AI R BORNE T RANSMI S S ION
size of £5µm and droplet aerosol size of >5µm. The terms aerosols and droplets are used but, in fact, they are both the same and are a result of particles expelled on exhalation suspended in the moisture from the breath of an individual. The size of the droplet is thought to determine how far the droplet will travel, with the larger droplets travelling the furthest before falling, compared to smaller droplets that start to evaporate quickly but can stay suspended within a cloud for a longer period.6
exhalation, the cloud of droplets will start to disperse with the available airflow until the droplets eventually fall.
Some have argued the distance that different droplet sizes travel is based on outdated evidence and fails to consider the physics of respiratory emissions.6
Droplets
exist in a variety of sizes and are held and moved with the hot turbulent gas cloud and moisture of the exhaled breath which enables the cloud to be carried over a distance in a few seconds. Singing, shouting, coughing and sneezing can move droplets further and potentially spread beyond 6-7 metres.
Several papers have evidenced the spread
of SARS-CoV-2 by airborne transmission. An interesting article describes an investigation, using whole-genome sequencing, of the transmission of SARS-CoV-2 on two wards leading back to the Emergency Department (ED). Although the ED had good ventilation and single rooms, patients still acquired COVID-19 infection in the ED, leading the authors to conclude that airborne transmission had occurred on more than one occasion.7
The relationship between hands and surfaces
Hand hygiene has always been promoted by infection preventionists as the single most important procedure to reduce the risk of infection and not many would argue against this. However, hands can become contaminated easily as the healthcare workers have continual contact with the environment such as door handles, privacy curtains,
Following
patients’ bed rails and patient equipment. Hands can even become contaminated after seemingly ‘clean’ procedures. Missed opportunities for hand hygiene contributes to the spread of microorganisms onto surfaces and the vicious cycle occurs with unclean hands contaminating surfaces and surfaces contaminating hands. A recent study at Great Ormond Street Hospital, using a non-pathogenic organism, showed how micro-organisms can transfer from an isolation room to almost half the frequent contact points outside the isolation room within 10 hours.8
The overuse and misuse
of gloves is common and results in missed opportunities for hand hygiene with gloves often put on too early and not removed promptly after a procedure is completed.
Failures of surface cleaning Micro-organisms have a great ability to survive for lengthy periods on hospital surfaces, for example, Clostridioides difficile can survive for many months on surfaces. As patient equipment becomes more complex and patient flow through the hospital increases, so does the challenge to keep surfaces clean. It is suggested that up to 50% of surfaces are missed in manual cleaning following terminal cleaning, increasing the risk of infection to the next occupant. We have known about wet biofilms creating a challenge to cleaning and disinfection for many years; these wet biofilms are associated with equipment where moisture is present. Perhaps more worrying is the little understanding and attention paid to the dry biofilms. Dry biofilms have been shown to be present on many hospital surfaces, despite cleaning, and harbour mainly gram-positive bacteria such as staphylococcus but also Acinetobacter species.9 Although dry biofilms are harbouring pathogens, further research is needed to understand their role in transmission. Moreover, poor cleaning and disinfection
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may further exacerbate the harbouring of pathogens.
What is the role of indoor air quality? During the SARS-CoV-2 pandemic we have learnt about the importance of indoor air quality (IAQ) in the hospital environment. Bed spacing, patient isolation and cough etiquette can only minimise airborne spread of micro-organisms. Many hospital wards have poor ventilation requiring additional technology to improve the IAQ.
Florence Nightingale, in her 1859 book,
‘Notes on Hospitals’, described her vision for a hospital ward as: “a large pavilion with soaring ceilings and plentiful windows, where patients would be separated, and clean air would circulate”. She advised hospital architects to avoid “closed corners, lest infectious air to stagnate”. The last 20 years has seen a shift from the old-fashioned Nightingale wards to small bays of 4-6 beds and single rooms, predominantly to provide privacy for patients and reduce the spread of infection. The refurbishment of these old wards has affected the airflow of fresh air through the ward areas creating poorer air quality. Even many of the newly built hospitals have been poorly designed in terms of providing adequately ventilated wards with some hospital rooms and staff rest rooms with no access to an external wall with an opening window.
Hierarchy of controls
During the pandemic there was an emphasis on the hierarchy of controls, particularly when it was realised that much weight had been placed on PPE, which in fact is suggested to have the lowest effect at controlling infection. The hierarchy of controls is a way of determining which actions will best control exposures, in this case, control the risk of infection. The hierarchy of controls has five levels of actions to reduce or remove the hazard, with the preferred order of action based on
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