Infection Prevention and Control/Surface Decontamination

Ultraviolet Surface Disinfection for SARS-CoV-2

Ultraviolet Germicidal Irradiation

UV-C air disinfection was been explored extensively in the context of TB infection prevention and control by the South African scientific community in association with international experts. National Technical Standards, Protocols, guidelines and testing capacity for application of upper-room UVGI in airborne transmission have been established. This experience has provided important basic knowledge and key insights into the underpinning science and theory as well as application constraints, albeit for a different application.

Introduction

The coronavirus, SARSs-CoV-2, is understood to be transmitted primarily by contact and droplet spread.

Covid-19 is highly contagious and spreads more rapidly than its predecessors Severe Acute Respiratory Syndrome (SARS-Cov-1) and Middle East Respiratory Syndrome (MERS)</ref>, so any residual contamination can pose a public health threat. COVID-19 transmission remains controversial as researchers across the globe remain conflicted about droplet and airborne as modes of transmission. Clarifying the transmission routes and survival of viruses on frequently used surfaces is essential for containment of the outbreak. Research has successfully demonstrated that the virus has the potential to be aerosolised, and therefore can theoretically opportunistically transmit through the airborne route, it is understood that, except in aerosolising procedures, risk of coronavirus transmission via the airborne route is low. Similarly, risk via water and wastewater is low . Persistence of the virus on a variety of surfaces has been demonstrated , underpinning concern that SARS-CoV-2 may be transmitted from infected (even asymptomatic) persons to others from touching common surfaces, even after the infector has departed for several hours . Efforts to contain the coronavirus, to stem the pandemic, should therefore primarily focus on contact and droplet transmission. Contact and droplet transmission is of concern in public transport systems taxis which convey very large transient populations is normally congested conditions, such as in trains and mini-bus taxis. Transfer of suspected or confirmed Covid-19 patients in planned transport or emergency service vehicles poses a risk since studies show that conventional decontamination procedures may be inadequat. In a pandemic, and within already constrained healthcare infrastructure, overcrowding and close proximity of infectious and susceptible individuals will become highly. These conditions will amplify the risk of Covid-19 transmission.

In the South African context, the reduction of exposure to Covid-19 is a priority, in order to:

• reduce and delay occupational exposure of frontline workers especially healthcare and transport services workers;
• reduce exposure to public health risk, especially to the most vulnerable, such as PLHIV and persons with TB who are the principal users of public transport;
• contribute to the strategy of “flattening the curve”; and
• preserve and protect the healthcare service so as to ensure continued service.

This article proposes UV-C surface disinfection for reducing contact and droplet transmission of SARS-CoV-2 through the following applications:

1. Portable disinfection devices for use in the transport sector (minibus taxis, trains and emergency and planned patient transport)
2. Public Spaces
3. Commercial and industrial occupational settings
4. Decontamination of personal and respiratory protection equipment

UV-C: potential for disinfection for SARS-CoV-2

The disinfection effect of ultraviolet light has been described for over 100 years. It is effective against a variety of microorganisms and has been successfully deployed for the purpose of disinfection of water, air and surfaces. Effectiveness depends on a range of variables related to the microorganism of interest, environment and application. Ultraviolet radiation in the UV-C range has been used for its germicidal properties specifically for infection prevention and control - have been demonstrated to work at laboratory scale, in ducts, as upper room irradiation and as portable devices. Safety guidelines have been established (ACGIH). There is good reason to expect that SARS-CoV-2 will be susceptible to UV-C. UV-C, when applied at the correct dose as it has been found effective against influenza viruses including human coronavirus (SARS-CoV-1).

According to Kowalski et. al. , Covid-19 is susceptible to existing disinfection methods such as chemicals and exposure to ultraviolet radiation in the electromagnetic range ~ 200 – 280nm (UV-C) because of the similarity of its structure to other susceptible coronaviruses such as SARS-CoV-1 and MERS.

UVGI surface disinfection has advantages over chemical disinfection because:

• There is no off-gassing of chemicals or residual chemical contamination frequently associated with chemical-based disinfection methods. Therefore, vehicles or spaces can be occupied immediately after UVGI disinfection;
• It has high pathogen reduction rates when compared to chemical cleaning; and
• Chemical disinfection methods are time-consuming .

