INFECTION CONTROL


Understanding the risks of pathogen aspiration


Elaine Waggott, director of Operations for recently established water hygiene/safety product manufacturers, Angel Guard and Water Kinetics (HEJ – February 2020), and a former head of the Business Development team within Scotland for Ideal Standard/Armitage Shanks, discusses some of the key risks posed by aerosol transmission of harmful pathogens, and in particular their part in healthcare-acquired infections.


The need to reduce the risks of splashing and airborne pathogenic aerosol has never been more important. In the wake of COVID-19, recent research findings have started to confirm what many already suspected – that COVID-19 acts like many existing pathogens in the ways it can be transmitted via waterborne particles and poor hand hygiene. Unacceptable levels of sickness and deaths have long been associated with poor hand hygiene, close contact with infected people, and inadequate cleaning. In many countries, initiatives addressing education, and cleaning and audit, together with compulsory reporting of infections, have brought about benefits, leading (in some cases) to a reduction in headline rates of infections such as methicillin- resistant Staphylococcus aureus (MRSA), Clostridium difficile (C. difficile) and Legionnaires’ Disease. It is readily accepted now that a common mode of transmission is contact between the patient, the staff, and the environment. Inappropriate hand hygiene practice has been identified as a significant contributor to numerous outbreaks. Several studies have shown the impact of improved hand hygiene on the risk of healthcare- associated infection and multi-resistant pathogen cross-transmission. To date, most studies have focused on MRSA.


Two groups of skin bacteria Bacteria present on human skin can be considered as belonging to one of two groups: resident and transient flora. Transient flora colonises the superficial layers of the skin. It has a short-term persistence on skin, but a high pathogenic potential. It is usually acquired by healthcare workers during direct contact with patients or contaminated environmental surfaces adjacent to the patient, and is responsible for most healthcare-associated infections, and for the spread of antimicrobial resistance resulting from cross-transmission. Resident flora is attached to deeper skin layers, and has a low pathogenic potential unless introduced into the body by invasive


Aerosol dispersal caused by a hand dryer.


devices. It is also more difficult to remove mechanically. Hand hygiene decreases colonisation with transient flora, and can be achieved either through handwashing or hand antisepsis.1


While studies have shown


that outbreaks can be reduced via improved hand hygiene compliance and better cleaning of the environment, airborne infection transmission has often been less well investigated, sometimes leading to complacency about this mode of transmission.


It has been proven already that Norovirus can be transmitted by aerosol, and is difficult to contain in a hospital ward without sufficient single rooms with en-suite toilets. Now, with the additional battle against COVID-19, transmission by aerosol needs to be urgently considered, and the risks substantially reduced.


Aerosol-generating procedures Although direct transmission from infected people is the primary source of aerosols and droplets, other scenarios, such as medical procedures, surgeries,2 and fast-running tap water and toilet flushes,3


also generate aerosols


contaminated with infectious pathogens. The most common types of virus causing infections in the respiratory tract through aerosol transmission are influenza viruses,


rhinoviruses, coronaviruses, respiratory syncytial viruses (RSVs), and parainfluenza viruses. Studies3,4


has postulated three


modes in which the influenza virus can be transmitted: aerosol transmission, droplet transmission, and self-inoculation of the nasal mucosa by contaminated hands.2 Historically, natural ventilation was seen to be beneficial in hospital wards, and was part of hospital design. With the advent of sealed high-rise buildings and forced ventilation, expensive negative pressure rooms have sometimes been introduced to house patients with infections thought likely to be transmitted by aerosol.


Bio-aerosol characteristics Aerosols can be defined as liquid or solid particles suspended in the air by humans, animals, instruments, or machines. Bio-aerosols are aerosols consisting of particles of any kind of organism.1,2 The characteristics of bio-aerosols differ depending on environmental influences such as humidity, air flow, and temperature. Aerosols, which are responsible for the transmission of airborne microorganisms by air, consist of small particles named droplet nuclei (1–5 μm) or droplets (>5 μm). Droplet nuclei can stay airborne for hours, transport over long distances, and contaminate surfaces by falling down.


September 2020 Health Estate Journal 23


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