Nosocomial or healthcare-acquired infections (HAIs) are infections that originate within a healthcare setting. These infections can cause significant morbidity and mortality in patients.
HAIs are also known to hold a significant financial burden for healthcare systems. The emergence of the coronavirus disease 2019 (COVID-19) pandemic has increased this burden in healthcare facilities throughout the world.
Study: Brought to Light: How Ultraviolet Disinfection Can Prevent the Nosocomial Transmission of COVID-19 and Other Infectious Diseases. Image Credit: Nor Gal / Shutterstock.com
Background
The most common nosocomial pathogens known are either viruses or bacteria. Although there are a plethora of antibiotics that are available for use, antibiotic resistance, as well as the inability of these compounds to treat viral infections, limits the utility of this treatment option.
These pathogens are therefore capable of surviving on surfaces for years and can be transmitted to people within healthcare facilities. The highest risk to the healthcare system is posed by diseases that are difficult to treat; therefore, the prevention of diseases caused by these pathogens is of great importance.
Effective cleaning of surfaces is considered to be essential in preventing the transmission of pathogens. However, several studies have indicated that less than 50% of surfaces in patients' rooms are cleaned effectively, thus allowing these rooms to become environmental reservoirs that can infect subsequent patients.
Enhanced environmental cleaning needs to be considered to prevent the transmission of HAIs. Manual cleaning is not sufficient; therefore, novel disinfection strategies must be considered to prevent diseases caused by pathogens, especially those that are difficult to treat.
A new review article published in Applied Microbiology determines the role of ultraviolet (UV) disinfection for nosocomial transmission of COVID-19 and other infectious diseases.
Mechanism of viral mutation
The mutation of viruses is an important factor that contributes to the spread of diseases. Mutant variants of the virus are not recognized by the immune system and the treatment options are also limited. Additionally, antigenic shift and drift can lower the impact of vaccines.
The mutated virus after a shift is most likely to cause a pandemic since the population has no immunity towards it. This phenomenon was observed in the case of the severe acute respiratory syndrome coronavirus (SARS-CoV-1) and SARS-CoV-2. Although both of these viruses use the same angiotensin-converting enzyme 2 (ACE2) receptor for entry into host cells, the entry is more efficient in the case of SARS-CoV-2.
A similar phenomenon is observed in the case of the mutated Delta variant of SARS-CoV-2. The Delta variant can spread three times faster than the original strain and can also suppress the host immune system.
Although current COVID-19 vaccines are effective against the Delta variant, there remains the possibility that newer vaccine-resistant strains will emerge. Therefore, non-vaccine strategies must be implemented to prevent the spread of the disease.
Mechanism of antibiotic resistance
The rise in antibiotic resistance can lead to a future pandemic, while many scientists believe that we are already amid this “silent pandemic.” Antibiotic resistance can cause several everyday procedures to be unsafe.
Bacteria, despite being unicellular organisms, have survived for over three billion years due to their adaptability and genetic plasticity. These mechanisms also help the bacteria to acquire resistance to antibiotics, detergents, and disinfectants.
Gram-negative bacteria are more resistant to disinfectants due to their outer membrane. Therefore, these bacteria can persist in the hospital environment and cause disease to patients. Further research is needed to determine better control strategies that can prevent multidrug-resistant organism (MDRO) infections.
Disease transmission in healthcare facilities
Understanding the routes for disease transmission can be important in preventing disease transmission and future infections. The three factors for pathogen transfer include a susceptible host, a virulent pathogen, and a favorable environment.
Host factors are the most difficult to regulate, as many patients with comorbidities are admitted to hospitals. Vaccination is considered most relevant in the case of COVID-19; however, hospitals cannot discriminate against unvaccinated patients. Also, many infectious pathogens do not have available vaccines. Thus, the most relevant factor for the control of infection is the environment and pathogen.
The four main routes of disease transmission include vector, vehicle, contact, and airborne transmission. Contact transmission involves physical contact and direct transmission of pathogens between individuals.
Vehicle transmission is the indirect transfer of an infectious agent from a reservoir to the host. The most common vehicles in a hospital setting can be contaminated catheters, surgical instruments, or objects in patients' rooms.
