl Environ Microbiol. 78.6 (2012): 1969-1977.

[vi] US Environmental Protection Agency. "Implementation of the Emerging Pathogens and Disinfection Hierarchy for Antimicrobial Products." 3 April 2008.

[vii]             b. As referenced by the EPA: Spaulding, E.H. "Chemical disinfection of medical and surgical materials." Disinfection, Sterilization, & Preservation, 3rd Edition., Block, S. (Ed). Philadelphia: Lea & Febiger, 1968. 517-31.

                c. See also: Favero, M.S., Bond, W.W. "Chemical disinfection of medical and surgical materials." Disinfection, Sterilization, & Preservation, 5th Edition. Block, S. (Ed). Philadelphia: Lippincott Williams & Wilkins, 2001. 888 (Table 43.2)..

[viii] Centers for Disease Control and Prevention. "Interim Guidance for Environmental Infection Control in Hospitals for Ebolavirus." 1 August 2014.

[ix] Kowalski, W. Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection. Springer, 2009.

[x] Bolton, J.R., C.A. Cotton. The Ultraviolet Disinfection Handbook. American Water Works Association, 2008.

[xi] Kowalski, W. Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection. Springer, 2009. 467.

[xii] Adapted from W. Kowalski, Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection, Springer, 2009. 75.

[xiii] For example: Kowalski, W. Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection. Springer, 2009. Appendices A, B, C.

[xiv] The response to UV exposure is often described in terms of UV inactivation dosage or UV rate constants. For example, the UV dose required to inactivate 99% of the organism (2 log kill) is referred to as the D99 dose. UV Doses are typically listed by either their D90 (90% inactivation) or D99 values, and different sources use different units (i.e., J/m2, μW-sec/cm², or mw-sec/cm²) for the dose, so care must be taken when comparing referenced dose values. In general, the D99 value is approximately twice the value listed for D90.  

[xv] Sagripanti, J.L., Lytle, D.C. "Sensitivity to ultraviolet radiation of Lassa, vaccinia, and Ebolaviruses dried on surfaces." Arch Virol 156 (2011): 489–494.

[xvi] Kowalski, W.J. Internal UVDI/Clorox Communication.

[xvii] Sagripanti, J.L., Lytle, D.C. "Sensitivity to ultraviolet radiation of Lassa, vaccinia, and Ebolaviruses dried on surfaces." Arch Virol 156 (2011) : 489–494.

[xviii] Bausch, D.G. et al. „"Assessment of the Risk of Ebolavirus Transmission from Bodily Fluids and Fomites." J Infect Dis 196 (2007): S142–7.

[xix] Carling, P.C., Parry, M.M., Rupp, M.E., Po, J.L., Dick, B., Von Beheren, S., Healthcare Environmental Hygiene Study Group. "Improving Cleaning of the Environment Surrounding Patients in 36 Acute Care Hospitals." Infection Control and Hospital Epidemiology 29.11 (2008): 1035-41.

[xx] Memarzadeh, F. et al. "Applications of ultraviolet germicidal irradiation disinfection in health care facilities: Effective adjunct, but not stand-alone technology." Am J Infect Control 38 (2010): S13-24.

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