Infection control: current status. risks, research, rules and recycling

Coronaviruses

The early years of the 21st century saw the emergence of the novel viral disease SARS (severe acute respiratory syndrome), an atypical pneumonia caused by a coronavirus named SARS-CoV-1.⁹ Management protocols were developed for the different clinical scenarios that dental practitioners may face if SARS were to re-emerge.¹⁰ The importance of universal precautions was stressed. It could be argued that the dental profession should have been better prepared for the risk of the COVID-19 pandemic, caused by another coronavirus, SARS-CoV-2. UK government planning documents have been criticized for over-dependence on influenza as a model for future healthcare emergencies.¹¹

Two main routes of transmission of SARS-CoV-2 include contact with contaminated objects and inhalation of droplets emitted by sneezes and coughs. Even stagnation of microdroplets generated during speech, particularly loud conversational breathing, has been suggested as a route for transmission.¹² Without mitigation strategies, the virus has high transmission potential, with an estimated basic reproduction number (the average number of secondary cases generated per case) of 2.6 in the UK prior to the first ‘lockdown’ on the 23rd March 2020.¹³

There have been monumental efforts across the world to contain and control the spread of SARS-CoV-2, including the development of new strategies for vaccination, therapy and diagnosis.¹⁴ ‘Lockdown’ and social distancing mitigation strategies have also had a devastating effect in themselves, leading to problems with mental and physical health and well-being, as well as yet unknown levels of disruption to dentistry, dental education and dental research.¹⁵

Influenza

Comparisons between the COVID-19 pandemic and the Spanish influenza pandemic of 1918 have been drawn.¹¹ The Spanish influenza pandemic devastated the world at the end of World War I, leading to the loss of between 50 and 100 million lives, as well as major effects on the politics and society of the time.¹¹

Influenza A viruses are responsible for most winter epidemics and affect animal species in addition to humans. When an influenza A virus subtype emerges, which is different from recent circulating strains, then an influenza pandemic can occur. In 2009, the H1N1 flu pandemic caused a fatality rate of 26 per 100,000 in England.¹⁶ This fatality rate was much lower than the flu epidemics of the 20th century. Older people were less susceptible than younger people, but more likely to die when affected.¹⁶ The Department of Health developed a UK influenza pandemic preparedness strategy in 2011,¹⁷ but as we have witnessed recently, the transmission of different pathogens varies greatly, and plans based on influenza are not necessarily applicable to other infectious agents. One positive effect of lockdown and social distancing COVID-19 mitigation strategies has been the reduction of seasonal influenza rates.¹⁸

Prion diseases

An epidemic of bovine spongiform encephalopathy occurred in cattle in the UK between 1985 and 1996. Subsequently variant Creutzfeldt–Jakob disease (CJD) was found in humans. Although such prion diseases are extremely rare, they pose challenges for dental settings. Prions are highly resistant to the usual decontamination procedures and as such it has been recommended that dental equipment used to treat a patient with known CJD should be destroyed after use.¹⁹

Ebola

Between 2014 and 2016, West Africa experienced an epidemic of Ebola viral disease (EVD), a lethal haemorrhagic fever. At the peak of the epidemic, infections were doubling every few weeks. Transmission of EVD is via direct contact with bodily fluids. Infections in healthcare settings occurred when infection control precautions were not strictly practised. The long incubation period of 21 days, and the fact that a proportion of infected individuals were asymptomatic or only mildly symptomatic, posed risks to workers in dental settings. It was suggested that if risk of EVD was possible, then elective dental treatment should be delayed for 21 days.²⁰

Zika

Zika virus is carried by the mosquito species, Aedes aegypti. It is thought to cause Guillain–Barré syndrome in adults and microcephaly in babies born to mothers who have acquired it. There is no effective vaccine or treatment.²¹ Normal precautions against blood-borne viruses are advised in dental practice.

Tuberculosis

Perhaps surprisingly, at the turn of the 21st century tuberculosis (TB) was regarded as an emerging infection in the UK. Reports from 2011 show that London had seen an increase of 50% in the number of cases of tuberculosis since 1999.²² More recently, there has been a welcome decline in TB rates in the UK; however, there are still significant inequalities regarding this disease. The most deprived 10% of the population experiences a rate of TB that is more than five times higher than the least deprived 10% of the population.²³ Multi-drug resistant TB also continues to pose a challenge.