Airborne transmission occurs when pathogens are suspended in the air and cause disease by entering the respiratory system. Finally, vector transmission is the spread of disease by animals.
Although there are many routes for hospital transmission, the emergence of COVID-19 has highlighted the importance of environmental disinfection. The use of personal protective equipment (PPE) is considered to be most important method of preventing viral transmission, followed by hand washing and maintenance of social distancing. These techniques are not effective alone; therefore, several vaccines have been developed to reduce the transmission of COVID-19.
The current approach to infection control
The first approach for preventing pathogen transmission is the maintenance of hand hygiene. Hand hygiene practices have led to a reduction in infections caused by MDRO.
However, hand hygiene alone is not sufficient, as the transmission of pathogens by vehicles often requires environmental cleaning. A detergent solution is used to clean clinical surfaces, while a disinfectant is used to clean higher-risk surfaces.
Furthermore, airborne transmission can be limited by utilizing an air filter. This includes face coverings, high-efficiency particulate absorbing (HEPA) air filtration, and ventilation procedures.
Wearing face masks has been common both among healthcare workers and common people during the COVID-19 pandemic. However, there is still a need for additional disinfection strategies to further reduce the transmission of pathogens like SARS-CoV-2. During the COVID-19 pandemic, UVC disinfection of air and surfaces has gained popularity throughout the world.
UV germicidal irradiation
Ultraviolet germicidal irradiation uses UV rays that are within the wavelength range of 200 to 320 nanometers (nm). UVA lies outside this range and is not considered germicidal. The most prominent germicidal UV is UVC, which is used in many commercial systems.
History of UV disinfection
The first report of the germicidal property of light was published in 1877 by Downes and Blunt. Following this, Marshal Ward showed that the violet end of the light spectrum could cause the inactivation of bacteria in 1892.
In 1903, Niels Finsen received the Nobel Prize in Physiology or Medicine for the treatment of tuberculosis-related diseases with concentrated light radiation. The bactericidal spectrum was developed by Gates in 1930. However, during this time, penicillin was also discovered, which shifted the focus from UV light.
In 1988, Bolton showed that UV light could act as a broad-spectrum disinfectant that was capable of inactivating almost all bacteria, viruses, and protozoa. Today, UV is widely used as a disinfectant because it is a chemical-free process and is quite effective against chemical-resistant organisms.
Mechanism of UV microbial inactivation
UV light causes microbial inactivation following its absorption by pathogenic genetic material. UV light is strongly absorbed by thymine-cysteine double bonds in pyrimidine bases, which causes the breaking of hydrogen bonds that further allows the pyrimidine base to react with neighboring molecules. UV can also result in cross-linking of non-adjacent thymines, or between cytosine and guanine.
UV targets deoxyribonucleic acid (DNA) rapidly. In fact, UVB causes between 50–100 double-stranded breaks in each cell, while UVC causes 50,000 pyrimidine dimers per cell.
However, these lesions can be repaired by the DNA repair mechanisms of the cell. UV light may also cause damage to the protein caps of certain viruses, alter protein secondary structures, cause protein unfolding or aggregation, and expose hydrophobic regions.
Clinical applications of UV disinfection
Although detergents are commonly used to clean surfaces, they do not inactivate antibiotic-resistant genetic material. These genetic materials subsequently persist in the environment and can get transferred to neighboring bacteria through horizontal gene transfer. Notably, detergents and disinfectants also have no impact on airborne pathogens.
However, the use of UV disinfection in hospitals is not very common yet, as it is not suitable for certain healthcare environments like emergency rooms. The most suitable use of UVC in hospitals is cleaning high-risk areas.
Upper room UV systems can be used in occupied rooms if they are suitably designed to limit UV exposure to the lower room. Enclosed UVC air filters and automated UV disinfection robots can be used anywhere in the hospital. UV disinfection is an additional cleaning strategy that must be used along with manual cleaning; however, it must not be as a replacement to manual cleaning.
When choosing a UV surface disinfection system in a hospital, certain criteria such as cost-effectiveness, easy usage, and transport must be met. Additionally, these UV devices must be fitted with multiple safety features, coupled with the implementation of certain safety measures that prevent leakage of light into the surroundings. Furthermore, the UV device must be cleaned and monitored regularly.