A guideline on hospital infection control recommends the use of both UVGI and chemical disinfection since UVGI has no penetrating power on dust, dirt and grease, which may harbour microbial contamination. Exposure to UV-C may degrade some materials.

As SARS-CoV-2 is recent and novel, UVGI efficacy has not yet been conclusively established against this particular pathogen. For the reasons stated above, UVGI – the exposure of potentially contaminated contact surfaces to UV-C is identified as a measure with good prospects to reduce and delay occupational exposure of healthcare and transport services workers, as well as their clientele, and to contribute to the strategy of “flattening the curve”.

Approaches to UVGI surface disinfection

The application of UVGI for surface disinfection usually involves the use of bare UVGI lamps. Two main approaches to surface disinfection systems are via permanently installed disinfection systems and portable disinfection systems. Permanently installed systems generally consist of bare UVGI lamp fixtures mounted on ceilings or walls. Portable UVGI systems are moved into a place temporarily to decontaminate surfaces . Efficacy is dependent on the intensity of irradiation emitted from the device, proximity of the device to the surface being disinfected and exposure time. The reflectivity of the materials in the vicinity of exposure can increase or decrease efficacy. Shaded items not directly exposed to UV-C irradiation may not effectively be disinfected

Case Studies

Moscow trains

In Moscow, Russia, Kostyuchenko, et. al., , investigated the potential of UVGI disinfection on internal surfaces of train carriages and on escalator handrails. They found that the required UV doses for effective disinfection are higher than the theoretically calculated doses.

Elements of a successful UVGI Disinfection Program

Messaging

It is important for messaging around a UVGI Disinfection Program to detail that UVGI can be safe and effective when applied according to a defined and validated protocol

The messaging program should include the following safety aspects:

• UVGI is a form of actinic radiation which does not cause skin cancer
• UVGI/UVC is not the same as UV found in outdoor sunlight
• UVGI can cause reversible skin and eye irritation
• Skin and eye protection should be worn when the possibility of irradiation is present
  
• UV Lamps should not be used for skin or hand sterilisation

The messaging program should include the following efficacy aspects:

• UVGI is a supplemental surface disinfection technology
• UVGI can be used to kill the new coronavirus as well as a number of other common pathogens

Efficacy

Surface UVGI dose requirements

The UV-C dose required to achieve a particular pathogen reduction rate is calculated from the single-stage decay equation:

S=e^-kD

where:

• S is the Survival fractional [%]
  
• k is the UVGI rate constant [m2/J]
  
• D is the UVGI exposure dose [J/m2]
  

In the absence of a specific UVGI rate constant for SARS-CoV-2, Kowalski et. al. have proposed an average value for the calculation of the required dose. The average rate constant from recent Coronavirus studies is shown in the table below.

Summary of Recent Ultraviolet Studies on SARs Coronavirus -

Microbe	D90 Dose J/m2 (J/cm2)	Uv k [m2/J]
SARS Coronavirus CoV-P9	40 (0.04)	0.05750
SARS Coronavirus (Hanoi)	134 (0.134)	0.01720
SARS Coronavirus (Urbani)	241 (0.241)	0.00955
Average	138 (0.138)	0.02808

The required UVGI dose for SARS-CoV-2 for a 4 log reduction (99.99% pathogen reduction rate) is calculated by expressing the single-stage decay equation as follows: ln⁡S=-k'D ln⁡e

∴D = ln ⁡0.0001/(-0.02828) = 328 mJ/cm² (0.328 J/cm²)

Validated UV dose testing

Validation testing for UVGI surface disinfecting systems is required to ensure that the UV dose for ≥99.99% level of pathogen inactivation is achieved. As the dose rate is a function of the UV sources output and its distance to the target, the manufacturer for non-static UVGI surface disinfecting systems should specify the design minimum distance away from a surface, the UVGI intensity on the surface and the time required to achieve ≥99.99% pathogen reduction.

Safety

Studies [17, 18] of personnel practising proper UVGI exposure control measures have shown no harmful effects. Noncompliance with safety precautions can lead to injuries [18]. The following safety issues are associated with the handling of UV equipment.