The risk of transmission of TB in dental practice is thought to be similar to that of the general population.²⁴ Employing standard precautions, including high vacuum suction and providing good quality air ventilation, are of the utmost importance.

The current pandemic should provide an opportunity to learn how to respond to other health crises in the future. It was suggested in 2015, that dental ‘emerging infection’ leads should be appointed by public health organizations to provide early appropriate advice to dental professionals when new infections arise.²⁵ In the future, policymakers may still have to rely on emergency plans that are based on past events, but then be ready to modify these plans as soon as data emerge that differ from the accepted model. ‘Top-down’ responses may not be the most appropriate method to provide stability, and more open communication and understanding is required.²⁶

Infection control

Infection-control procedures are risk-management strategies. Infection control depends on putting effective barriers in place to prevent the transmission of infectious agents. The NHS provides standard infection prevention and control guidelines, covering hand hygiene, occupational exposure (needle-stick management), management of healthcare equipment, control of the environment, uniform policies and safe waste management. Prior to the coronavirus pandemic, adherence to guidelines regarding infection control in orthodontic departments was reassuringly high and most UK orthodontic departments had implemented policies that had been recommended by NICE and the British Dental Association. These practices ensured a high standard of cross-infection control in pre-pandemic times.²⁷ In 2020, Public Health England, alongside the NHS, provided guidelines regarding COVID-19 infection prevention and control,²⁸ including advice on personal protective equipment (PPE) and aerosol-generating procedures (AGPs), both of which are covered in more detail later. During 2020, the British Orthodontic Society published and updated advice regarding risk of aerosol generation during the range of orthodontic procedures,²⁹ although interpretation of this guidance is likely to be variable across practices and hospital settings. A review published in October 2020 found no definitive orthodontic clinical protocols supported by robust evidence, and suggested that resuming orthodontic treatment during the pandemic requires a particular focus on screening, minimizing aerosol generation, use of appropriate PPE, good ventilation and full adherence to decontamination principles.³⁰

Decontamination

In 2009, the Department of Health released decontamination technical memoranda, including the HTM 01-05 document. This document was updated in 2013 and outlines processes intended to raise the quality of decontamination work in primary care dental services (Figure 6).³¹

Immunization requirements

There have been staggering efforts to develop effective vaccines against SARS-CoV-2.³² In the UK, despite the largest-ever vaccination programme being rolled out in December 2020, it will take several months for the UK population to be vaccinated. In the week ending 7th March 2021, approximately 19 million individuals in the UK had been vaccinated.³³

All healthcare workers in the UK should have routine vaccinations against tetanus, diphtheria, polio, measles, mumps and rubella.⁸ Staff who have direct contact with bodily fluids should also be vaccinated against hepatitis B virus, TB and varicella zoster virus.⁸ The seasonal flu vaccine is advised for healthcare workers and successful campaigns have increased uptake for both healthcare workers and eligible members of the population. In the 2019 winter season, 75% of NHS staff were vaccinated against flu, the highest uptake ever.³³

Continuing professional development requirements

The General Dental Council recommends that dental professionals complete at least 5 hours of continuing professional development activity covering disinfection and decontamination in every CPD cycle.³⁴ In-practice training in infection control is important, particularly induction training for new members of staff.

While these rules represent current best practice, emerging evidence has challenged some of the assumptions used to formulate these rules.