UVC activity against clinical pathogens
Several studies have reported that UVC is capable of inactivating high viral loads of both SARS-CoV-1 and SARS-CoV-2. Therefore, UVC is quite effective in reducing the transmission of SARS-CoV-2. UVC has also been found to inactivate MDROs and other antibiotic-resistant bacteria.
Airborne transmission of the pathogen
The accurate identification of SARS-CoV-2 transmission routes can provide implications for its spread in hospitals and communities. Several studies provide clear evidence that the transmission of SARS-CoV-2 occurs through the air. SARS-CoV-2 could also be transmitted by fecal aerosols through dried-out baths and floor drains.
UV disinfection of air
Disinfection of air and surfaces can be carried out with the help of UV robots; however, due to their mutagenic effects, they cannot be used in occupied rooms.
HEPA filtration is generally used to trap and limit the recirculation of particles in the air. However, the efficacy of HEPA filters is limited, as they cannot trap particles smaller than 0.3 micrometers (µm), which includes viruses, volatile organic compounds (carcinogenic), and some proteins. The diameter of SARS-CoV-2 has been estimated to be within the range of 60 to 140 nm, which is quite below the HEPA filter trap.
The latest air filtration systems use a hybrid of physical and biological systems. New technologies use HEPA filters along with UVC to disinfect particles. This improves the disinfection process and prevents the transmission of pathogens.
Upper UV room systems
Upper room UV systems create a germicidal zone of UVC light located at the uppermost portion of the room. The working mechanism behind upper UV room systems is to maximize UVC exposure of upper-room air while minimizing exposure for room occupants below. These upper room UV systems are useful for high-risk environments such as operating theatres or waiting rooms.
Some of the considerations for upper room UV systems include air exchange rates, UVC dose, UVC exposure time, ceiling height, humidity, temperature, exposure to medical equipment, and lamp maintenance.
Surface transmission of pathogens
Pathogens are shed daily from the skin of patients and healthcare workers, respiratory droplets, or aerosols that settle on surfaces and generate fomites. These pathogens are capable of surviving on surfaces for years.
Recently, SARS-CoV-2 was found to remain viable on non-porous surfaces for at least 28 days and 21 days on the N95 mask material. The pathogens often remain on these surfaces due to ineffective manual cleaning.
However, the risk of transmission of SARS-CoV-2 through exposure to contaminated surfaces is low as compared to direct and airborne transmissions. Nevertheless, it is important to understand the role of environmental surfaces in disease transmission.
Respiratory droplets and airborne particles of SARS-CoV-2 can settle on surfaces where they remain viable for seven days. Hand hygiene and surface disinfection are therefore extremely effective in preventing surface transmission.
UV disinfection of non-porous surfaces
Currently, several devices are available in the market that utilizes UV technology for use in healthcare facilities. To this end, two notable devices include pulsed xenon UV and steady-state UVC emitting devices. These technologies can effectively reduce the transmission of HAIs including MDROs, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant enterococcus (VRE).
UV disinfection of porous materials
One major consequence of the COVID-19 pandemic was the global shortage of PPE. Single-use PPE such as surgical masks, N95 respirators, and disposable gowns was reused for days at a time, which left healthcare workers at a high risk of infection.
During this time, UVC disinfection of single-use PPE was implemented to overcome the shortage. Many studies have shown that UVC irradiation was able to inactivate SARS-CoV-2 virions that were trapped in porous materials, especially face coverings. The use of UVC to decontaminate PPE not only reduced the risk of infection but also decreased costs and the volume of medical waste.
Studies also suggested that UVC was capable of reducing the microbial load of soiled masks while maintaining the mask material integrity. The UVC disinfection of these materials has certain criteria such as UVC must be in direct contact with the material and the target material must not be covered by other materials.
Conclusion
The current review explores the transmission of diseases in healthcare facilities and indicates that environmental disinfection is a key factor in preventing disease transmission. UV disinfection is highly effective; however, it does not replace manual cleaning of surfaces and should instead complement these procedures.
Concerning the current pandemic, UVC has been found to be quite effective in reducing the transmission of SARS-CoV-2. However, further research is still needed to determine the long-term benefits of UV disinfection, as well as the reduction of HAI rates using this technology for its regular use in clinical settings.
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