PPE

In recent years, it was a common misconception that standard surgical masks provide protection against aerosols. Such facemasks used in dentistry, when worn correctly and changed frequently, offer only around an 80% filtration rate.³⁶ In fact, in 2008, the Health and Safety Executive recognized the challenges that would be associated with the supply of FFP3 respirators (which provide a 99% filtration rate) during any pandemic.³⁷ The early stages of the coronavirus pandemic were indeed associated with severe shortages of such PPE.³⁸

A Cochrane review of PPE for healthcare workers, updated in 2020, reported that the quality of the evidence regarding protection provided by increased PPE body coverage is low to very low, and that more extensive PPE leads to more difficulties putting the PPE on and off, reduced comfort and, therefore, potential for even more contamination.³⁹ Another important point is that much of the research is simulated, with none of the research included in the Cochrane review originating from dental settings.³⁵

Aerosol generation

Dental professionals may have had greater exposure to COVID-19 in the early stages of the pandemic than workers in other professions owing to the generation of aerosols encountered in so many aspects of dentistry. Dental nurses and dental practitioners were cited among the workers with the highest potential exposure to SARS-CoV-2 in May 2020.⁴⁰

The use of dental drills creates aerosol and splatter, commonly contaminated with blood, viruses, bacteria and fungi.⁴¹ An in situ study demonstrated that during orthodontic debond procedures involving use of a dental drill, a bioaerosol penetrated to the deepest level of the respiratory tree in an impactor model.⁴² Microbial aerosols generated in general dental practice settings have been found to dissipate after 30 minutes.⁴³ There has been very little evidence regarding transmission of viruses in aerosols, and this is particularly relevant because SARS-CoV-2 is present in saliva.⁴⁴ The Scottish Dental Clinical Effectiveness Programme (SDCEP) performed a rapid review of evidence related to generation and mitigation of aerosols in dentistry, and the associated risk of transmission of SARS-CoV-2.⁴⁵ The report categorized dental procedures according to aerosol production, recommended the use of high-volume suction and a pragmatic ‘fallow time’ after dental procedures producing aerosol particles less than 5 µm in size to reduce potential risk of SARS-CoV-2 transmission. A number of areas for further research and development were identified, as well as the need for standardized methodologies and outcome measures in the future. One study currently underway, AERosolization And Transmission Of SARS-CoV-2 in Healthcare settings (AERATOR), funded jointly by NIHR and UKRI, aims to characterize aerosols generated from patients across a range of healthcare settings, including dentistry, rather than simulated settings.

Glove use for non-surgical procedures

Glove use for non-surgical procedures in dental and orthodontic clinics is universal in the UK. However, there is no evidence that the wearing of gloves in non-surgical situations is more effective at preventing infection than scrupulous hand-washing. It has been proposed that clinicians who wear gloves in non-surgical situations may touch several potentially infected items, but simultaneously develop a sense of invincibility as a result of the gloves.⁴⁶ It is also thought that gloved clinicians may wash their hands less frequently owing to the difficulties of placing gloves on wet hands.⁴⁶ Others argue that wearing gloves reduces the risk of transmission of infectious agents found in saliva and transmission of blood-borne agents during needlestick injuries. The glove material reduces the volume of blood transferred.⁴⁷ In current dental practice, it is likely that serious medico-legal consequences, including action by the dental regulators, would result from not wearing gloves in either surgical or non-surgical scenarios.

Clinical attire

Regulations with regard to clinical attire have been adopted in recent years with the aim of reducing transmission of micro-organisms from healthcare workers to patients and vice versa. The Department of Health introduced the ‘Bare below the elbow’ policy in 2007, based on the idea of improving hand hygiene measures. However, this change in policy does not appear to be evidence based.⁴⁸ A study has shown that unsecured ties result in transmission of bacteria, but long sleeves are no more likely than short sleeves to transmit bacteria.⁴⁹ Interestingly, patients still prefer to see clinicians in suits and white coats. In particular, older patients feel that doctors should not wear scrubs, especially as it makes it difficult to distinguish doctors from nursing staff.⁵⁰

In orthodontics, wearing a white tunic was the preferred dress code, when compared to a range of options, for both female and male orthodontists.⁵¹ The public perception was that a white tunic demonstrated cleanliness and professionalism. Best practice at the time of writing is to change into and out of uniforms at work, and not to wear uniforms while travelling.⁵² Uniforms should be laundered separately, at temperatures of at least 60°C. It is likely that the frequency of uniform washing across the dental profession is below standard.⁵³ Changes to clinical attire and increased PPE as a result of the COVID-19 pandemic have caused problems with muffled speech and impaired non-verbal communication, especially for the elderly and the young.⁵⁴

Contamination of laboratory work

Intra-oral impressions are a common part of orthodontic practice for the construction of orthodontic appliances and study models. Poor disinfection practices potentially allow for the transmission of bacteria or viruses to surfaces and staff in the construction laboratories. Although relatively little is known about the transmission of bacteria or viruses from the laboratory back to the patient when fitting laboratory-constructed orthodontic appliances, a study by Barker et al.⁵⁵ based in a dental hospital, aimed to determine the bacterial load at each stage of the fabrication process in the dental laboratory. It also aimed to determine whether appliances were free from contamination prior to clinical use. Reassuringly, the results showed there was no evidence of contamination from patient saliva to the dental laboratory. However, the pumice solution in the laboratory that was used in conjunction with polishing wheels to polish removable appliances was found to contain bacteria of the Brevundimonas, Corynebacterium and Klebsiella genera (Figure 7). Of all the stages of laboratory appliance construction, the final removable appliance construction and polishing phase was found to be the most contaminated. A range of genera was identified on the appliances, some known to be capable of causing infections in susceptible or immunocompromised patients.⁵⁵ The two-way decontamination processes between clinics and laboratories may vary across different settings. More research is required to enable dental professionals, including laboratory staff, to eradicate the risk of cross-infection to patients and other team members.

Dental unit waterlines

Bacterial contamination of dental unit waterlines (DUWL) has been well researched and has demonstrated that some dental unit water is heavily contaminated with bacteria shed from biofilms adhering to the internal walls of the tubing in the dental unit. There have been incidents of both patients and dentists dying from Legionella spp infections where the evidence suggests that dental unit water supplies have been the source of infection. There is also speculation that exposure to the bacteria from contaminated waterlines has led to the development of late onset asthma in dentists.⁵⁶ It is, therefore, important that potential contamination of DUWL is well managed by a suitable chemical treatment, as part of an infection control risk-management strategy.

Recycling

The WHO reports that about 85% of the total waste generated by healthcare activities is categorized as general and non-hazardous. The remaining 15% can be considered hazardous material that is toxic, radioactive or infectious.⁵⁷ Hazardous waste is subject to additional controls, as specified in the Hazardous Waste (England and Wales) Regulations 2005.⁵⁸

The safe disposal of healthcare waste is a worldwide challenge. Its disposal may pose risks to health through the environmental release of pathogens and toxic pollutants. A joint WHO/UNICEF assessment found that only 58% of facilities from 24 countries have sufficient systems in place for the safe disposal of healthcare waste.⁵⁹

The WHO has also estimated that 89 million medical masks and 76 million medical examination gloves have been required each month in the response to the COVID-19 pandemic.⁶⁰ As these and many other disposable plastic products used in dentistry are classified as clinical waste, disposal is likely to involve incineration, with the resultant adverse effects on air pollution. The dental profession should have serious concerns about the environmental impact of these materials and the waste generated in both dental practices and hospital settings. High levels of electricity and water consumption are also important to consider.⁶¹

In 2013, the Department of Health released an updated version of HTM 01-05, where the rules regarding storage of dental instruments were reviewed (Figure 8). The emphasis is now on ‘ensuring effective decontamination and preventing contamination with another patient's blood and body fluid rather than on preventing environmental contamination of sterilized instruments’.³¹ There have also been changes to the type of dental instruments available in recent years. Decontamination and sterilization processes consume a large amount of energy and there has been a move towards single-use instruments, which eliminates the decontamination stages. However, this has added to the environmental impact of landfill and incineration. Recently there has been interest in the recycling of single-use surgical instruments.⁶²

Historically, cost implications are a major disincentive to creating an environmentally friendly workplace. Before the COVID-19 pandemic, attitudes were changing towards sustainable practice in dental care, and it had been argued that it was possible to reduce carbon emissions with potential cost savings.⁶³ The pandemic is likely to persist for some time and there will inevitably be delays in making sustainability a priority, especially as many dental practices are suffering financially. However, there is evidence from other natural disasters, such as the Christchurch earthquake in 2011, that pragmatic approaches that balance short-term needs against long-term goals, such as improved sustainability, are achievable.^64,65